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PLATINUM METALS REVIEW A Quarterly Survey of Research on the Platinum Metals and of Developments in their Application in Industry www.platinummetalsreview.com

VOL. 50 OCTOBER 2006 NO. 4

Contents High-Temperature Mechanical Properties of the Platinum Group Metals

158

By R. Weiland, D. F. Lupton, B. Fischer, J. Merker, C. Scheckenbach and J. Witte

Rhodium and Iridium in Organometallic Catalysis

171

By Robert H. Crabtree

CAPoC7: The State of the Art in Automotive Pollution Control

177

Reviewed by Jillian Bailie, Peter Hinde and Valérie Houel

The Platinised Platinum Interface Under Cathodic Polarisation

180

By Jacques Simonet

SURCAT 2006 Conference

194

Reviewed by S. E. Golunski

Reliability of Platinum-Based Thermocouples

197

By Roy Rushforth

“Principles of Fuel Cells”

200

Reviewed by Tom R. Ralph

10th Ulm Electrochemical Talks

202

Reviewed by Sarah C. Ball

Susan V. Ashton

205

By M. C. F. Steel

Abstracts

207

New Patents

211

Indexes to Volume 50

213

Communications should be addressed to: The Editor, Barry W. Copping, Platinum Metals Review, [email protected]; Johnson Matthey Public Limited Company, Orchard Road, Royston, Hertfordshire SG8 5HE

DOI: 10.1595/147106706X154198

High-Temperature Mechanical Properties of the Platinum Group Metals PROPERTIES OF PURE IRIDIUM AT HIGH TEMPERATURE By R. Weiland and D. F. Lupton* Engineered Materials Division, W. C. Heraeus GmbH, Hanau, Germany; *E-mail: [email protected]

B. Fischer, J. Merker and C. Scheckenbach Department SciTec, Precision-Optics-Materials-Environment, University of Applied Sciences Jena, Germany

and J. Witte Melting Technology, SCHOTT Glas, Mainz, Germany

In order to provide reliable data on the high-temperature deformation behaviour of iridium, the high-temperature material properties such as stress-rupture strength, high-temperature tensile strength and creep behaviour are determined for pure iridium in the temperature range 1650–2300ºC. Analyses of the stress-rupture curves and the creep behaviour of pure iridium samples at 1650ºC, 1800ºC and 2000ºC imply that the fracture behaviour is controlled by two different fracture mechanisms depending on test conditions, in particular applied load and test temperature. The existence of the different fracture modes is confirmed by SEM examination of the fracture surface of samples ruptured at high temperatures. Anomalies in the creep curves and the results of high-temperature tensile tests indicate that dynamic recrystallisation plays an important role in the high-temperature deformation behaviour of pure iridium.

Due to their excellent chemical stability, oxidation resistance, and resistance to the action of many molten oxides, the platinum group metals (pgms): iridium, platinum and rhodium are widely used for high-temperature applications involving simultaneous chemical attack and mechanical loading (1). Although iridium is more sensitive to oxidation than platinum or rhodium, it is the most chemically resistant of all metals. Its resistance to attack by stable oxide melts is maintained up to temperatures above 2000ºC. The melting point of iridium (2454ºC) (2) and its high strength even at temperatures above 2000ºC make it a particularly suitable material for applications under extreme thermal and mechanical conditions which preclude the use of platinum alloys or rhodium. Important applications of iridium and iridium alloys are as crucibles for pulling single crystals (e.g. yttrium-aluminium garnet (YAG)) and components for manufacturing and processing high-melting special glasses.

Platinum Metals Rev., 2006, 50, (4), 158–170

A knowledge of the high-temperature properties of a material, for instance stress-rupture strength and creep behaviour, is crucially important for the design of components used at high temperatures. The current investigation is part of an extensive test programme focused on the determination of the high-temperature mechanical properties of the pgms, such as the stress-rupture strength, creep behaviour (3) and elastic properties (4). In this work new investigations into the hightemperature properties of iridium are presented for the temperature range between 1650ºC and 2300ºC. The results are discussed in conjunction with data determined from earlier studies (3).

Methodology for Stress-Rupture and High-Temperature Tensile Tests The stress-rupture strength and the creep behaviour of pure iridium and iridium alloys were determined with a testing facility developed at the University of Applied Sciences Jena. The testing

158

Fig. 1 Schematic diagram of equipment for high-temperature creep measurements

device, for the measurement of high-temperature material properties up to 3000ºC, is shown schematically in Figure 1. It consists of a gas-tight specimen chamber which permits investigations either in air or under a protective gas atmosphere. In the case of iridium and iridium alloys, a gas mixture of argon with 5 vol.% H2 was used to protect the material from oxidation and thus avoid a reduction in cross-section of the sample due to evaporation of volatile oxides (5, 6). The load can be applied in two different ways. For the constant-load stress-rupture experiments the load is applied via a steel pull-rod by means of calibrated weights. For the high-temperature tensile tests the specimen chamber is mounted in a commercial servomotor-driven test machine and the steel pull-rod is connected to the load cell at the crosshead of the test machine. This allows a controlled variation of the applied load. Non-standard specimens (with typical dimensions of 120 mm × 4 mm × 1 mm) were used for all measurements. The samples were laser cut from hot rolled sheet material. The sample orientation was chosen parallel to the rolling direction. Direct electrical heating achieves high heating and cooling rates for the samples. The ohmic heating method allows easy access to the sample, and generally straightforward operation. The temperature is measured by a non-contact-

Platinum Metals Rev., 2006, 50, (4)

ing technique using a digital pyrometer (INFRATHERM IS10). The infrared pyrometer has a small measurement spot (approximately 0.5 mm in diameter). Due to the ohmic heating the highest temperatures are found in the central part of the sample. This region is therefore scanned continuously by the pyrometer via a tilting mirror. By storing the maximum value of emitted radiation, the maximum temperature at the surface of the sample may be determined. This value is used to adjust the heating current via a thyristor regulator connected to the primary winding of a 100 kVA transformer. The sample, short-circuited across the secondary winding of the transformer, is heated by alternating current at 50 Hz. Over a zone 30 mm in length around the centre of the sample the temperature usually does not vary by more than ± 5ºC. Once “necking” occurs in the sample, the temperature outside the necking region decreases, whereas the temperature within the necking region remains constant at the intended value. The design of the equipment thus guarantees uniformity of temperature throughout the duration of the test, despite the sample deformation. The strain is measured with a non-contacting video extensometer consisting of a 17 mm charge coupled device (CCD) camera with 1280 × 1024 pixel resolution. A special arrangement of telecentric lenses allows only near-parallel rays to pass the

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aperture, thus minimising perspective distortions caused by variations in the distance to the object. Both the CCD camera and frame grabber are controlled by “SuperCreep” software, developed at the University of Applied Sciences Jena, which uses digital image analysis. As mentioned above, ohmic heating causes the highest temperature to be limited to the central part of the sample, to which creep deformation is normally also limited. Strain at this part of the sample is determined by “SuperCreep” from continuous measurements of the distance between two markers. Suitable markers for high-temperature tests on sheet materials are made by laser machining samples of the material with four small shoulders (Figure 2). The distance between the two corresponding markers on the same side of the sample is 10 mm. Since the part of the sample between the markers experiences a uniform temperature, the exactness of strain measurements can be guaranteed, without their being influenced by the temperature gradients near the ends of the sample. A detailed description of the testing facility and the algorithm for strain measurement is given in (7) and (8).

Material Preparation The iridium raw material was melted inductively at 2550ºC in air in a zirconia crucible. After elemental analysis the ingot was forged at temperatures between 1400ºC and 1600ºC. The forged

material was then hot rolled at moderate temperature to 1 mm thick sheet. The iridium sheet was finally subjected to a special annealing procedure so as to recrystallise the deformed material without significant grain growth.

Scanning Secondary Ion Mass Spectrometry (Scanning SIMS) The microanalytical investigations were performed with a Cameca IMS 4f-E6 scanning secondary ion mass spectrometer. Secondary ion mass spectrometry (SIMS) allows the detection of very small amounts of impurity elements in the matrix. Since both the species of detectable secondary ions and their detection limits differ as between the positive and negative secondary ion spectra, different primary ions were chosen for the excitation of the secondary ions. Oxygen primary ions were used for the investigation of the positive secondary ion spectrum emitted by the iridium samples. The emission of the negative spectrum was induced by caesium primary ions. It could thus be ensured that all possible impurity elements contained in the iridium samples were detected. Metallographically prepared samples were used for the scanning SIMS investigations. So as to be able to investigate impurity levels both inside the grains and at the grain boundaries, areas of the samples containing grain boundaries were chosen. It should be mentioned that the intensity of the emitted secondary ion spectrum is dependent on the crystallographic orientation of the grains. Thus, if several grains with different orientations are contained in the area under investigation, this will be indicated by differences in the brightness attributable to the respective grains due to differences in ionic emissivity. Thus grain boundaries may be identified in the secondary ion spectrum, even if they do not contain significant amounts of impurities.

Stress-Rupture Strength Results

Fig. 2 Image of a creep sample with markers for the video extensometer (7)


The stress-rupture strength of pure iridium was determined in the temperature range 1650–2300ºC. The results of these investigations are summarised in Figure 3. The present experiments showed an excellent degree of

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Fig. 3 Stressrupture strength of pure iridium in the temperature range between 1650ºC and 2300ºC

reproducibility; the results are in good agreement with those of corresponding measurements for shorter testing times reported earlier (3). In contrast to the conclusion in (3), additional data on stress-rupture strength obtained recently, together with a detailed analysis of the rupture behaviour (see below under ‘Fracture Behaviour Results’), led to the conclusion that the stress-rupture data can best be approximated by two intersecting lines. The discontinuity in the slope of the stress-rupture curves correlates very well with a change in the fracture behaviour of the samples examined. Under high loads pure iridium shows a ductile fracture mode, whereas under low loads and long times to rupture, iridium tends towards brittle intercrystalline fracture. In fact, the discontinuity does not usually occur as sharply as indicated in Figure 3. Samples taken from near the discontinuity often show mixed fracture modes, partly intercrystalline and partly transcrystalline. Since insufficient stress-rupture data in the range of the transition are available, the stress-rupture curves for the temperatures between 1650ºC and 2000ºC are approximated for the sake of simplicity in the manner shown in Figure 3. In particular, the stress-rupture curve at 2000ºC shows a very pronounced change in the slope at loads between 4 and 5 MPa. This leads to strongly reduced stress-


rupture strength values at testing times longer than 300 h. It is not yet clear whether this steep decrease in slope can be attributed solely to the change in fracture mechanism, or whether the effect of weakening of the grain boundary coherence is enhanced by very small amounts of impurities accumulating at the grain boundaries after long testing times at high temperatures. As reported below, secondary ion mass spectrometric investigations showed that the impurity content in the iridium samples examined is very low. Nevertheless, it cannot be excluded that even very small amounts of impurity elements accumulating at the grain boundaries can have a detrimental effect on grain boundary coherence, thus leading to significantly reduced times to rupture. Measurements at 1650ºC and 1800ºC have been performed up to approximately 1000 h duration. Extrapolations to testing times longer than 10,000 h may not be considered meaningful. Data on the stress-rupture behaviour of pure iridium at 2200ºC and 2300ºC are available up to times to rupture of approximately 500 h and 150 h, respectively, and not as yet for longer times to rupture. Within the available range the stress rupture curves do not show a visible discontinuity in slope. Because of the very distinct decrease in slope in the stress-rupture curve at 2000ºC under low loads, no extrapolations beyond the measured times to rup-

161

Table I

Stress-Rupture Strength of Pure Iridium at Various Temperatures Time to rupture, h

1 10 100 1000 10,000

Stress-rupture strength, MPa 1650ºC

1800ºC

2000ºC

2200ºC

2300ºC

31.8 27.7 15.6 8.8 5.0

24.4 18.4 11.0 7.0 4.4

14.1 8.9 4.6 1.5 –

7.1 4.4 2.7 – –

5.4 3.3 2.0 – –

ture have been performed for the data at 2200ºC and 2300ºC. The interpolated and extrapolated data on the stress-rupture strength of pure iridium at different temperatures are given in Table I.

Creep Behaviour Results The investigation of the high-temperature deformation behaviour of iridium revealed that, depending on test temperature and load, its creep behaviour can be described by two types of creep curve which differ significantly in shape.

Fig. 4 Creep curves: (a) of pure iridium at 1650ºC under a constant load of 13 MPa in Ar/H2 atmosphere, and (b) corresponding creep rate as a function of time. The mean creep rate for the period 16.95–152.54 h is 1.3 × 10–7 s–1


Particularly at the lowest test temperature of 1650ºC, under moderate load, the creep behaviour is represented by typical creep curves such as those in Figures 4(a) and 4(b). These figures represent the creep behaviour of pure iridium at 1650ºC under a constant load of 13 MPa exhibiting the three well known stages of creep – primary, secondary (or steady-state), and tertiary – frequently reported in the literature. Under higher load, and particularly at higher test temperatures, the creep curves of iridium show significant anomalies. In the range of steadystate creep the creep curve contains different plateaus, as shown in Figure 5. These plateaux are separated by an acceleration of the elongation. This acceleration of creep is clearly visible in Figures 5(b) and 5(d). The phenomenon may be caused by dynamic recrystallisation, as was reported in (9) and (10), whose authors obtained creep curves of similar shape when investigating the creep behaviour of lead and copper, respectively. It can be seen in Figures 5(c) and 5(d) that in some cases more than one discontinuity occurs in the secondary creep stage. This indicates that dynamic recrystallisation takes place successively several times during the secondary stage of creep. This is called periodic or cyclic creep (11). These accelerations of creep complicate the determination of a constant creep rate in the secondary creep range. The creep rate has therefore been calculated as an average for a time range from 10% to 90% of the period of measurement. Thus additional contributions to the average creep rate from the accelerated creep in the transient creep stages are included in the values. This aver-

162

Fig. 5 Elongation and creep rate of pure iridium as a function of time in Ar/H2 atmosphere at 1800ºC for loads of: (a) and (b) 13 MPa. The mean creep rate at a constant load of 13 MPa for the period 5.68–51.12 h is 1.0 × 10–6 s–1. (c) and (d) 9.5 MPa. The mean creep rate at a constant load of 9.5 MPa for the period 22.5–225 h is 2.6 × 10–7 s–1

age creep rate has been used instead of the minimum creep rate for the calculation of the Norton plot (Figure 6). In the Norton plot, the average creep rate for pure iridium determined in this way for each test temperature is shown as a function of the initial applied stress on a double logarithmic scale. For the calculation of approximate trend lines,

the stress dependence of the average creep rate has been assumed to obey a power law (Equation (i)): dε/dt = f (S, T) σ

n

(i)

where ε is the elongation and f (S, T) is a function of the structure of the material and of the temperature. For the isothermal representation in the Norton diagram, f(S, T) has been assumed con-

Fig. 6 Average stationary creep rate of pure iridium as a function of the applied initial stress for temperatures between 1650ºC and 2300ºC (Norton plots)


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Table II

Coefficients for the Approximation of the Quasi-Stationary Creep Rate as a Function of Stress According to Equation (i) Temperature, ºC

f(S,T)

f1(S,T)

f2(S,T) n

Norton exponents n1 n2

–

1.3 × 10–13

4.5 × 10–25

–

5.35

13.68

1800

–

–11

1.2 × 10

4.4 × 10–16

–

4.40

8.28

2000

–

5.1 × 10–10

3.6 × 10–11

–

4.11

5.70

2200

2.5 × 10–9

–

–

5.38

–

–

2300

2.1 × 10–8

–

–

4.99

–

–

1650

stant. The effects of structural changes, for instance, due to recrystallisation, have been addressed to some extent by the use of the average creep rate, determined as described above. The Norton exponent, n, contains information about the nature of the prevalent creep mechanism in the sample. For creep mechanisms that are based only on the diffusional transport of material due to vacancy gradients either inside the grains (12, 13) or along the grain boundaries, a nearly linear stress dependence of the creep rate will be obtained, and n will be close to or equal to unity. For creep processes that are determined mainly by diffusioncontrolled dislocation climb, n falls between 3 and 5 for many common pure metals. In rare cases, n values up to 11 have been found. The distinction between the different creep mechanisms under low and high loads mentioned in the preceding section must also be taken into account in the Norton plots. The data for each test temperature between 1650ºC and 2000ºC are therefore approximated by two intersecting straight lines. As already explained for the stressstrain diagram, the information available for 2200ºC and 2300ºC does not allow this distinction to be made for these temperatures. For test temperatures between 1650ºC and 2000ºC, the values obtained for the Norton exponent under low loads n1 fall in the range between 4 and 5.5, and are thus in good agreement with the above-mentioned values of the Norton exponent for diffusion-controlled dislocation climb in many other pure metals. For conditions under which iridium exhibited a ductile fracture mode, i.e. under high loads, the Norton exponent n2 took


considerably higher values (5.7 < n2 < 13.7), indicating that under these test conditions diffusion-controlled dislocation climb is not the prevalent mechanism of deformation. The values for f(S,T), n1 and n2 determined by approximation of the experimental data in the Norton plot using Equation (i) are listed in Table II. The temperature dependence of the stationary creep rate can be expressed by an Arrhenius term. Thus, Equation (i) can be rewritten in the form (Equation (ii)): dε/dt = α σ n exp–(QC/RT)

(ii)

where α is a factor dependent on structure, QC is the activation energy for creep, R is the gas constant and T is the temperature in K. The activation energy, QC, for the creep mechanism can be obtained by plotting ln(dε/dt) versus 1/RT. If QC is independent of temperature, ln(dε/dt) will show a linear dependence on 1/RT, with the slope of the straight line equal to the activation energy QC. In the present investigations it was not possible to determine QC in the way described, as the creep tests were performed under constant load, not under constant stress. In this case the true stress is a function of the elongation, thus invalidating this method for determining the activation energy.

Fracture Behaviour Results The iridium samples showed excellent ductility at the temperatures investigated. Particularly at high loads, rupture strain values up to 100% have been measured. At lower loads, the values for the rupture strain proved to be considerably smaller.

164

Fig. 7 SEM images of the surface area near the fracture for pure iridium after stress-rupture test at 1800ºC under an initial load of 6.7 MPa: (a) and (c) ×20; (b) ×100; (d) ×50

This finding is in accordance with the observation that iridium exhibits two different fracture modes in stress-rupture tests at high temperatures. According to the literature (9) this change in fracture mode should be accompanied by a discontinuity in the slope of the log-log plot in the stress-rupture diagram (Figure 3). Whereas intercrystalline fracture occurs without necking at low loads (Figures 7(a) and 7(b)), together with the appearance of extensive intercrystalline crack formation across large parts of the sample (Figures 7(c) and 7(d)), the fracture at high stresses occurs by the transcrystalline mode, accompanied by extensive necking as shown in Figures 8(a) to 8(c). This is in accordance with textbook reports (11) of creep crack behaviour at high temperatures for many materials which are prone to brittle intercrystalline fracture under low loads, but tend to transcrystalline fracture under high loads. It should be mentioned that the numerous cracks and fissures occurring along the grain boundaries during the creep tests under low loads


make an additional contribution to the elongation of the sample. This apparent ductility does not, however, influence the intrinsically brittle mode of fracture. Samples exposed to high stresses exhibited only very few intercrystalline cracks. As a consequence the high apparent ductility of those samples can be assumed to be identical to the true ductility of the material. On the surface of the samples exhibiting ductile fracture behaviour, slip bands that have formed in the necked region are clearly visible. These are very distinct, and in some cases extend across grain boundaries, sometimes covering several grains. Overlapping slip bands in different directions were observed in some grains. This indicates that different slip systems have been activated during the creep experiments. It is not yet clear whether the slip bands are formed only in the final stage of creep deformation, when the load-carrying crosssection of the sample is significantly reduced due to progressive strain and the true stress and creep rate increase rapidly, or whether the slip bands are

165

Fig. 8 SEM images of the surface area near the fracture for pure iridium after stress-rupture test at 1800ºC under an initial load of 18 MPa: (a) ×10; (b) ×50; (c) ×500; (d) ×200

formed throughout the creep experiment.

High-Temperature Tensile Tests These tests were carried out in order to examine the behaviour of pure iridium at high temperatures under dynamic loading. Figure 9

summarises the results for the temperature range between 1600ºC and 2300ºC. The shapes of the stress-strain curves, particularly those for temperatures between 1800ºC and 2100ºC, are typical for materials that undergo dynamic recrystallisation. After a very steep rise in the stress-strain curve at Fig. 9 Stress-strain diagram for pure iridium at different temperatures


166

the beginning of the tests, the slope of the curve decreases, probably due to both plastic deformation and softening of the material caused by dynamic recovery. When dynamic recrystallisation commences, the softening becomes more severe and the load decreases. This is followed by a period at a more or less constant load – in some cases this phase exhibits a slight oscillation – until the stress drops rapidly when the sample ruptures. This behaviour is typical for materials that are recrystallising dynamically during the high-temperature tensile tests. A comparison of the stress-strain curves with the results of the SEM investigations reported in the previous section shows that the slip bands, shown in Figures 8 and 10, are formed only in samples exposed to loads close to or greater than the yield stress determined in the tensile test at the corresponding temperature. In the present investigation, the deformation mechanism under high loads at high temperatures appears to be based on an interaction of plastic deformation due to dislocation slip with common creep deformation. The plastic deformation in turn leads to an increase in the internal deformation energy, thus promoting the initiation of dynamic recrystallisation. Yield strength, Rp0.2, tensile strength, Rm, and tensile elongation, A, as determined in the hightemperature tensile tests are plotted in Figure 11 as a function of temperature. Measurements were

Fig. 10 SEM image (×200) of the surface morphology of an iridium sample after creep test at 1800ºC under 23 MPa load

made on at least three samples for each test temperature. The values given for Rp0.2 and Rm are averages over all three measurements. The standard deviation is indicated as an error bar for each data point, revealing excellent reproducibility for the measurements. The values for A, however, showed a greater scatter. Moreover, some of the samples did not rupture between the markers, in which cases it was not possible to determine the tensile elongation with the “SuperCreep” software. No error bars are given for the relevant data points in Figure 11.

Metallographic Investigations The microstructure of pure iridium exposed to the influence of high temperatures and different

Fig. 11 Yield strength, Rp0.2, tensile strength, Rm, and tensile elongation, A, of pure iridium as a function of temperature


167

Fig. 12 Longitudinal section of pure iridium in the initial recrystallised state

Fig. 13 Longitudinal sections of pure iridium after creep test at 1800ºC, 6.7 MPa, 1403.7 h

loads during the creep tests was evaluated metallographically. Comparative investigations were carried out on longitudinal sections of samples before and after creep testing. The microstructure of a sample in the initial state (i.e. before creep testing) is shown in Figure 12. The sample exhibits a uniform microstructure with an average grain size of about 100 μm. Comparison with metallographic sections of samples that were exposed to high temperatures under different loads (Figures 13 and 14) shows that during creep tests specimens have undergone the expected severe grain coarsening. Due to the high temperatures and long test times, very coarse grains with grain sizes up to 4 mm have formed. Furthermore, the samples exhibit strong intercrystalline crack formation as mentioned above. Figures 13 and 14 show that several – partly very deep – cracks have formed within the same sample. Nevertheless, the material withstood this


damage and cracked at a different position, several hours later. Dynamic recrystallisation is apparent in areas of high stress concentration and strong deformation, for instance at crack tips (Figure 13(a)), and close to the fracture in the necking areas (Figure 15). Particularly in the area around the crack tips, this may have led to a reduction in local stresses. As a consequence the crack propagation may have stopped in this area and continued in another part of the sample. The metallographic images show the existence of individual voids along grain boundaries and their coalescence into large pores. These are typically found in materials that have undergone creep deformation. This phenomenon is most frequently observed on grain boundaries that are oriented perpendicular to the direction of applied stress. This often leads to the formation of intercrystalline creep cracks during the final period of creep deformation.

168

Fig. 14 Longitudinal sections of pure iridium after creep test at 1800ºC, 13 MPa, 56.8 h

Fig. 15 Longitudinal section through the fracture tip of pure iridium after creep test at 1800ºC, 8.3 MPa, 385.9 h

Microanalytical Investigations As has been demonstrated in previous investigations (14–19), iridium generally tends to brittle intercrystalline fracture due to trace impurities at grain boundaries. Investigation by SIMS on the present iridium samples has shown a very high purity for the material. Only very small traces of impurities in the ppm range were detected, showing no enrichment at the grain boundaries. All the elements detected were distributed homogeneously in the matrix.

Conclusions Due to its outstanding properties iridium is particularly suited to applications under extreme thermal, chemical and mechanical conditions. In order to obtain the materials data necessary for the design of high-temperature equipment and the


numerical simulation of its service performance, the stress-rupture strength, creep behaviour and tensile properties of iridium have been measured over the temperature range 1650–2300ºC. The investigations were performed on hot rolled iridium sheet. The results showed a very good degree of reproducibility. The iridium samples exhibit very high stress-rupture strength. A discontinuity in the slope of the stress-rupture curves indicates the existence of two different fracture modes, depending on the temperature and the initial load applied to the samples. The existence of different fracture mechanisms was confirmed by the examination of the fracture surfaces. The change in fracture mode is probably caused by different deformation mechanisms prevalent under the various test conditions. A significant anomaly was observed in the creep behaviour of pure iridium – the creep curves contained plateaus in the range of steady-state creep. Metallographic examination, investigations by SEM, and high-temperature tensile tests indicated that dynamic recrystallisation may be the cause of this phenomenon. A further influence may be the activation of various slip systems which can be deduced from the observed slip bands. Microanalytical investigations by means of scanning SIMS showed a very high purity of the iridium heats investigated, without any enrichment of trace impurities at the grain boundaries. Initial results on the stress-rupture strength of an iridium-rhenium alloy doped with hafnium and molybdenum indicate that this alloy exhibits rup-

169

ture times three to four times longer than for pure iridium. Moreover, this alloy shows outstanding ductility, comparable to that of pure iridium. This alloy is therefore of particular interest for hightemperature applications and is the subject of ongoing research.

7 8 9

Acknowledgements

10

The authors would like to thank Margit Friedrich (SEM investigations), Erik Hartmann and Frank Lehner (creep tests) from the Department SciTec of the University of Applied Sciences Jena for their support for these investigations.

11

References

14

1 “Edelmetall-Taschenbuch”, eds. G. Beck, H.-H. Beyer, W. Gerhartz, J. Hausselt and U. Zimmer, OMG AG & Co KG, Giesel Verlag GmbH, Isernhagen, 2001 2 C. R. Barber, Platinum Metals Rev., 1969, 13, (2), 65 3 B. Fischer, A. Behrends, D. Freund, D. F. Lupton and J. Merker, Platinum Metals Rev., 1999, 43, (1), 18 4 J. Merker, D. Lupton, M. Toepfer and H. Knake, Platinum Metals Rev., 2001, 45, (2), 74 5 D. F. Lupton and B. Fischer, Proceedings of the Second European Precious Metals Conference, Lisbon, 10th–12th May, 1995, Eurometeaux, Brussels 6 J. Merker, B. Fischer, D. F. Lupton, C. Scheckenbach, R. Weiland and J. Witte, Proceedings of Processing and Fabrication of Advanced

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Materials XIII, Singapore, 6th–8th December, 2004, Stallion Press, Singapore, 2005, pp. 787–799 R. Voelkl, D. Freund and B. Fischer, J. Test. Eval., 2003, 31, (1), 35 R. Voelkl and B. Fischer, Exp. Mech., 2004, 44, (2), 121 J. N. Greenwood and H. K. Worner, J. Inst. Met., 1939, 64, 135 M. J. Luton and C. M. Sellars, Acta Metall., 1969, 17, (8), 1033 R. E. Reed-Hill and R. Abbaschian, “Physical Metallurgy Principles”, 3rd Edn., PWS Publishing Company, Boston, 1994 C. Herring, J. Appl. Phys., 1950, 21, (5), 437 F. R. N. Nabarro, Proceedings of the Bristol Conference on Strength of Solids, Physical Society of London, 1948, p. 75 P. Panfilov, A. Yermakov, V. Dmitriev and N. Timofeev, Platinum Metals Rev., 1991, 35, (4), 196 P. Panfilov and A. Yermakov, Platinum Metals Rev., 2001, 45, (4), 179 J. Merker, M. Schlaubitz, H.-J. Ullrich, S. Garbe, A. Knoechel, M. Radtke, F. Lechtenberg, D. F. Lupton and B. Fischer, DESY-HASYLAB Annual Report, Hamburg, Germany, 1994, pp. 913–914 J. Merker, D. F. Lupton, B. Fischer, M. Schlaubitz, H.-J. Ulrich, A. Gebhardt and S. Garbe, Prakt. Metallogr., Sonderband 27, 1995, pp. 267–270 J. Merker, D. F. Lupton, H.-J. Ullrich, M. Schlaubitz and B. Fischer, Proceedings of the TMS Annual Meeting, 2000, TMS, Warrendale, Pennsylvania, pp. 109–120 R. Voelkl, A. Behrends, J. Merker, D. F. Lupton and B. Fischer, Mater. Sci. Eng. A, 2004, 368, (1–2), 109

The Authors After studying Materials Science at the University of Saarbrücken, Germany, Reinhold Weiland worked as a research associate at the Max-Planck-Institute for Metals Research in Stuttgart, and received his doctoral degree from the University of Stuttgart. Since 2002 he has been working at W.C. Heraeus GmbH in Hanau as a development project manager. His main interests are the processing and manufacture of precious metals products and composite materials. Carolin Scheckenbach studied materials technology at the University of Applied Sciences in Jena, Germany, where she received her diploma degree. After one year as a research associate, she is now working as a trainee in the Department of Melting Technology and Hot Forming at Schott AG, Mainz.


Jürgen Merker studied materials science at the Technical University, Dresden, where he also earned his Ph.D. degree. Between 1995 and 2000, he worked as a development project manager for W. C. Heraeus GmbH, Hanau. After a short time in the R&D department of KM Europa Metal AG, Osnabrück, he was appointed to a Professorship in Materials Engineering and Applied Metals Science at the University of Applied Sciences Giessen-Friedberg in 2002. In 2006 Dr Merker became Professor of Materials Technology and Materials Testing at the University of Applied Sciences Jena. Prof. Dr David Lupton is Development Manager, Engineered Materials Division, W. C. Heraeus. His main interests are the manufacture and applications of precious metal and refractory metal products.

Prof. Dr.-Ing. habil. Bernd Fischer studied mechanical engineering and materials science at the Technical University Chemnitz, Germany. After more than 25 years at the University of Jena, Bernd Fischer was appointed to the Chair of Materials Science at the University of Applied Sciences Jena in 1992. For many years, his research interests have included the properties and applications of noble and refractory metals. Jörg Witte studied chemistry at the Technical University of Darmstadt, Germany, from which he received his doctoral degree in Materials Science. Since 1999 he has worked at Schott-AG, Mainz, where he is currently head of the Materials Competence Department. His main interests are the properties of refractory materials and failure analysis.

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DOI: 10.1595/147106706X153117

Rhodium and Iridium in Organometallic Catalysis WORK IN THE LABORATORY OF OUR RHODIUM BICENTENARY COMPETITION WINNER Robert H. Crabtree Department of Chemistry, Yale University, 225 Prospect St., New Haven, CT, 06520, U.S.A.; E-mail: [email protected]

Work to extend the catalytic chemistry of rhodium and iridium, with particular emphasis on the great versatility of the former, is outlined and summarised. Topics addressed include the design of chelating N-heterocyclic carbene ligands, and the cyclisation of alkynes using rhodium and iridium phosphine compounds as reagents or catalysts. The work was carried out by Ph.D. students sponsored through the prize awarded by Johnson Matthey to the winner of their Rhodium Bicentenary Competition.

In 2001, Johnson Matthey held a Rhodium Bicentenary Competition to commemorate the publication of the discovery of rhodium in 1804 by William Hyde Wollaston, the prize being the sponsorship of a Ph.D. studentship (1–3). Then Mr, now Professor Xingwei Li was the first to benefit from the Bicentenary Fellowship as a graduate student with the Crabtree group in the Yale University Chemistry Department (4). He went on to do postdoctoral work with John Bercaw at the California Institute of Technology (Caltech), and is now working in Singapore, having joined the Faculty in the Chemistry Department of Nanyang Technical University (NTU). Singapore is a rising power in science, and NTU was ranked 48th globally by the Times Higher Education Supplement in the 2005 ranking of the world’s best universities, and 26th among technology universities. It used to be the case that Chinese graduate students almost always stayed in the U.S.A. on graduation. However, in a healthy development, they are increasingly deciding to return to the Asia-Pacific region as the opportunities there become much more attractive. The second holder of the Johnson

Matthey Rhodium Bicentenary Fellowship with this group was Anthony Chianese, who went on to postdoctoral work with Michel Gagné at the University of North Carolina at Chapel Hill, and is now a Faculty member at Colgate University, Hamilton, New York, one of the leading liberal arts universities in the U.S.A.

Design of N-Heterocyclic Carbene Ligands Phosphines, particularly chelating phosphines, have been key to developing the catalytic chemistry of the platinum metals, but in recent years N-heterocyclic carbenes (NHCs), typically derived from deprotonation of imidazolium salts (Equation (i)), have shown great value as spectator ligands in catalytic chemistry (5, 6). Perhaps the most striking example is the great improvement in Grubbs’ metathesis catalyst obtained by introducing an NHC ligand (7). For the present, monodentate NHCs are mainly used, because of the lack of good methods to make chelating examples. Attempts using well-established synthetic routes often lead to the formation of 2:1 M:L complexes, each car-

(i)


171

(ii)

bene centre binding to a different metal centre. The problem here is that, unlike phosphines, NHC binding is only rarely reversible (6), so the kinetic 2:1 M:L products do not usually rearrange to the desired 1:1 chelates (Equation (ii)). Given the rising importance of NHCs, it is not surprising that the most highly cited result from the work of the two Johnson Matthey Fellows is a study (8) which provided an insight into how to design chelating NHCs to give the 1:1 or 2:1 complexes, as desired. In view of the origin of the award, the bicentenary of the discovery of rhodium, it is pleasing that rhodium produced optimal results in this study. Reaction of the bisimidazolium salt with strong base, as in the pathway of Equation (i), is problematic because the linker C–H bonds can also be deprotonated; so a selective procedure was necessary. The treatment of the imidazolium salt with silver(I) oxide (Ag2O) has proved (9) most useful for preparation of Rh(I) complexes suitable for subsequent catalytic testing. This involves intermediate formation of the Ag NHC complex, followed by transmetallation to Rh, as shown in Equation (iii) for a nonchelating case. In the event that the wingtip substituent at

nitrogen was n-butyl (8), the outcome of the reaction depended on the linker length, n. For short linkers (n = 1 or 2) the product was the 2:1 complex, but for longer linkers (n = 3 or 4) the product was the chelating 1:1 complex. A steric origin was suggested for the selectivity pattern. The NHC ligands have a bulky axis containing the linkers and the wingtip n-Bu groups, and a slim axis normal to the bulky axis. The preferred conformation of an NHC in square planar Rh(I) complexes has the NHC out-of-plane so that the bulky N-substituents occupy the empty sites above and below the square plane. For this to be achieved in a chelate complex, the linker must be long (Figure 1). The preferred conformation can be achieved in the case of a short linker only by the formation of a 2:1 complex, where each NHC is conformation-

Fig. 1 The preferred conformation of the NHC (left) is only achievable in a chelate with a long linker (right), where n is 3 or 4

(iii)


172

(iv)

(v)

ally independent. Other factors governing the reactivity have since emerged beyond the linker length; this study is still in progress. Moving to a direct metallation procedure (Equation (iv)), a 1:1 Rh(III) chelate complex was formed for all values of linker length, showing that chelation is in principle possible for the short linkers, and that the configuration adopted is a delicate function of the exact situation. The oxidation of the metal in Equation (iv) does not seem to depend on the presence of air; instead hydrogen is probably evolved to maintain redox balance. In later work (10, 11), these Rh(III) complexes and their iridium analogues have been shown to be excellent catalysts (up to 6000 turnovers h–1) for hydrogen transfer reduction of ketones by isopropanol (Equation (v)). By avoiding free hydrogen, this is sometimes considered a ‘green’ or environmentally more benign reduction procedure (12). These catalysts proved equally applicable to aldehydes and imines, substrates that

are less often encountered in prior reports. There was a surprisingly strong dependence of the activity on the nature of the wingtip substituent. Neopentyl, lacking a β-hydrogen, proved to be the best, perhaps because the presence of a β-hydrogen leads to Hofmann degradation of the substituent group.

Cyclisation of Alkynes Another piece of work, carried out by Xingwei Li in collaboration with Anthony Chianese under Johnson Matthey and U.S. Department of Energy sponsorship, involved reactions of alkynes using rhodium and iridium phosphine compounds as reagents or catalysts. Ironically, since this was a rhodium award, only iridium gave clean chemistry with worthwhile results. The work involved metalmediated reactions of alkynes involving either insertion into M–H bonds or attack by N and O nucleophiles (Equation vi). Acetophenone undergoes cyclometallation

(vi)


173

(vii)

(viii)

with the common Ir(III) precursor complex [IrH2(Me2CO)2(PPh3)2]BF4 to give the air- and moisture-stable catalyst, 1, which proves (13) to be effective for the exclusive endo-dig cyclisation of a variety of alkynylphenols and alkynylanilines (Equation (vi)). The reaction usually takes 2–3 h at 0.5–4 mol% catalyst loading at 20–110ºC. A number of prior catalysts (14, 15) also bring about this reaction, but with exo-dig or poor selectivity. Phenols, benzoic acids and anilines are also effective substrates, but the alkyne must be internal because terminal alkynes give a stable Fischer carbene complex instead, in which case there is no turnover. If the alkyne bears a hydroxy substituent, a spiroketal is formed (Equation (vii)). Transition metal catalysed hydroamination and hydroalkoxylation are both rather rare, especially with iridium, so a mechanistic study was carried out for the case of substrate 2a (Equation (viii)) to obtain some understanding of the key steps. The hydride ligand in 1 was unaffected, as shown by

retention of a deuterium label on catalyst cycling. Direct observation of the catalytic solution by 1H NMR spectroscopy revealed that catalyst 1 was completely converted to the amine complex 3. Furthermore, the order in substrate was zero, consistent with amine dissociation from 3 and reassociation of the substrate via the C≡C triple bond to 4 being the key step. Once a π-bound alkyne has been formed, nucleophilic attack becomes possible. Since the fragment to which the alkyne is bound has 16 valence electrons, the alkyne must bind as a 2 electron donor, not a 4 electron donor as is more usual (16). For the much less basic amine, 2b, the acetone complex 1 is the resting state of the catalyst and the reaction is now first order in substrate, consistent with binding only via the C≡C triple bond without unproductive binding via N. In a competition between 2a and 2b, the more strongly binding 2a inhibited reaction of the other substrate. Factoring out this inhibition, substrate 2b was intrinsically more reactive,

(ix)


174

(x)

suggesting that proton transfer from the NH group to the newly formed Ir–C bond may be the key step that traps the product (Equation (ix)). Alkyne coupling proved possible for terminal alkynes in a closely related system (Equation (x)) (17). Labelling studies showed that the reaction goes via an alkyne-to-vinylidene rearrangement. No catalytic version could be devised, however, because the butadienyl ligand proved too tightly bound. Oxidation is often difficult in organometallic chemistry, but in this case it proved possible to effect an oxidative intramolecular nucleophilic attack on the coordinated alkyne by a nitro group. The heterocycle in the resulting complex was extruded from the metal by treatment with CO to give the free heterocycle, anthranil (18) (Equation (xi)).

Remarks This work extends the catalytic chemistry of rhodium and emphasises its great versatility in this

respect. Development of the work will include appending molecular recognition functionality to the NHC ligand to bring about enhanced selectivity via a biomimetic strategy (19). Funding is often provided with the research results as the main object in view. Less often considered is the large multiplier effect which comes from the development of a student’s career that the funding makes possible. Over time, a student’s productivity – not to mention that of subsequent generations – is likely to dwarf the output from the initial funding. The future benefit does not often redound to the credit of the grantor, however, so it should be considered a signal public good. In this case, both Johnson Matthey Fellows have joined academic institutions and may well be influential in determining the future course of the field.

References 1 Platinum Metals Rev., 2001, 45, (2), 59 2 Platinum Metals Rev., 2001, 45, (3), 129 3 S. V. Ashton, Platinum Metals Rev., 2002, 46, (1), 2

(xi)


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4 R. H. Crabtree, Platinum Metals Rev., 2003, 47, (2), 73 5 W. A. Herrmann, C.-P. Reisinger and M. Spiegler, J. Organomet. Chem., 1998, 557, (1), 93 6 A. K. de K. Lewis, S. Caddick, F. G. N. Cloke, N. C. Billingham, P. B. Hitchcock and J. Leonard, J. Am. Chem. Soc., 2003, 125, (33), 10066 7 T. M. Trnka and R. H. Grubbs, Acc. Chem. Res., 2001, 34, (1), 18 8 A. R. Chianese, X. W. Li, M. C. Janzen, J. W. Faller and R. H. Crabtree, Organometallics, 2003, 22, (8), 1663 9 H. M. J. Wang and I. J. B. Lin, Organometallics, 1998, 17, (5), 972 10 M. Albrecht, J. R. Miecznikowski, A. Samuel, J. W. Faller and R. H. Crabtree, Organometallics, 2002, 21, (17), 3596 11 J. R. Miecznikowski and R. H. Crabtree, Polyhedron, 2004, 23, (17), 2857

12 J. S. M. Samec, J. E. Backvall, P. G. Andersson and P. Brandt, Chem. Soc. Rev., 2006, 35, 237 13 X. W. Li, A. R. Chianese, T. Vogel and R. H. Crabtree, Org. Lett., 2005, 7, (24), 5437 14 B. Gabriele, G. Salerno, A. Fazio and R. Pittelli, Tetrahedron, 2003, 59, (33), 6251 15 K. Hiroya, R. Jouka, M. Kameda, A. Yasuhara and T. Sakamoto, Tetrahedron, 2001, 57, (48), 9697 16 R. H. Crabtree, “The Organometallic Chemistry of the Transition Metals”, 4th Edn., Wiley, New York, 2005 17 X. W. Li, C. D. Incarvito and R. H. Crabtree, J. Am. Chem. Soc., 2003, 125, (13), 3698 18 X. W. Li, C. D. Incarvito, T. Vogel and R. H. Crabtree, Organometallics, 2005, 24, (13), 3066 19 S. Das, C. D. Incarvito, R. H. Crabtree and G. W. Brudvig, Science, 2006, 312, (5782), 1941

The Author Bob Crabtree, educated at New College, Oxford, U.K. with Malcolm Green, did his Ph.D. research with Joseph Chatt at Sussex and then spent four years in Paris with Hugh Felkin at the Centre National de la Recherche Scientifique (CNRS). He has been at Yale University since 1977, where he is now Professor. He has received several awards: A. P. Sloan Fellow, Dreyfus Teacher-Scholar, American Chemical Society (ACS) and Royal Society of Chemistry organometallic chemistry prizes, H. C. Brown Lecturer, Mack Award, Baylor Medal and Sabatier Lecturer. He has chaired the Inorganic Division at the ACS. He is the author of a textbook in the organometallic field, and editor-in-chief of the “Encyclopedia of Inorganic Chemistry” and “Comprehensive Organometallic Chemistry”. Early research on catalytic alkane C–H activation and functionalisation chemistry was followed by work on C–F bond activation, H2 complexes, M–H...H–O hydrogen bonding, and halocarbon and HF complexation. His homogeneous hydrogenation catalyst is in wide use.


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DOI: 10.1595/147106706X157744

CAPoC7: The State of the Art in Automotive Pollution Control PLATINUM, PALLADIUM AND RHODIUM CATALYSTS FEATURE IN DEVELOPING TECHNOLOGIES Reviewed by Jillian Bailie, Peter Hinde and Valérie Houel* Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, U.K.; *E-mail: [email protected]

The Seventh International Congress on Catalysis and Automotive Pollution Control (CAPoC7) was held from 30th August to 1st September 2006, in Brussels, Belgium. The Congress was attended by 300 participants from both academia and industry. Five half-day sessions addressed the state of the art in catalysis and automotive pollution control, and discussed technical perspectives and challenges in relation to present and future legislative regulations. The introductory session on European emissions legislation for mobile sources by R. Schulte Braucks (European Commission, Brussels, Belgium) set the scene by reminding the audience that the regulations are becoming more stringent. M. Khair (Southwest Research Institute, San Antonio, U.S.A.) in his talk on developments in diesel engine technology, highlighted the fact that some of the requirements for emission reductions can be met by engine development.

Particulate Control The area of particulate control was the focus for the first day’s talks. Jacques Lemaire of the Association Européenne d’Experts en Dépollution (AEEDA, Brussels, Belgium) presented the initial keynote lecture outlining the current situation. Reducing emissions of particulate matter is the focus of much research, whereas the amount and effect of NO2 emissions have been underestimated in formulating current legislation. The lecture, entitled ‘Diesel Exhaust Controls: a New Challenge for Diesel Oxidation Catalysts and Catalytic Soot Filters: Zero Production of NO2’ described three case studies of air quality in urban areas throughout Europe. The increase in NO2 levels over recent years was attributed to the introduction of continuously


regenerating trap (CRT®) and diesel oxidation catalysts (DOCs). The question of how catalysis can help solve the problem was raised, and it was concluded that the real challenges faced are not only technological. It is also imperative to ensure that suitable and timely legislation is in place, and that both the research community and industry have comprehensive development plans with efficient information exchange operating in order to meet future emission control requirements. The second keynote lecture, entitled ‘Highly Active and Potential Soot Oxidation Materials for Fuel Borne Catalysts and Catalysed Soot Filters’, was delivered by Professor Michiel Makkee (Delft University, The Netherlands). Makkee and coworkers investigated fuel-borne platinum group metal (pgm)-soot interactions with NO + O2. It was found that the Pt-soot showed the highest overall activity, followed by Pt-Ce-soot and then Ce-soot. The Pt-soot is most active for the oxidation of NO to NO2; however, the Pt-Ce and Ce showed the most efficient use of NO2 for soot oxidation. Makkee’s group also studied rare earth (RE) modified CeO2 catalysts (CeREOx with RE = La, Pr, Sm and Y) on soot filters. The results showed that the addition of Pr to the CeO2 gave the highest soot oxidation activity under both O2 and NO + O2 conditions. It was concluded that the increased activity results from the easier transport of oxygen to the surface of the soot, rather than from any mechanistic change, and that the bulk storage capacity was not an important factor affecting the soot oxidation over the catalysts tested. Makkee’s group showed that NO2 has a higher activity for the removal of soot than does O2. Therefore the oxidation of NO already present in the exhaust stream to NO2 is the preferred method of removing the soot present.

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Another of the oral presentations, delivered by G. Koltsakis (Aristotle University of Thessaloniki, Greece) was closely linked to Makee’s comments. Koltsakis and coworkers studied soot oxidation using Pt-based catalysts, and showed that there are two main effects of the Pt/Al2O3 during the oxidation of model soot under a flow of NO2 + O2, within the temperature range 300–450ºC. The first effect of the Pt is to promote the formation of atomic oxygen that can then be transported to the soot surface. The second effect is to reform the NO2 as it passes through the carbon-catalyst layer, which increases the overall oxidation of the carbon bed. It was also concluded that the use of NO, instead of NO2, was not detrimental to the soot oxidation, as the Pt was efficient at oxidising NO to NO2.

NOx Control The session on NOx control covered all three deNOx approaches: hydrocarbon selective catalytic reduction (HC SCR), NH3 SCR and NOx storage. In a keynote lecture in the introductory session, Professor R. Burch (Queen’s University Belfast, Northern Ireland, U.K.) compared HC SCR and NOx storage for low-temperature aftertreatment, focusing on the mechanism of both reactions. He put a strong emphasis on the necessity of testing real catalysts in real conditions. Hydrogen is known to improve considerably the deNOx activity of the Ag/Al2O3 catalyst with a range of reductants. Several posters discussed the SCR reaction mechanism on Ag/Al2O3 in the presence of H2. A variety of explanations were considered, such as formation of Ag clusters, destabilisation of nitrate or cyanide species, or creation of oxygenated species. There was also noticeable interest in the performance of lean NOx catalysts with alternative fuels (biodiesel, dimethyl ether (DME)). D. Yu. Murzin (Åbo Akademi University, Finland) presented results on the selective catalytic reduction of NOx over Ag/Al2O3 using various biodiesel compounds (methyl laurate and ethyl laurate) as reducing agents. They showed improved light-off temperature as compared with the equivalent alkanes. This


result has been attributed to the ether groups. The deNOx activity is also enhanced in the presence of hydrogen. The focus for NH3 SCR was mainly on mechanistic studies and modelling. The transient behaviour of Fe-exchanged zeolites was modelled for the sorption of ammonia, the reaction between NH3 and NO, and the influence of the NH3/NO ratio. This work was a collaboration between Umicore, Germany, and Technische Universität Darmstadt, Germany. The mechanism and modelling of a V-based commercial catalyst were addressed by C. Ciardelli and coworkers (Politecnico di Milano, Italy). A certain emphasis was placed on NOx storage catalysts, with several presentations and posters dedicated to this subject. In the first keynote lecture on deNOx catalysts, J.-D. Grunwaldt and U. Göbel (Umicore AG & Co KG, Germany) presented results on thermal ageing, and strategies towards reactivation of the Pt/Ba/CeO2 and Pt/Ba/Al2O3 NOx storage/reduction catalysts. After ageing of the catalyst, Pt sintering is believed to be responsible for the loss of low-temperature activity, whereas composite formation (such as BaAl2O4 and BaCeO3) due to reactions between the support and the storage component at high temperatures is generally believed to account for the loss in high-temperature activity. The aged catalysts could be reactivated by decomposition of BaCeO3 in the presence of H2O, NO2 and CO2. In the second keynote lecture on NOx control, X. Courtois (CNRS-Université de Poitiers, France) compared the NOx storage capacity, SO2 resistance and regeneration of CeZr-based NOx storage catalysts. Pt/Ba/CeZr presented the best storage capacity at 400ºC, according to basicity measurement by CO2 temperature programmed desorption (TPD), and Pt/CeZr showed the best performance at 200ºC, mainly due to its low sensitivity to CO2 at this temperature. For all samples, sulfating induced a detrimental effect on the NOx storage capacity, but regeneration at 550ºC under rich conditions led to the total recovery of catalytic performance. Several other presentations and posters generated an animated debate on the roles of the different components of the model

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Pt/Ba/Al2O3 catalyst: Ba intermediates (carbonates, nitrates, oxides, etc.) and Pt/Ba proximity.

Three-Way Catalysts, Mechanisms, Kinetics and Modelling Martyn Twigg (Johnson Matthey, U.K.) delivered a keynote lecture covering recent trends and future developments on three-way catalysts (TWCs), reminding the audience that gasoline spark-ignition engines still represent the major global market for passenger car applications, despite the growing diesel markets. The review examined the drivers for catalyst development, such as legislation, economic and technological factors, and emphasised the huge environmental benefits obtainable through the use of TWCs in terms of reduced tailpipe emissions. The impact of pgm prices as an economic driver for catalyst technology in terms of formulation development and lowering metal loadings was discussed. Future challenges for TWCs were outlined: further reducing tailpipe emissions, demanding OBD (on-board diagnostic) requirements, new engine types and the introduction of biofuels. Only one other oral presentation was given on TWCs: that of H. J. Kwon (Pohang University of Science and Technology, Korea). This concerned the effects of ageing on activity and selectivity on a dual monolith system; that is, a small Pd catalyst followed by a larger Pt/Rh/Ce monolith. Ageing resulted in a loss of CO oxidation activity for a Pd catalyst, and for a Pt/Rh/Ce catalyst, the selectivity for the NO-CO reaction was decreased, resulting in lower overall NOx reduction. On a different note to that of the preceding presentations on NOx storage, Professor Mike Bowker (Cardiff University, U.K.) gave an account of scanning tunnelling microscopy (STM) studies on model catalysts with the aim of understanding the structure of the BaO surface. In this case the ‘inverse’ catalyst method was employed. Here the BaO was deposited onto a single crystal Pt(111) surface. Bowker showed that it was possible to store NOx from a mix of NO and O2, and concluded that it was not necessary to have NO2 in the gas phase in order to store NOx. A Ba-peroxide species, metastable at 300°C, was discussed


as a possible surface species.

Miscellaneous Topics: Ageing, Poisoning and Alternative Fuels The final session of the meeting focused on ageing and poisoning. The range of topics covered included the regeneration of sulfur-poisoned Pd and Pt-Pd catalysts for methane combustion (in relation to natural gas fuelled vehicles), and thermal ageing and sulfur oxide effects on Pt-Pd diesel oxidation catalysts. The latter was the subject of the first official presentation to be given by the BASF Group in automotive catalysis following its acquisition of Engelhard, now incorporated as BASF Catalysts LLC.

Poster Sessions Over 100 posters were presented by both academic and industrial delegates during four viewing sessions. Additional time was allocated in the main programme for open discussions in greater depth – many of which were very lively. Much of the discussion and debate during these sessions focused on NOx-trap catalysts. The question ‘How does BaCO3 become nitrated?’ was raised. It was concluded that much work remains to be done to understand the mechanism.

Concluding Remarks Overall, CAPoC7 proved to be an enjoyable and informative congress. Many high-quality presentations, both oral and written, generated an advanced level of discussion. It is apparent that pgms remain at the forefront of many aspects of automotive catalysis. The congress also highlighted the need for good communication between industry and academia to ensure the efficient development of future technologies. The Reviewers Jillian Bailie is a Senior Scientist in the Gas Phase Catalysis Group at the Johnson Matthey Technology Centre (JMTC), Sonning Common, U.K. Her main interests lie in developing NOx reduction catalysts. Valérie Houel is a Senior Scientist in the Gas Phase Catalysis Group at the JMTC. Her main interests also lie in developing NOx reduction catalysts. Peter Hinde is a Research Scientist in the Gas Phase Catalysis Group at the JMTC. His main interests lie in developing catalysts for diesel oxidation.

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DOI: 10.1595/147106706X152703

The Platinised Platinum Interface Under Cathodic Polarisation MORPHOLOGY CHANGES UNDER THE INFLUENCE OF TETRALKYLAMMONIUM SALTS IN SUPER-DRY SOLUTION By Jacques Simonet Equipe MaCSE, UMR 6226, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France; E-mail: [email protected]

Under the use of super-dry dimethylformamide containing tetraalkylammonium salts (TAAX with X = Cl, Br, I, ClO, BF4, etc.) platinised platinum layers may exhibit a reversible charging process that occurs at quite negative potentials (more negative than –2.2 V vs. saturated calomel electrode (SCE)). The mode of reactivity of the electrolyte and the reversibility of the platinum charging of platinised layers (whatever the type of conducting substrate – gold and glassy carbon can also be used successfully) are discussed in terms of the nature of the salt. After cathodic charge and oxidation by air of samples removed from the cell, a huge change of morphology of the original platinised layer was observed. During repeated reduction/oxidation stages, the original amorphous platinised layer was progressively transformed, with a noticeable swelling of the original layer. This transformation, based essentially on cathodic swelling due to the peculiar reactivity of platinum in the presence of bulky tetraalkylammonium salts, is the precondition for a new kind of platinum interface.

Platinum is now considered one of the most practical materials for achieving electrochemical conversions (1, 2). In particular it can easily be cleaned to a polished surface, and employed in most electrocatalytic transformations, especially where adatoms deposited at the surface may induce a specific activity (3–13). Applications of the perfectly defined interfaces obtainable with platinum monocrystals are also noteworthy (14, 15). In the field of anodic processes, platinum is known (16) to be electrochemically stable even at very positive potentials. However, when platinum is employed as the cathode material, the situation is more complex (17): platinum indeed possesses a very low overpotential towards proton reduction, and this phenomenon seriously limits the accessible domain for achieving conversions of organic molecules when rather negative potentials are required. In general, beyond –1 V vs. SCE (saturated calomel electrode), hydrogen is frequently evolved (18–20). Thus even in organic solvents the level of moisture strongly limits the cathodic domain.


To circumvent the inconvenience of the low hydrogen evolution overpotential at platinum, the use of solvents of low proton availability has been developed. This may extend the cathodic domain by about 1 V. Given the desirability of reaching extremely negative potentials (e.g. –3 V vs. SCE, known to be easily obtained in organic solvents in the presence of tetraalkylammonium salts if a conventional mercury cathode is used), the application of “super-dry” media was developed (21, 22). Significantly dry media have been obtained by maintaining the solvent-electrolyte mixture over drying reagents such as strongly activated alumina. Extremely low moisture levels (often less than 50 ppm of water) have been attained. Unexpectedly, however, the use of platinum cathodes in contact with a super-dry solvent-electrolyte mixture brought to light (23–27) a form of ion insertion of (or reactivity with) the electrolyte (often an alkali metal or tetraalkylammonium salt) at the platinumsolution interface. Thus, in the presence of an electrolyte MX under conditions which effectively prevent hydrogen evolution at the platinum sur-

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face, the formation of a thin “ionometallic” layer of a general structure [Ptn–, M+, MX] could be demonstrated. Here n depends on the saturation level of the platinum layer and therefore on its maximum degree of reduction. In general, it was found that n = 2 for N,N-dimethylformamide (DMF) containing dissolved alkali metal iodides or bulky tetraalkylammonium halides (NR4+X–), according to Equation (i): nPt + e– + MX → [Ptn–, M+, MX]

(i)

In some respects, such a cathodic reaction of platinum with electrolytes – and the subsequent formation of an ionometallic layer – strongly resembles the formation of Zintl phases (28–30) via the reaction of an electropositive alkali metal with most of metalloids (such as Pb, Si or Ge). The classical synthesis of Zintl phases generally involves heating a mixture of these reagents in a closed tantalum or niobium vessel. Another reported method is the reduction of a salt of a post-transition metal in the presence of sodium metal in liquid ammonia (28, 29). Electrochemical methods may also be used (30–35): for example, cathodically polarised lead (or any other post-transition metal) immersed in a solution of a non-electroactive cation (such as K+) may produce a reduced polyanionic form as shown in Equation (ii): 4K + 4e + 9Pb → [Pb , 4K ] +

–

4– 9

+

(ii)

(Pb is the cathode material.) Similar phases have already been described (34, 35) with polarised mercury in the presence of tetraalkylammonium ions. However, the implication of the choice of anion in the electrolyte was never considered. Returning to platinum, the analogous electrochemical building of a complex layer owing to the involvement of ions concomitantly with the associated electron motion raises a number of issues (36, 37) about this new kind of interface: its stability, its conductivity, the reversibility of electron storage, the maximum attainable thickness as well as its reducing power. Additional factors to be taken into account include progressive distortion of the platinum lattice induced by the motion of


electrolyte cations, and progressive swelling evidently associated with the stoichiometry of insertion into platinum. The present paper aims to describe in terms of morphologic changes the cathodic behaviour of platinised platinum, which has been found to be much more reactive towards electrolytes than smooth platinum. This study focuses especially on the effect of tetraalkylammonium salts (TAAX) on the electrochemical reduction of platinum. An explanation of the effect of the TAA+ cation size on structural changes to the layer is proposed. In particular the behaviour of tetramethylammonium salts (TMAX) appeared anomalous. This behaviour provides information on the interfacial activity of the TMA+ ion, considered as the smallest nonacidic ammonium cation. Moreover, TMA+ cannot form an ylide through the Hoffmann degradation (38, 39). Also at non-reactive cathodes, the TMA+ ion has been reported as by far the most readily electroactive (39), meaning that the electrochemical reactivity of TMA+ could occur at a potential much less negative than those of other NR4+ ions, especially within a potential range where there is no appreciable reduction of residual water (even when present in significant amounts (> 500 ppm)).

Experimental Procedure Salts and Solvent

In most of the experiments, the concentration of TAAX (X = I, Br, Cl, BF4, ClO4) was 0.1 M. All salts studied were obtained from Fluka; their purity was at least 99%, and all were employed without any additional purification after being thoroughly dried under vacuum at 60ºC (except for TAAClO4 which, for reasons of safety, was used as received). Anhydrous DMF was obtained from SDS, France; its water content was claimed to be 0.005%. Nevertheless, DMF was maintained continuously over alumina activated at 340ºC in vacuo for at least four hours before solutions were prepared. All experiments were performed under an argon atmosphere, and the absence of dioxygen in the solutions was carefully checked. The continuous use of alumina (acidic, Brockmann I, standard grade from Aldrich) in solutions and in situ in the electrochemical cell during the experiments kept

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the moisture levels no higher than 50 ppm.

possible at its interface chemical reactions catalysed by strongly basic media.)

Electrochemistry All potentials are given with respect to the saturated calomel electrode (SCE), although measurements were obtained with a Ag⎪AgI⎪0.1 M TBAI system in DMF; this electrode, which is particularly suitable for scrupulously dry solutions, has a potential of –0.52 V vs. SCE at 25ºC. For voltammetry, a three-electrode cell was used without a separator. The counter electrode was a glassy carbon or graphite rod. Platinum working electrodes had a diameter of 1 mm. The working electrodes were polished with Norton polishing papers (grades 02 and 03) or DP Paste M made from monocrystalline diamonds (with particle size appropriate to the finest polishing). After polishing, the working electrode was sonicated for five minutes, rinsed twice with alcohol and acetone, and then dried at about 60ºC. Chronocoulometric and ECQM (electrochemical quartz microbalance measurement) procedures have been fully described in a recent paper (40). (Here the electrode acts specifically as a base provider, making

Electrode Plating Coulometric experiments were carried out with platinised platinum electrodes prepared by deposition of the metal from an aqueous solution of 10 g l–1 H2PtCl6 (Aldrich) in 0.1 M HCl onto a metal disk (effective area: 0.78 mm2). Gold was plated under the same conditions. Metal was deposited at a constant current density (30 mA cm–2). Morphology changes of the platinum layer during charging/discharging cycles were followed by SEM analysis after rinsing each sample with alcohol and acetone, and sonication to eliminate alumina particles.

Results

Voltammetry for Tetramethylammonium Salts Figure 1 (curve (b)) summarises the voltammetric response of smooth platinum under standard aprotic conditions. In 0.1 M TMAClO4 (as with other TMA+ salts), a diffusion step (IC) with a Fig. 1 Voltammetric responses of platinum electrodes in 0.1 M TMAClO4 in DMF. Super-dry conditions. Scan rate: 0.1 V s–1. Effective electrode area: 0.78 mm2. Potentials are referred to aqueous SCE: (a) Response of a platinised platinum electrode (two first scans) with a pause of 20 s at –2.8 V. Average thickness of the platinum deposit: 0.25 μm; (b) For comparison, the response of a smooth platinum electrode under the same conditions


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half-peak potential of about –2.2 V vs. SCE is observed in the course of the first scan. At more negative potentials (beyond about –2.5 V vs. SCE), the cathodic limit is reached. This limit is attributable to electrolyte decomposition. Both the potential and the current for the main cathodic step (IC) vary with the mode of polishing of the platinum and the moisture level of the electrolyte solution. If the solution contains much more than 200 ppm water, step IC is progressively shifted towards less negative potentials and becomes totally irreversible. Higher water content leads to a “cathodic wall” attributable to the water reduction. However, the current at step IC depends on the mode of polishing of the platinum electrode. Given particularly careful polishing (always under super-dry conditions), the magnitude of step IC may decrease, and it may even disappear. The nature of the surface, grain boundaries, as well as the possible presence of fractals and activated sites would be expected to favour an interfacial chargedischarge process. If the platinum interface described above is now platinised galvanostatically so as to produce a much larger active surface, the shape of the voltammetric curves, as shown in Figure 1(a), changes dramatically. For a relatively thick film of electrodeposited platinum (with, for example, an average thickness significantly greater than 0.1 μm), the use of a super-dry solvent-electrolyte enables a quasi-reversible step (IIC), at least in the

cases of TMAI, TMAClO4 and TMABF4 (Figures 1 and 2). For example, platinised platinum in 0.1 M TMAClO4 exhibits a pair of broad main steps (IIC and IA) whose half-peak potentials are E0.5pc = –2.0 V and E0.5pa = –1.7 V vs. SCE, respectively. At scan rates greater than 50 mV s–1, the relative areas of these two steps are approximately equal. At potentials more negative than –2.3 V vs. SCE, another cathodic step may arise. Its presence apparently depends on the history of the electrode surface and on the amount of platinum galvanostatically deposited onto the substrate. Limiting currents for step IIC (iII) do not depend directly, at a given sweep rate, on the amount of electrodeposited platinum. The platinising procedure shifts the main reduction step towards much less negative potentials, and the rate of the charging process (although not measured here) appears significantly greater at a platinised platinum surface. The shapes of these steps and their current values would suggest that only the external part of the deposit – then in contact with the liquid phase – reacts with the components of the electrolyte. With longer electrolysis times, a sudden decay of the cathodic current is observed at very negative potentials (Figures 1 and 2). This may be induced by a selfinhibiting phenomenon. This inhibition is attributable to the weak electronic conductivity of the ionometallic layer formed during the reduction process. Conceivably, compacting associated with a structural change in the platinised layer further

Fig. 2 Electrochemical behaviour of platinised platinum in 0.1 M TMABF4 in DMF. Super-dry conditions. Effective electrode area: 0.78 mm2. Average thickness of the galvanostatic platinum deposit: 0.3 μm. Scan rate: 0.1 V s–1. Two first scans. Reference electrode: aqueous SCE


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restricts the motion of species participating in this charging phenomenon. Pauses were introduced into forward voltammetric scans on both smooth platinum surfaces and substrates covered by very thin, strongly heterogeneous platings. In these cases, at very negative potentials (as shown in Figure 1(a)), the following scans towards negative potentials may be significantly altered. The total cathodic current is then strongly increased, and step IC completely disappears. Recurrent scanning and/or pauses in scanning would be expected to contribute to changes in the nature of the platinum surface. Thus the presence of only the pair of steps IIC and IA would suggest that smooth platinum zones at the electrode surface have disappeared under cathodic treatment. This could correlate with the observation that the presence of steps IC and IIC together depends on the conditions prevailing during the plating, and on the amount of electricity passed. Step IIC is observed alone in some cases; this could be attributable to changes in the plating homogeneity. For timescales much longer than those currently used for voltammetric experiments, the charging processes remained reversible, but generally showed current efficiencies lower than 60%. Figure 3 shows the two distinct branches in the chronocoulometric response of a platinised platinum microelectrode in a 0.1 M solution of TMAClO4 in DMF. The very steep slope at the beginning of the discharge process is notable; it is

associated with the thinness of the reduced film at the interface.

Voltammetry for Other Tetraalkylammonium Salts Voltammetric data obtained with bulky TAA+ salts (from tetra-n-butyl- to tetra-n-octylammonium salts) indicated much less reversibility than that already described for TMAX salts. The cathodic step IIIC (Figure 4) attributable to the reduction of platinum in the presence of the salt is shifted to more negative potentials. The corresponding anodic step IIIA is shifted in the anodic direction. Half-peak potentials are –2.4 V and –1.5 V vs. SCE respectively. The current of the anodic step is relatively small. At significantly more positive potentials, two reversible steps H1 and H2 may appear, even under super-dry conditions. These are readily assigned to the reversible anodic oxidation of hydrogen formed at very negative potentials at the polycrystalline platinum surface during the forward scan. The steps could not be induced merely by residual water reduction beyond –2.8 V. These steps were not observed with TMAX salts. Their presence tended to support the concept of a “probase” cathode (40) previously proposed for tetramethylammonium salts. On the other hand, it would be expected that large TAA+ ions under the conditions given here would produce hydrogen evolution, leading to reductive degradation of the salt. This may be regarded as a kind of cathodic Hoffmann reaction, Fig. 3 Chronocoulometric curve for a platinised platinum electrode of area 0.78 mm2 in 0.1 M TMAClO4 in DMF. Superdry conditions. Plating thickness: 0.2 μm. Charge at –2.3 V vs. SCE for 10 s followed by discharge at –0.5 V until nil current


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Fig. 4 Repeated voltammetric scans at a platinised platinum electrode of effective area 0.78 mm2 in 0.1 M TBAClO4 in DMF. Super-dry conditions. Average thickness of the platinum deposit: 0.4 μm. Scan rate: 0.5 V s–1. Potentials are with respect to aqueous SCE

in which the free electron plays the role of a base as shown in Equation (iii): R3N+CH2–CH2R′ + e– → R3N + CH2=CHR′ + ½H2

(iii)

In a parallel process, the expected two-electron cathodic cleavage of TAA+ (forming the anion R–) may trigger the classical Hoffmann degradation (protonation of the anion R– by the salt) – a partial explanation for the poor reversibility of the charging process. In overall terms, this type of degradation leads to a broadly similar product distribution, with the formation of a tertiary amine and an alkene. Only the hydrogen evolution (as proposed in Equation (iii)) appears specific to the behaviour of TAA+ at the platinum interface.

Microcoulometry Coulometric measurements were carried out at platinised interfaces in super-dry DMF-TAAX solutions. The conditions were close to those shown in Figure 3 (i.e. reduction beyond –2.4 V and oxidation at about –0.8 V), having reached saturation of the deposited layer. Only the amount of electricity recovered during the oxidation process


was taken into account. With tetra-n-butyl-, tetran-hexyl- and tetra-n-octylammonium halides, the stoichiometry was found to correspond to one electron per two atoms of platinum. This suggests a formula for the complex of the following form (Equation (iv)): [Pt2–, TAA+, TAAX]

(iv)

A large series of TMAX salts was tested (with X = ClO4–, BF4–, I–, Br– and Cl–), as well as the corresponding sulfate salt (Figure 5). It was confirmed that bare platinum as such does not rapidly accumulate a high charge within the timescale necessary for such processes (e.g. a few minutes). All coulometric experiments were conducted in very carefully dried DMF-electrolyte solutions. Complete dryness and neutrality of the platinised platinum electrode were ensured by rinsing with alcohol and/or DMF with the addition of Me4NOH, followed by double rinsing with acetone and drying. The gradient of the plot in Figure 5 reveals that four platinum atoms (abscissa) are correlated with the charge of one electron (ordinate), which supports the conclusion that the stoichiometry of the phase, after saturation within

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surface modifications and draw conclusions, the following parameters were considered:

– – –

Fig. 5 Microcoulometry of platinised platinum (area: 0.8 mm2) for different plating thicknesses. Charging at –2.2 V vs. SCE (reduction for 100 s, allowing full saturation of the deposit) and then oxidation at 0 V until nil current. Qd is the quantity of electricity recovered during discharge. Qf/4 is one quarter of the quantity of electricity required to convert PtIV to Pt0. Five TMAX salts were tested at 0.1 M concentration in DMF: + (X = Cl), (X = ClO4), Δ (X = Br), { (X = BF4), (X = I)

•

the timescale of charging, can be written as follows (Equation (v)): [Pt4–, TMA+, (TMAX)m]

(v)

Analysis of platinum microdeposits onto the gold substrate (via the EQCM technique) confirmed that m = 1.

the initial thickness of the platinum deposit;

the applied potential for the reduction; the theoretical amount of electricity per unit area required to charge (partially or totally) the platinised layer. After cathodic polarisation of the platinised samples, two alternative modes of oxidation were used and compared. The sample was either simply exposed to air after the electrolysis, or the sample was kept in the cell at a potential generally between –0.5 and +0.3 V vs. SCE until the current decayed completely. The present study describes only morphology changes caused by contact with air at the completion of the reduction process. Surface modifications were generally controlled so as to occur without any noticeable mass change. However, when thick deposits are over-reduced for a long time, charging of the platinum layer could possibly lead to a local collapse of the original plating. Figure 6 shows the original appearance of a platinised platinum sample before any cathodic treatment in the presence of salts. A few results have been selected as being the most representative from a large number of experiments demonstrating the huge modification of platinum surfaces by TAA+ salts under cathodic polarisation.

Modification of Platinum Films

Morphology Changes to Large Electrodes on Macroelectrolysis

In the absence of a visible degradation of the film (which was easily checked with a magnifying glass and confirmed by the absence of mass

A large number of potentiostatic electrolyses were performed in two-compartment cells on platinised sheets of commercial platinum in the presence of tetramethylammonium salts (TMAClO4, TMABF4 and TMAI), tetra-n-butyl ammonium iodide (TBAI), tetra-n-hexylammonium bromide (ThexABr) and tetra-n-octylammonium bromide (ToctABr). Experimental conditions were as described for the voltammetric and coulometric studies. The main point of these experiments was to use super-dry solvent-electrolyte; the addition of activated alumina to the cell appeared crucial to this. In order to compare the

Fig. 6 SEM image of a platinised layer galvanostatically deposited onto smooth platinum from H2PtCl6 solution in 0.1 M HCl . Current density: 5 mA cm–2. Total quantity of electricity: 1.6 C cm–2. Average thickness of plating: 0.4 μm


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changes), the amount of electrodeposited platinum could be related to the amount of electricity necessary to achieve the deposit. For example, by using the initial platinised layer shown in Figure 6, the original deposit was made with a quantity of electricity of 1.6 C cm–2 (total reduction of PtIV), which corresponds approximately to an average thickness of the deposit of δ = 0.4 μm. The reduction of the deposit at –2 V vs. SCE in the presence of TMAClO4 was performed until an amount of electricity of 0.8 C cm–2 was passed. This theoretically corresponds to twice the amount of electricity required for total saturation of the layer, given that the charging yield would be about 50% platinum. The stoichiometry is given by Equation (v) with m = 1. Cathodic polarisation was followed by oxidation, simply by contact of the samples with air during rinsing. The samples were then thoroughly sonicated. This electrochemical treatment resulted in a complex coverage consisting of more or less

touching platinum spheroids, with average diameter depending on the thickness of the initial layer. The average diameter is estimated at about 0.5 μm for the structure shown in Figure 7(a). Apart from the zones of spheroids, large flat zones were attributed to the original smooth platinum substrate. Similar morphologies were observed with platinised films, in particular with TBAI (See Figures 7(b) and 7(c)) and ToctABr (Figure 7(d)). However, with thicker platinised films, and with large amounts of electricity involved in the reduction process, the layer swells to different extents. (The layer swells by transformation into spheres during the cathodic reaction of platinum with bulky salts, as indicated by the stoichiometry of the ionometallic complexes.) The case of some TMA+ salts is, however, more complex. These afford relatively limited swelling in terms of the stoichiometry given by Equation (v). Primary spheres are covered by smaller spheroids,

Fig. 7 Reduction of thin platinised film in the presence of TAAX salts in DMF under super-dry conditions. After reduction, samples were rinsed and sonicated in contact with air: (a) Reduction in 0.1 M TMAClO4 of film of mean thickness 0.2 μm) at –2.5 V. Total amount of electricity: 0.8 C cm–2. Oxidation by air; (b) and (c) Reduction in 0.1 M TBAI of a platinum deposit of 0.22 mg cm–2 onto platinum substrate. Electrolysis at –2.5 V vs. SCE. Quantity of electricity: 1.7 C cm–2. No mass loss after oxidation by air, sonication and rinsing; (d) Reduction in 0.1 M tetra-n-octylammonium bromide. Deposit of platinum: 0.30 mg cm–2. Electrolysis at –2.5 V. Quantity of electricity passed: 1 C cm–2. No mass loss


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giving the overall morphology the appearance of a layer of blackberry-like structures. The uniform volume of all the spheres is also striking. (See Figure 8 for the case of TMAI.) The swelling may sometimes become chaotic, particularly where large amounts of electricity are involved. Large, regularly swollen cauliflower-like structures then arise (Figure 8). These are reminiscent of the structures observed during the anodic polymerisation of pyrrole or thiophene (41, 42), in which the polymers are rendered electrically conductive by the progressive insertion of anions as “dopants” inside the polymer matrix. In the present work, cauliflower and macrospherical structures were found, principally with thick platinised layers (Figures 9(a), 9(b) and 9(c)). During the oxidation of the platinised layer, movement of the salt out of the platinum causes a shrinkage, as clearly evidenced by the formation of large cracks (see Figure 9(d)) and large zones of uncovered

Fig. 8 Reduction (E = –2.5 V vs. SCE) of platinised platinum in 0.1 M TMAI. Thickness of platinum deposit: 0.2 μm. Moderate quantity of charge corresponding to half that theoretically required to saturate the platinised film. No mass loss. Two images of the layer at different magnifications; note the appearance of “cauliflowerlike”structures


platinum substrate (Figure 7(c)). The shrinkage of cathodically generated spheres under oxidation by air, due to the expulsion of ions, is strongly expected to yield almost empty structures. By contrast, the anodic oxidation of spheroid layers leads to profound changes, until a quasi-flattening of the platinum surface occurs (43) through the bursting of the spheres.

Discussion The use of tetraalkylammonium salts as electrolytes in aprotic (super-dry) DMF can undoubtedly lead to the reversible charging of platinised layers electrochemically deposited onto substrates such as platinum, glassy carbon or gold. The finely divided structure of platinised deposits apparently enhances the cathodic reactivity of platinum. Under these conditions, tetraalkylammonium salts (R4NX with R bulkier than Me) react cathodically with the platinum surface, but at potentials significantly more negative than those observed with R = Me. At such potentials, significant reduction of residual water may occur, and the charging process observed in conjunction with hydrogen evolution is always poorly reversible in terms of charge recovery. By contrast, cyclic voltammetric experiments carried out at platinised layers in the presence of cathodically more reactive TMA+ salts provide evidence for a quasi-reversible charge process. Thus, under super-dry conditions and for rather thick platinum deposits, the quantity of electricity specifically involved in the charging process was found to be an increasing function of the scan rate. Electrochemical charging is definitely first associated with the external part of the platinised layer. However, with sufficiently high currents and long electrolysis times, the platinum layer may become saturated with the electrolyte salt. The charge recovered during the re-oxidation process reaches a limit, and becomes proportional to the amount of deposited platinum. Thus a simple calculation performed for several TMA+ salts demonstrates that, at least with thin platinum films, the charging process involves four atoms of platinum for each transferred electron. All the ionometallic complexes obtained under

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Fig. 9 Formation of more chaotic structures of cauliflower-like morphology. (a) Reduction of a platinised layer of thickness 0.2 μm in 0.1 TMAClO4 at –2.5 V under weak current density, with a moderate total quantity of electricity; (b) Reduction of a platinised layer (0.30 mg cm–2) in 0.1 M tetra-n-octylammonium bromide with a large over-reduction of the layer. Part of the deposit then collapses; (c) Reduction of a platinised film of thickness 2 μm in 0.1 M TBABF4. A large quantity of electricity passed. Evidence for strongly swollen structures; (d) Same conditions as image (c). During oxidation by air, the film shrinks strongly and forms deep cracks

similar conditions with bulky NR4+ salts and alkali metal iodides exhibit reducing properties. They can therefore produce anion-radicals from π-acceptors such as fluorenone and 1,4-dinitrobenzene. Similarly, the reducing power of the layer was recently used to cleave diazonium cations, making possible the chemical functionalisation of the platinum surface (44). With TMAX, as stated above, the structure of the platinum layer at the saturation stage is quite different from those previously found (37) with bulky NR4+ (such as tetra-n-butyl-, tetra-n-hexyl-, and tetra-n-octylammonium salts). This difference seems to be due to the smaller size of the TMA+ cation producing a change in the spatial structure of the ionometallic complex. After cathodic polarisation of platinum and air exposure of the interface obtained in the presence of NR4+ cations, SEM images most frequently revealed either cauliflower-like structures or layers of spheres,


depending on such experimental parameters as the thickness of the platinised layer and the amount of electricity involved in the reduction process. The appearance of spheres of uniform size, as well as huge changes to the morphology of the original platinum layer are highly intriguing. Does the formation of spheres or swollen structures occur during the reduction process or later when the surface is oxidised by contact with air? Recent in situ electrochemical scanning tunnelling microscopy (EC-STM) experiments in this laboratory (45) revealed, particularly in the case of tetra-n-butylammonium iodide, that the reversible swelling of platinum monocrystals can be followed using cyclic voltammetry over relatively short durations. The swelling of platinum was found to be directly related to the cathodic reaction of surface platinum atoms with the electrolyte. The complete restoration of the surface at the end of the reverse scan was highly effective, at least for short reaction

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times and limited amounts of electricity. This finding strongly supports the conclusion that the platinum reactivity is fully reversible, at least in the case of tetra-n-butylammonium salts. Overreduced ionometallic layers in the presence of TMA+ (up to one TMA+ ion per platinum atom) could be reached in certain cases. Over-reduction of platings could cause spectacular swelling and deformation of platinum surfaces. Returning to the quasi-uniform size of the spheres (as shown in Figures 7 (a)–(d)), it may be proposed that these structures grow under thermodynamic conditions. (This assumption is supported by the quasi-reversibility of the electrochemical process). The total conformational energy per sphere, Esp, may be split into two terms, relating to the bulk (ρV) and surface (ρS) energies respectively as shown in Equation (vi): Esp = (4/3)πR3ρV – 4πR2ρS

(vi)

where R is the radius of the spheres. At the equilibrium (Equation (vii)): (dE/dR)eq = 4πR2ρV – 8πRρS

(vii)

The equilibrium radius, Req, of the spheres is given by Equation (viii): Req = 2ρS/ρV

(viii)

Thus the radii of the spheres depend only on energy factors specific to the experimental conditions (such as the nature of the salt used, its concentration, its level of dissociation, as well as the number of available platinum atoms). The formation of contiguous spheres of very similar volume suggests that the ionometallic layer turns out to be very mobile on the conducting substrate. Therefore the model of growth of swollen structures from randomly distributed activated centres onto the substrate surface is probably incorrect. A range of experiments were performed to visualise clearly the occurrence of the platinum swelling. The degree of swelling may be approximately estimated by adopting the following formula for the charged phase obtained with TMAX salts (Equation (ix)): [Pt4–, TMA+, TMAX]


(ix)

The example of TMAI is then taken as representative. On the basis of literature values of ionic radii for the phase constituents (43, 46), i.e., Pt = 0.80 Å, I– = 2.2 Å, and TMA+ = 3.01 Å, it is possible to assess the degree of swelling for closely-adjacent ions. This calculation predicts a volume increase of approximately 30 times – which is huge. Similar swelling factors can be estimated for X = ClO4– and BF4–. By contrast, the swelling at platinum without a specific insertion of the salt would be limited to 14 times – again in the case of TMAI, on attaining complete reduction of the platinum layer. Thus the deposition of a few platinum atoms onto a conducting surface would lead to the progressive formation of a sphere-like volume, until attainment of the final stoichiometry based on the availability of strongly reactive platinum atoms. Although the mode of swelling is unclear so far, the rate of growth of such spheres would be determined both by the number of starting points (perhaps randomly distributed on the surface) and the diffusion of ions. The mobility of the spheres on the platinum substrate (under the condition that an electric contact promotes their growth) should probably also be taken into account. Since the volume of the spheres is not directly dependent on the amount of platinum deposited, one can foresee the existence of zones weakly covered by a small number of spheres (see, for example, Figures 7(c) and 7(d)). It would be expected that the huge swelling described above starts from sites located at the interface between the platinised layer and the electrolyte solution, causing substantial volume changes and, in particular, the formation of spheres. A tentative approach is depicted in Scheme I. The charging process might involve a front of charge moving progressively from the external interface until it reaches the much less reactive platinum substrate. The formation of spheres or more complex and bulky structures by extrusion due to the swelling (cauliflower-like features for thicker platinum deposits, Figure 9) may explain some of the alterations to the electrode surfaces. If the ionometallic layer is oxidised simply by contact with air (presumably due to a slow electron transfer at the boundary of the spheres),

190

Scheme I Schematic representation of the morphology change of a platinised platinum interface (shown in green) during the charging process by TMAX followed by air oxidation. The ionometallic layer (the fully reduced form of the platinised layer) is shown in red. The oxidation by dioxygen would lead to smaller spongy spheres, of which the shrinking factor illustrated here is arbitrary

then the interface would be expected to keep roughly its original structure. The oxidation first forms a platinum shell, and continues by the diffusion of dioxygen through this shell. The action of dioxygen would tend to preserve the general features of the layer, including cracks and smaller spheres (often not immediately adjacent) owing to shrinkage. Scheme II depicts swelling processes on a much larger scale, which would lead to cauliflower-like structures in the case of thicker platinum layers and/or over-reduction of deposits.

Conclusions Under super-dry conditions, platinised platinum layers exhibit a high cathodic reactivity towards the electrolyte. In particular, with TMA+ salts, a fully reversible ion insertion has been demonstrated. A stoichiometry for this insertion process has been proposed for the condition that the platinised layer reaches is full reactivity. Coulometric results for a large number of TAAX salts strongly support the conclusion that two or four platinum atoms are associated with the transfer of one electron to produce thin modified

Scheme II Schematic representation for the swelling of the platinised platinum surface. Note the possible transformation of (c) for a moderate swelling into (d), obtained with larger amounts of electricity injected into the platinum layer (termed “cauliflower-like” structures in the text). Arrows indicate the supposed direction of the swelling


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(ionometallic) layers (up to 1 μm in thickness). Under appropriate conditions, the salt-infused ionometallic layer shows a huge swelling, which depends on the applied potential, the nature of the interface and the mode of the discharging process. With the aid of SEM techniques, it has been found that charging and discharging of platinum layers are correlated with their swelling and shrinkage. Dramatic structural changes of the platinised platinum layer have been analysed and explained in terms of both the existence of a reversible charging-discharging process and the specific nature of the electrolytes employed. Finally, analysis of reduction processes revealed that side reactions may occur, such as the slow decomposition of the ionometallic layer obtained at quite negative potentials. For example, methane may be evolved with TMAX salts as shown in Equations (x) and (xi): [Ptn– , TMA+, TMAX] → nPt + (CH3)3N + CH3• + TMAX

(x)

In the presence of a source of electrons and protons: CH3• → CH4

(xi)

Thus controlling the roughness of the platinum interface by the various treatments presented here might be used to impart particular properties to the resulting surface – for instance, by achieving a clean platinum surface in the absence of dioxygen, for catalytic and electrocatalytic applications.

Acknowledgments The author is grateful to the Centre de Microscopie Electronique à Balayage et MicroAnalyse (Dr Le Lannic, Université de Rennes) for its efficient help, and to Professor C. Amatore (ENS, Université de Paris VI) for fruitful technical discussions.

References 1 A. J. Bard and L. R. Faukner, “Electrochemical Methods: Fundamentals and Applications”, J. Wiley and Sons, New York, 1980 2 H. Lund, in “Organic Electrochemistry”, 4th Edn., eds. H. Lund and O. Hammerich, Marcel Dekker, New York, 2001, p. 243 3 R. Albalat, J. Claret, E. Gómez, C. Muller, M. Sarret and J. M. Feliu, J. Chem. Soc., Faraday Trans., 1990, 86, (10), 1845 4 L. D Burke and K. J. O’Dwyer, Electrochim. Acta, 1990, 35, (11–12), 1821 5 M. Shibata and S. Motoo, Hyomen Gijutsu, 1989, 40, (10), 78 6 V. N. Korshunov, V. A. Safonov and L. N. Vykhodtseva, Russ. J. Electrochem., 2005, 41, (9), 911 7 P. Ocon and J. Gonzalez Valesco, J. Appl. Electrochem., 1988, 18, (1), 43 8 Lj. V. Minevski and R. R Adzic, J. Appl. Electrochem., 1988, 18, (2), 240 9 R. R. Adzic, W. E. O’Grady and S. Srinivasan, J. Electrochem. Soc., 1981, 128, (9), 1913 10 B. F. Gianetti, C. M. V. B. Almeida, S. H. Bonilla, M. O. A. Mengod and R. Raboczkay, Phys. Chem., 2003, 217, (10), 35 11 H. A. Lyazidi, M. Moukhedena, M. Mestre and J. F. Fauvarque, Bull. Soc. Chim. Fr., 1995, 132, (10), 1039 12 J. M. Felui, E. Herrero and M. J. Llorca, Book of Abstracts, 210th ACS National Meeting, Chicago, IL, 20th–24th August, 1995


13 K. B. Kokoh, J.-M. Léger, B. Beden, H. Huser and C. Lamy, Electrochim. Acta, 1992, 37, (11), 1909 14 Y.-Y. Yang and S.-G. Sun, J. Phys. Chem. B., 2002, 106, (48), 12499 15 J. Clavilier, A. Fernandez-Vega, J. M. Feliu and A. Aldaz, J. Electroanal. Chem., 1989, 261, (1), 113 16 H. J. Schäfer, ‘Organic Electrochemistry’, in “Encyclopedia of Electrochemistry”, Volume 8, eds. A. J. Bard and M. Stratmann, Wiley-VCH, Weinheim, 2004 17 G. W. Morrow, in “Organic Electrochemistry”, 4th Edn., eds. H. Lund and O. Hammerich, Marcel Dekker, New York, 2001, p. 589 18 G. P. Klein, K. J. Vetter and J. W. Schultze, Z. Phys. Chem., 1976, 99, (1–3), 1 19 B. E. Conway and G. Jerkiewicz, Electrochim. Acta, 2000, 45, (25–26), 4075 20 J. Fournier, L. Brossard, J. Y. Tilquin, R. Côté, J.-P. Dodelet, D. Guay and H. J. Ménard, J. Electrochem. Soc., 1996, 143, (3), 919 21 O. Hammerich and V. D. Parker, Electrochim. Acta, 1973, 18, (8), 537 22 J. Heinze, Angew. Chem., 1984, 96, (11), 823 23 J. Simonet, E. Labaume and J. Rault-Berthelot, Electrochem. Commun., 1999, 1, (6), 252 24 C. Cougnon and J. Tanguy, unpublished observations 25 C. Cougnon and J. Simonet, J. Electroanal. Chem., 2002, 531, (2), 179

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26 C. Cougnon and J. Simonet, Electrochem. Commun., 2001, 3, (5), 209 27 C. Dano, Ph.D. Thesis, Université de Rennes 1, 1998 28 E. Zintl and G. Woltersdaf, Z. Electrochem., 1935, 41, 876 29 E. Zintl and W. Dullenkopf, Z. Phys. Chem., 1932, B16, 183 30 E. Zintl, J. Goubeau and W. Dullenkopf, Z. Phys. Chem., 1931, 154, (Abt. A), 1 31 J. B. Chlistunoff and J. J. Lagowski, J. Phys. Chem. B, 1997, 101, (15), 2867 32 J. B. Chlistunoff and J. J Lagowski, J. Phys. Chem. B, 1998, 102, (30), 5800 33 V. Svetlicic, P. B. Lawin and E. Kariv-Miller, J. Electroanal. Chem., 1990, 284, (1), 185 34 E. Kariv-Miller, P. D. Christian and V. Svetlicic, Langmuir, 1995, 11, (5), 1817 35 E. Kariv-Miller and P. B. Lawin, J. Electroanal. Chem., 1988, 247, (1–2), 345 36 C. Cougnon and J. Simonet, Platinum Metals Rev., 2002, 46, (3), 94

37 C. Cougnon, Ph.D. Thesis, Université de Rennes 1, 2002 38 A. Merz and G. Thumm, Justus Liebigs Ann. Chem., 1978, 1526 39 C. E. Dalm and D. G. Peters, J. Electroanal. Chem., 1996, 402, (1–2), 91 40 J. Simonet, Electrochem. Commun., 2003, 5, (6), 439 41 A. F. Diaz, K. K. Kanazawa and G. P. Gardini, J. Chem. Soc., Chem. Commun., 1979, (14), 635 42 G. Tourillon and F. Garnier, J. Electroanal. Chem., 1982, 135, (1), 173 43 “Handbook of Chemistry and Physics”, 46th Edn., CRC Press, Cleveland, OH, 1965–1966, F 117 44 J. Ghilane, M. Delamar, M. Guilloux-Viry, C. Lagrost, C. Mangeney and P. Hapiot, Langmuir, 2005, 21, (14), 6422 45 J. Ghilane, M. Guilloux-Viry, C. Lagrost, P. Hapiot and J. Simonet, J. Phys. Chem. B, 2005, 109, (31), 14925 46 Y. H. Zhao, M. H. Abraham and A. M. Zissimos, J. Chem. Inf. Comput. Sci., 2003, 43, (6), 1848

The Author Emeritus Professor Jacques Simonet is Directeur de Recherche, Electrochemistry Group, Université de Rennes, France. His principal interests are organic electrochemistry, the activation of organic reactions by electron transfer, electro-polymerisation and the formation of redox polymers. He also researches on the reversible cathodic charging of precious metals (platinum and palladium) in super-dry conditions, in contact with polar organic solvents containing electrolytes, mimicking Zintl phases for transition metals.


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DOI: 10.1595/147106706X150543

SURCAT 2006 Conference THE ANNUAL CONFERENCE OF THE ROYAL SOCIETY OF CHEMISTRY SURFACE REACTIVITY AND CATALYSIS GROUP Reviewed by S. E. Golunski Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, U.K.; E-mail: [email protected]

SURCAT 2006 was held at the University of Cardiff from 25th to 27th July 2006. Thirty-three years after Professor Wyn Roberts organised the first Surface Reactivity and Catalysis Group meeting, this annual event is still going strong. In spite of global competition from conferences with identical or closely related themes, SURCAT 2006 attracted over a hundred delegates, mostly from the U.K. home countries (England, Northern Ireland, Scotland and Wales) – with the U.K. academic centres of excellence in catalysis being particularly well represented. For an international conference, SURCAT 2006 must have left an impressively small carbon footprint! A strong cast of speakers from laboratories around the world provided the international dimension and gave the conference an outward-looking feeling. The range of catalytic materials discussed was relatively wide ranging, but the precious metals, particularly gold and the three key platinum group metals (platinum, palladium, rhodium) were undeniably the centre of attention.

Supported Catalysts Opening the first session, Professor Bruce Gates (University of California, U.S.A.) described an integrated approach to the study of the active phase, support material and reactive intermediates in heterogeneous catalysis. He uses synthetic methods to deposit metal species on real support materials, avoiding standard impregnation routes that can leave the surface contaminated with trace impurities. These methods allow Gates to control the oxidation state of the active metal and, in some cases, to deposit complexes in which the ligand is designed to be an intermediate in the catalytic reaction. He has made a range of supported gold complexes that catalyse the oxidation of CO at low temperature, with the activity showing a correla-


tion with the surface concentration of cationic gold. However, Ton Janssens (Haldor Topsøe, Denmark) showed that conventional supportedgold catalysts conform to the model in which maximum CO-oxidation activity coincides with an optimum Au0 particle size. In fact, the particle size per se is not as critical as the associated particle geometry. In Au/TiO2 and Au/MgAl2O4, the activity seems to relate directly to the number of corner atoms on the metallic gold particles.

Selective Oxidation Though CO oxidation has become established as a benchmark reaction for screening gold catalysts, their ability to catalyse selective oxidations is now seen as a more exploitable quality. Taking the conversion of glucose to gluconic acid as his model reaction, Professor Michele Rossi (University of Milan, Italy) has been studying liquid phase oxidations using colloidal gold as the catalyst. He sees a linear correlation between rate and the total number of exposed gold atoms. The particles have intrinsically high selectivity and turnover frequency, comparable to those of enzymes, and cannot be promoted by adding typical catalyst support materials to the colloid. Professor Graham Hutchings (Cardiff University, Wales) broadened the range of selective oxidation reactions by discussing the preferential oxidation of CO in the presence of excess H2, and the direct synthesis of H2O2 from H2 and O2. By fine tuning the calcination temperature of supported gold, highly selective catalysts can be produced that can convert 99.95% of the CO in reformate in a single step. In peroxide synthesis, the challenge is to design high performance catalysts that will operate in a dilute gas-feed, outside the explosive limit. The Cardiff group has developed highly active and selective Au-Pd formulations, which are stable, reusable and do not

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require the usual bromide or phosphate promoters. Hutchings showed some beautiful TEM images (produced by Lehigh University, U.S.A.) revealing a core-shell particle structure, with the palladium completely encasing the gold.

Alkyne Hydrogenation The delicate balance between complete and partial hydrogenation of alkynes over relatively simple palladium catalysts (for instance, 1% Pd on carbon) reflects different steady states during their operation. David Lennon (University of Glasgow) showed that there is a step change in both activity and selectivity during propyne hydrogenation as the H2:hydrocarbon ratio is increased. He explained this in terms of two different active sites formed on the palladium surface during exposure to the reactants. At low H2:hydrocarbon ratios, a high surface coverage of hydrocarbon-like species results in exposed sites that can only be accessed by propyne and H2; at high ratios, more of the surface is exposed and complete hydrogenation can occur. In the case of acetylene, Shamil Shaikhutdinov (Fritz-Haber Institute, Germany) attributed changes in selectivity to the nature of the adsorbed hydrogen species. Partial hydrogenation to ethylene occurs by reaction with surface species, but the consecutive step to ethane requires subsurface hydrogen. The formation of the subsurface species can be suppressed by adding silver to the palladium.

Water Gas Shift Water gas shift is a deceptively simple reaction, for which each new catalyst seems to pose a fresh challenge when it comes to unravelling the surface mechanism. Sergiy Shekhtman (Queen’s University Belfast) has used temporal analysis of products to study Pt/CeO2, which is notable for matching the activity of conventional Cu-Zn-Al catalysts, but has the advantages of being nonpyrophoric and not being deactivated by exposure to air. Following pretreatment of Pt/CeO2 with H2O, CO-pulsing experiments show a deficit in the amount of CO2 formed compared with the amount of CO consumed. This implies that the predominant mechanism for water gas shift is not


based on a simple redox cycle, but involves a common intermediate formed from CO and H2O.

Epoxidation of Ethylene A similarly rigorous study has allowed Professor Ken Waugh (University of Manchester) to identify the key intermediate in the epoxidation of ethylene on silver catalysts. Best described as a surface oxametallacycle, it consists of an H2CO–CH2 species bridging two silver atoms. Ethylene adsorption on a series of pretreated Ag/Al2O3 samples reveals that the presence of surface chlorine promotes the reaction by weakening the Ag–O bond in the oxametallacycle, so freeing the terminal oxygen to form the epoxy group of the product molecule.

Catalyst Coking In some parts of the world, such as China and Singapore, methane dehydroaromatisation is being considered as a means of converting natural gas to higher value chemicals. Taking a different view of the same reaction, Justin Hargreaves (University of Glasgow) sees it as a potential route to CO-free hydrogen. Using Mo-impregnated ZSM5 zeolite as the catalyst, the product stream has a much higher H2:benzene ratio than expected. The carbon balance is completed by taking into account the coke deposited on the catalyst. Whereas the group at Glasgow is just beginning to probe the nature of this coke, Geomar Arteaga (Aberdeen University) described a well advanced study of similar effects on platinum catalysts. When Pt/Al2O3 is exposed to pyrolysis gasoline, very rapid coking takes place, leading to the formation of two different deposits. ‘Soft’ coke has a relatively high hydrogen content and is removed by oxidation at moderate temperature, whereas ‘hard’ coke is more carbon-like and requires a much higher oxidation temperature. Although blocking active sites, the coke modifies the platinum surface, leading to the suppression of hydrogenolysis reactions and the promotion of aromatisation.

Vanadium Catalysts Vanadium-based catalysts are very topical, cropping up in a seemingly diverse range of appli-

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cations. Sreekala Rugmini (University of Glasgow) showed that, for the direct dehydrogenation of butane, the best performance of V/Al2O3 coincides with a high surface concentration of two-dimensional polyvanadate domains. This optimum surface state is achieved at a vanadium loading of 3.5%. At lower loadings, monomeric vanadia species promote the formation of coke; at higher loadings, the activity declines as V2O5 crystallites are formed. In the case of butane oxidation to maleic anhydride, Taufiq Yap (Universiti Putra Malaysia) has improved the preparation of V-P-O catalysts with a mechanochemical step: ball-milling the hydrated VOHPO4 precursor in solvent so as to alter the microstructure of the finished catalyst.

Fresh Approaches in Well-Trodden Fields Two presentations provided fresh approaches in some well-trodden fields. As Professor Rob Brown (University of Huddersfield) pointed out, temperature programmed desorption of ammonia is routinely, but often uncritically, used to measure the acidity of catalysts. Brown has developed an ammonia-pulsing technique, which allows the concentration and strength of acid sites to be determined calorimetrically. The technique is subtle enough to exclude the contribution from ammonia adsorbed on non-acidic sites. The Huddersfield group has used it to study some of the ‘designer’ catalysts and support materials, including polystyrene sulfonic acid resins and Nafion. In the field of chiral catalysis, the ultimate aim is to achieve an enantiopure product. Paul Kilday (University of Aberdeen) has used the novel approach of adding ionic liquids to the reaction medium, during the Pt-catalysed hydrogenation of alkyl pyruvates in the presence of cinchonidine. In some instances, the enantioselective excess is improved by almost 20%.

Future Prospects As with all the best conferences, SURCAT 2006 highlighted the hot topics, the recurrent issues, and the likely future trends. With the aid of some spectacular images, Professor Chris Kiely (Lehigh University, U.S.A.) showed us the shape


of things to come in electron microscopy, where it is becoming possible to determine composition and morphology on a particle-by-particle basis. At the same time, the long-standing ‘material gap’ between surface science and catalysis is being bridged by the design of industrially realistic model catalysts. Using real precursors, Professor Hans Niemantsverdriet (Eindhoven University, The Netherlands) has produced flat model chromium catalysts on silica wafers, which are ideal for study by surface science techniques. His dream is to be able to observe a single active site in action! Undoubtedly, though, the most futuristic ideas on catalyst design and catalyst applications came from Professor Richard Lambert (Cambridge University). By using a bifunctional ligand as an axle for a porphyrin molecule, he has been able to produce a nanoscopic rotor – the first component in a catalytic nanomachine?

Conclusion It was highly appropriate that the closing remarks were made by Professor Roberts, who asked the question ‘What has changed since the first SURCAT conference?’. Well, the catalytic building blocks are still very similar – the platinum group metals, reducible metal oxides and gold were all on the agenda in 1973. Perhaps the most striking difference is in the array of tools now available for the study of catalysis. A major theme of the first conference was the use of surface reflectance infrared spectroscopy, which heralded the development of the techniques that we now describe as in situ and operando. Perhaps, in terms of impact, the modern equivalent is high-resolution electron microscopy, which is taking us ever closer to understanding the relationship between the active site and its surface environment. The story will no doubt be continued at SURCAT 2007, which will be held at The University of Manchester. The Reviewer Dr Stan Golunski is Technology Manager of Gas Phase Catalysis at the Johnson Matthey Technology Centre. Since joining the company in 1989, he has worked on fuel reforming, process catalysis, and catalytic aftertreatment for internal combustion engines.

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DOI: 10.1595/147106706X154882

Reliability of Platinum-Based Thermocouples INFLUENCES OF CONTAMINANTS AND OPERATING ATMOSPHERE By Roy Rushforth Charles Booth Ltd, 49–63 Spencer Street, Birmingham B18 6DE, U.K.; E-mail: [email protected]

A series of articles in this Journal by Wilkinson on platinum-based thermocouples and their use (1–4) addressed most of the potential problems and performance-limiting factors. The author referred to the possibility of deterioration of thermocouple performance through contamination. This article expands on this, demonstrating that the prevailing atmosphere in which the thermocouple is operating can have a profound effect on its life and accuracy.

In his article on minimising thermocouple drift (2), Wilkinson referred to the possible effects of contaminants, and recommended cleaning each limb of the thermocouple thoroughly prior to use. This is excellent advice, and will help to reduce the potential for subsequent performance deterioration. However, despite the best efforts to keep the system clean, it is still possible for performanceaffecting contaminants to be introduced into the thermocouple.

Refractory Insulators In practice, thermocouples are fitted with refractory insulation between the two limbs (5). Either the limbs are threaded through insulators, or they are surrounded by compacted refractory (as in a metal sheathed unit). In either, alumina has been the most frequently used refractory. The premise here is that platinum and its alloys can be heated in contact with the more refractory oxides, including alumina, without deleterious effect. Indeed platinum thermocouples have shown great stability in contact with alumina at temperatures up to 1600ºC for 1000 hours, in a variety of atmospheres, including high grade argon with an oxygen content of only 50 ppm. This long-established view of the stability of platinum in contact with refractory oxides must however be tempered by the knowledge that this apparent inertness is not invincible. The mechanisms by which some contaminants can be introduced into the platinum thermocouple, subsequently to affect its performance, can be complex. They involve the active participation of the refrac-


tory insulation material. At high temperatures, particularly above about 1300ºC, the potential for such processes to occur, under specific conditions, can increase. Serious platinum limb contamination and even catastrophic failure of the unit can result.

Platinum–Refractory Reactions So what are these specific conditions? The nature of any potential reactions between the platinum and the refractory must first be understood. Alumina is generally considered a very stable oxide – after all, as bauxite, it is one of the most prevalent natural sources of aluminium. It dissociates as follows: 2Al2O3 ' 4Al + 3O2

(i)

In air, as the temperature is increased the equilibrium shifts from right to left, i.e. the stability of alumina increases. This remains true even when oxygen levels are reduced, for instance, by the use of a vacuum or argon/nitrogen/hydrogen/cracked ammonia atmospheres. However, if platinum is introduced into the system, with an aluminasheathed platinum versus rhodium-platinum thermocouple, the renowned stability of alumina can be undermined. The phase diagram for the platinum-aluminium system (6) confirms that at the platinum-rich end, intermetallic compounds are formed – generally readily; the process is exothermic and typical of those where intermetallic compounds are formed. The resultant product, probably Pt3Al in the first instance, is very stable. Thus at high temperatures, if the partial pressure of oxygen in the working atmosphere is

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reduced, and is maintained so, the potential increases significantly for two reactions to occur to the detriment of thermocouple performance: 2Al2O3 → 4Al + 3O2

(ii)

(Oxygen is removed by the ambient atmosphere.) 3Pt + Al → Pt3Al

(iii)

(A stable intermetallic compound is formed and heat is evolved.) Darling et al. studied these reactions in some detail in the early 1970s, (7–10) with respect to a number of refractory materials such as alumina, thoria, boron nitride, hafnia, zirconia and magnesia. (Boron nitride and hafnia are not referred to in References (7–10) but were included in the original investigation.) Thorium, boron, hafnium and zirconium will, similarly to aluminium, form intermetallic compounds with platinum given appropriate conditions. Darling et al. demonstrated that intermetallic reactions are possible with these refractories, in fact extremely probable, at temperatures above about 1300ºC, once the oxygen potential of the ambient atmosphere is maintained at a reduced level. Such levels were shown to be achievable by evacuation using a conventional roughing/diffusion vacuum pump system down to 10–3 Pa pressure or by the use of hydrogen-containing atmospheres where oxygen removal was ‘continuous’, as found in many high-temperature melting or heat treatment furnaces. If silica, or a silicon-containing compound, is present, for instance a silicate-containing alumina, the reaction potential is further increased through the very strong affinity between platinum and silicon (10). The resultant Pt/Si compound has a very low melting point – less than 1000ºC; therefore once the compound has formed in the limb of the thermocouple, catastrophic failure through incipient fusion will occur once this temperature has been exceeded.

Preconditions for Adverse Reactions The timescale for such reactions depends strongly on the efficiency of oxygen removal. In a continuously maintained vacuum, the reaction will progress quite slowly, and it is unlikely that any sig-


nificant detrimental effects will occur before at least 100 hours usage at temperatures in excess of 1300ºC. In extreme instances, where strong reducing conditions prevail, ensuring very low oxygen levels, such reactions will occur quickly, within a few hours. Even then, compositional changes in the platinum limb would only adversely affect thermocouple accuracy if they occurred in that part of the unit located in the thermal gradient. Any contamination occurring in that part of the thermocouple held in the stable hottest zone of the furnace would not affect accuracy. Catastrophic failure through incipient melting of the intermetallic products could occur where the furnace running temperature exceeds the melting point of the compound. Such failures have been observed in a platinum thermocouple limb after reaction with alumina at 1450ºC (10). There is one exception to vulnerability to reduction and intermetallic reactions among the commonly available refractories, namely magnesium oxide (magnesia). Given the absence of ‘the usual suspects’ such as silicon, it is extremely difficult to promote significant dissociation of magnesia and the formation of platinum-magnesium compounds, even in the most aggressive oxygen removal environments at temperatures up to 1700ºC. The affinity between platinum and magnesium is very low, and there is therefore no thermodynamic driver for them to react to form stable compounds. It is important to remember that these reactions can only continue in environments where the oxygen is continuously removed; once the partial pressure of oxygen increases, the reaction will slow down and eventually cease as the equilibrium partial pressure is attained. Therefore one would not expect deleterious breakdown of a dispersed oxide phase such as zirconia in, for instance, a dispersion-strengthened platinum product, since dissociated oxygen cannot normally be continuously removed. However, it has also been shown that silica can be reduced simply by the presence of oil, via, for example, an oil-soaked refractory particle being rolled or drawn onto the surface of the platinum (10). At high temperatures a very local reducing environment is created by the oxidation

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of the oil, promoting the dissociation of the silica, and the exothermic reaction of the silicon with the platinum to form a platinum silicide.

Specification and Maintenance of Thermocouples The selection of the appropriate refractory insulation material is clearly very important. For instance, a range of ‘grades’ of alumina insulator are available, some containing quite high levels of silicates, while others consist of virtually pure alumina. At low operating temperatures, say below 1000ºC, the potential for contamination between thermocouple and insulator will be small, and alumina insulators of lower specification can be used. At higher temperatures, particularly above about 1300ºC, the presence of silicates and other impurities can increase the potential for contamination and subsequent catastrophic failure of the unit, depending on operating conditions. It is possible that thermocouples fail or lose accuracy in service, particularly during long-term, high-temperature usage, more often than is realised through the reactions described here. Paraphrasing Wilkinson’s point, ‘cleanliness is next to godliness’ if optimal performance is to be obtained from the thermocouple. However, the user must also be fully aware of the conditions under which the thermocouple is to be used, to

ensure that these reactions do not occur to the detriment of its performance. Clearly, where the prevailing environment might either very locally or generally tend towards low oxygen/reducing conditions, and if a conventional unit is to be employed, then the user must consider carefully the thermocouple/refractory combination, the quality of the refractory and the prevailing operating atmosphere. In such instances, the use of a metal sheathed thermocouple, although these have their own drift problems (2), would at least prevent thermocouple/refractory reactions from occurring.

References 1 2 3 4 5 6 7 8 9 10

R. Wilkinson, Platinum Metals Rev., 2004, 48, (2), 88 R. Wilkinson, Platinum Metals Rev., 2004, 48, (3), 145 R. Wilkinson, Platinum Metals Rev., 2005, 49, (1), 60 R. Wilkinson, Platinum Metals Rev., 2005, 49, (2), 108 L. Michalski, K. Eckersdorf, J. Kucharski and J. McGhee, “Temperature Measurement”, 2nd Edn., John Wiley & Sons Ltd, New York, 2001 “Binary Alloy Phase Diagrams”, 2nd Edn., eds. T. B. Massalski, H. Okamoto, P. R. Subramanian and L. Kacprzak, ASM International, Ohio, U.S.A., 1990 A. S. Darling, G. L. Selman and R. Rushforth, Platinum Metals Rev., 1970, 14, (2), 54 A. S. Darling, G. L. Selman and R. Rushforth, Platinum Metals Rev., 1970, 14, (3), 95 A. S. Darling, G. L. Selman and R. Rushforth, Platinum Metals Rev., 1970, 14, (4), 124 A. S. Darling, G. L. Selman and R. Rushforth, Platinum Metals Rev., 1971, 15, (1), 13

The Author Roy Rushforth is Managing Director of Charles Booth Ltd (part of the Stephen Betts Group), a U.K. dental alloy manufacturer supplying precious and non-precious materials for crown and bridge restorations. His 40 years experience in platinum group metals and gold has been first at Johnson Matthey, where he completed a major project for the Atomic Energy Authority at Harwell investigating platinum-refractory stability. He later developed new alloys and processes for the Johnson Matthey jewellery and dental businesses. He then worked at the Birmingham Assay Office, U.K., as Development Director, before joining Charles Booth in 2000.


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DOI: 10.1595/147106706X158789

“Principles of Fuel Cells” BY XIANGUO LI, Taylor & Francis, New York, 2005, 572 pages, ISBN 978-1-59169-022-1, £50.00, U.S.$125.00

Reviewed by Tom R. Ralph Johnson Matthey Fuel Cells, Lydiard Fields, Great Western Way, Swindon SN5 8AT, U.K.; E-mail: [email protected]

This new book by Xianguo Li attempts to cover both the fundamental aspects associated with the thermodynamics and the electrochemical processes in the fuel cell, with a review of the development of the six major fuel cell types. Chapter 1 provides a sound introduction to fuel cells, covering the main points in terms of the operating principles and the typical classification of the different types of fuel cells, by electrolyte or operating temperature, as a prelude to tackling first the fundamentals and then the technology of fuel cells.

Target Audience and Fundamentals The author identifies the main audience as undergraduate senior-level and first-year graduate students in the engineering disciplines. It is perhaps no surprise that a key strength of the book is the thorough treatment of the thermodynamics of the fuel cell in Chapter 2. The worked examples are especially helpful in understanding a subject area that many students struggle to comprehend. The treatment of the electrochemical losses in Chapters 3 and 4 reflects the current level of understanding of this difficult area. The electrochemical kinetic losses are perhaps more clearly dealt with in other electrochemistry books (1), but the coverage of the concentration overpotential in terms of both a simplistic and a more rigorous engineering approach to mass transport losses near the limiting current, with worked examples, is particularly well done. These chapters on fundamentals do provide the engineering student with a solid basis for tackling fuel cell technology at a higher level. The remaining chapters deal with the different fuel cell types. While pitched at the correct level for students, practising engineers or other professionals would also benefit from a more comprehensive treatment of the current state of the art of fuel cell technology (see for instance, (2)).


Major Fuel Cell Types At twenty pages, the treatment of the alkaline fuel cell (AFC) in Chapter 5 is perhaps a little excessive, given that this technology is limited to space applications. This is because the lack of CO2 rejection by the electrolyte, even at the level of ca. 300 ppm found in air, produces a significant performance loss. The discussion of the impact of operating conditions on the performance of the AFC is nevertheless educational, and the general approach is applicable to all fuel cell types. In contrast to the AFC, the phosphoric acid fuel cell (PAFC) dealt with in Chapter 6 has met the 40,000 h operational lifetime criterion, if not the cost targets, required for the 200 to 300 kW stationary cogeneration market. The PAFC is the most commercially developed fuel cell type. Most of the important areas of the technology are touched upon in Chapter 6, including the durability issues, although more detail on the construction and performance of the cell materials could have been added, along with a more detailed discussion of natural gas reforming. In Chapter 7 the proton exchange membrane fuel cell (PEMFC) receives by far the largest attention of all the fuel cell types, reflecting the focus placed on the PEMFC over the last two decades. There is a decent review of the different flow field designs employed by stack developers and academic researchers, and a fairly expansive discussion of the membrane electrolyte based on the Nafion® material developed by DuPont de Nemours. The membrane structure, water sorption properties, protonic conductivity and the water movement mechanisms are highlighted. The development of the membrane electrode assembly (MEA) is broached in several sections of the chapter. The different fabrication routes and the importance of carbon supported catalysts, with impregnation of the platinum catalyst layer with proton conducting electrolyte to improve catalyst utilisation, are clarified.

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The design of the anode for improved reformate (CO and CO2) tolerance is discussed in detail, with the importance of platinum-ruthenium (PtRu) alloys highlighted, although the application of platinummolybdenum (PtMo) alloys for improved CO tolerance is discussed without drawing attention to the problems with CO2 tolerance (3); these negate any benefit. Durability, however, is not discussed and this is an important gap. The mechanisms of membrane failure that have limited adoption of the technology are not considered. Mechanical failure due to the stresses induced by dimensional change in the membrane, as it is hydrated then dehydrated during operation, and failure due to chemical attack from peroxide decomposition, are currently key areas of research and development (4). Nor has the important area of cell reversal due to fuel starvation, which can destroy a stack in minutes, been considered. The addition of water oxidation catalysts to the anode to mitigate against cell reversal is favoured by Johnson Matthey (3). Development of the much higher-temperature molten carbonate fuel cell (MCFC) and solid oxide fuel cell (SOFC) for large-scale MW grid applications is discussed in Chapters 8 and 9, respectively. The important technical disadvantages that have prevented adoption of the technologies are explained. For the MCFC the problems brought by the highly corrosive Li-K carbonate electrolyte in terms of electrode stability, electrolyte containment in the cell matrix and gas sealing of the stack are fully discussed. In the SOFC, the thermal mismatch between the ceramic cell and stack components that induces material cracking is highlighted, as is the desire to lower the operating temperature to minimise the problem and to reduce the cost of the balance of plant. The engineering student will find it illuminating to consider the ability of these fuel cells to use natural gas as a direct or indirect fuel, without the need to remove CO or CO2, and to consider the impact of the stack operating conditions on the performance through worked examples. Finally in Chapter 10 there is a very brief discussion of the direct methanol fuel cell (DMFC) operating in a PEMFC design, which is out of step with the increasing development of this technology for mobile telephone and leisure applications by a

number of companies. The key challenges of improved methanol oxidation kinetics and reduced methanol crossover are identified. It would have been appropriate, however, to discuss the large body of work on developing improved membranes and MEA designs for DMFCs, to reduce methanol crossover and MEA Pt loadings. Some comment on the expanding research on alternative fuels, such as direct ethanol and formic acid, might usefully have been added.

Conclusion While there are a few important areas that are not covered, and the text could have been smoothed to improve its comprehensibility, the book does succeed in the main aim of educating students (particularly in mechanical engineering) in the challenges presented by fuel cell technology. As the author advises in the preface, for fuel cell technology to succeed, a multidisciplinary approach from electrochemists, engineers and materials scientists is required. There is a growing need to educate and motivate the fuel cell engineers of the future.

References 1 2

3 4

D. Pletcher and F. C. Walsh, “Industrial Electrochemistry”, 2nd Edn., Chapman and Hall, London, 1990 “Handbook of Fuel Cells: Fundamentals, Technology, Applications”, eds. W. Vielstich, A. Lamm and H. A. Gasteiger, J. Wiley & Sons, Chichester, U.K., 2003, Vols. 1–4 T. R. Ralph and M. Hogarth, Platinum Metals Rev., 2002, 46, (3), 117 A. B. LaConti, M. Hamdan and R. C. McDonald, in “Handbook of Fuel Cells: Fundamentals, Technology, Applications”, eds. W. Vielstich, A. Lamm and H. A. Gasteiger, J. Wiley & Sons, Chichester, U.K., 2003, Vol. 3, Chapter 49, pp. 647–663

The Reviewer Professor Tom R. Ralph is Head of Electrochemical Engineering with Johnson Matthey Fuel Cells, Swindon, U.K. At Johnson Matthey he has been involved in the development of unit cells for PAFCs and MEAs for PEMFCs since 1989. During this time he has published widely, has generated over 20 patents, has run fuel cell courses at Strathclyde and Reading Universities, and has presented at a number of international conferences on the science and technology of fuel cells. He is presently visiting professor at the School of Engineering Sciences, University of Southampton and his main interests are in the engineering of materials for fuel cells, redox batteries and solar cells.

Platinum Metals Rev., 2006, 50, (4) 201

DOI: 10.1595/147106706X158374

10th Ulm Electrochemical Talks PGMS FEATURE IN RELIABILITY AND DURABILITY GAINS AND COST REDUCTION FOR ELECTROCHEMICAL ENERGY STORAGE AND CONVERSION Reviewed by Sarah C. Ball Johnson Matthey Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, U.K.; E-mail: [email protected]

The 10th Ulm Electrochemical Talks (UECT) were held from 27th to 28th June 2006 in NeuUlm, Germany. The Talks were organised by a number of Ulm-based organisations: the Zentrum für Sonnenergie- und Wasserstoff-Forschung (ZSW), DaimlerChrysler R&D Center, the University of Ulm and the University of Applied Sciences. Trends in the development of batteries, supercapacitors and fuel cells were discussed. Increasing consumer independence, requirements for emergency power and environmental concerns were cited as overall drivers for the development and commercialisation of these technologies. Batteries and supercapacitors are already commercially available for a wide range of applications, from hybrid vehicles to laptop computer and mobile telephone batteries. By contrast, fuel cell systems, on which this review primarily focuses, are still under development. However, advances in performance, lifetime and robustness were key themes, recurring throughout the meeting for all the various technologies discussed. Higher power densities and no need for recharging represent the significant advantages of fuel cell systems over batteries and supercapacitors, but wide-scale introduction of fuel cell technologies is currently limited by considerations of cost and durability, and the requirement for a hydrogen infrastructure or on-board hydrogen storage.

Proton Exchange Membrane Fuel Cells Mechanisms of component decay and accelerated tests were key features of the fuel cell sessions, as they were of the battery and supercapacitor sessions. T. Jarvi (UTC Power, U.S.A.) discussed the failure modes of the different fuel cell components within the membrane electrode assembly (MEA). Transient phenomena during start-up and shutdown accelerate degradation of the fuel cell


cathode where voltages up to 1.7 V RHE (reversible hydrogen electrode) may be encountered. UTC recommended a solution at the system level to mitigate this problem, as a materials solution requires an improvement of two to four orders of magnitude in corrosion resistance. This is not considered feasible using carbon support materials. UTC platinum-cobalt (PtCo) and platinum-iridiumcobalt (PtIrCo) alloy materials showed high stability in voltage cycling tests up to 1.15 V, with no leaching of Co observed. Peroxide attack is the critical cause of membrane decay. The hydrocarbon membrane biphenyl sulfone (BPSH) survived during open-circuit hold tests due to a low level of O2 permeation, although this material failed Fenton’s test, generally used for assessing membrane stability. Freeze-start capability and the importance of the robustness of seal materials, as well as of the MEA components, were also discussed. C. Stone (Ballard Power Systems, Canada) cited cost, durability, power density and freeze start capability as significant parameters for the commercialisation of proton exchange membrane fuel cell (PEMFC) stack technology, and outlined ‘road map’ objectives in terms of all these parameters to be achieved by 2010. Ballard Power Systems’ strategy aims to stimulate commercialisation by accelerating the development of emerging technologies such as higher-activity catalysts (enabling metal loading and hence cost to be reduced), hydrocarbon composite membranes, and low-cost gas diffusion layer materials. An ultimate cost target of U.S.$30 kW–1 was quoted, compared to the current U.S.$73 kW–1. However the attainment of this would also require improvement in balance of plant (BOP) and the removal of any requirement for external humidification. Achieving high performance using continuously coated MEA components and low-cost metal flow field plates is

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also essential for future scale-up plans. R. Ströbel presented results from DANA Corporation (Germany) and Zentrum für Sonnenergie- und Wasserstoff-Forschung (ZSW; Centre for Solar Energy and Hydrogen Research, Germany) on stamped metal bipolar plates for use in PEMFC applications. Use of metal plates improves the power density of PEMFC systems by reducing weight and volume. Costs are also reduced, and mass production is ultimately enabled. However, the sensitive nature of the MEA components requires that a highly corrosion-resistant, low-cost coating be found for the metal bipolar plates. The coating must also be compatible with and chemically resistant to the sealing materials used within the PEMFC stack. B. Bauer (FuMA-Tech, Germany) described the various membrane products available, including the ‘fumapem®’ series of membranes which include the fully fluorinated F-series, partially fluorinated P-series and other membranes with no fluorination. Strategies to reduce the overall cost of membrane materials were described, including low-cost ionomers, reinforcement to reduce thickness and retain strength, and the use of fillers or additives. However, cost reduction via the use of excessively thin membranes will compromise durability, and high performance rather than low cost was cited as the key requirement for membrane materials. The addition of inorganic films of silica, zirconium phosphide and carbon nanotubes in small concentrations have been used to reinforce the polymer reducing swelling and gas crossover and improving mechanical stability without affecting conductivity or flexibility of the membrane. Annealing of membranes doped within inorganic films enhanced their mechanical stability. S. Ball (Johnson Matthey, U.K.) described PtCo/C alloy materials with improved kinetic activity for the PEMFC cathode, and high stability during voltage cycling tests. Electronic and structural effects present in alloy particles enhance activity over that of Pt-only catalyst materials. Catalysts prepared on corrosion-resistant carbon supports of lower surface area showed improved resistance to corrosion at 1.2 V, as compared with that of commercially available carbon supports.


A. Khokhlov (Moscow State University and Russian Academy of Sciences, Russia) presented recent results on polybenzimidazole (PBI) membranes for operation from 150–200ºC. 4,4′-Diphenylphthalidecarbonic acid and 3,3′,4,4′tetraminodiphenyl ether derived PBI polymers are doped with 85% phosphoric acid, producing films holding 12–18 molecules of phosphoric acid per monomer unit. Protonic conductivity is retained up to 160ºC. Fuel cell testing at 175ºC showed around 5% performance loss using reformate containing 1.5% CO as the anode fuel. This is a significant enhancement in anode CO tolerance compared with that of MEAs operating at less than 100ºC. T. Schmidt (PEMEAs GmbH, Germany) also discussed PBI-based high-temperature MEAs, describing the enhanced tolerance of the Celtec®-P MEA to the CO, H2S and methanol in reformate mixtures, which is made possible by MEA operation at higher temperatures of 120–180ºC. The advantages of the system are simplification of the fuel processor, made possible by greater tolerance to impurities, no need for external humidification, and no membrane stability issues caused by peroxide. Major disadvantages of higher-temperature operation are the accelerated degradation of Pt/C catalysts, and redistribution of the H3PO4 electrolyte doped into the electrodes during operation, reducing catalyst utilisation and peformance. G. Scherer (Paul Sherrer Institute, Switzerland) reported how neutron radiography could be used to visualise the liquid water distribution in different components of a PEMFC in a segmented cell. By coupling the technique with in situ electrochemical impedance spectroscopy, changes in mass flow and current density may be correlated with humidification conditions. C. Hartnig (ZSW, Germany) also described the use of neutron radiography to image the liquid water within the serpentine flow field of a working fuel cell. The test can be performed without modifying or disturbing the fuel cell stack, producing a three-dimensional image of an operating cell. This can be correlated with current mapping and performance data to improve understanding of water transport processes within the PEMFC.

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Direct Alcohol Fuel Cells The challenges associated with direct alcohol fuel cells (DAFCs) were discussed by U. Stimming (Technische Universität München, Germany and Bayerischen Zentrum für Angewandte Energieforschung eV, Germany). Liquid fuels are particularly attractive for portable power applications due to their greater energy density than that of hydrogen. Much recent progress has been made using liquid-fed direct methanol fuel cells (DMFCs). An ultimate aim is to extend usage to other fuels such as ethanol, which can be produced by fermentation, or glycerol, which is available as a byproduct of fatty acid production. Oxidation of higher alcohols within low-temperature PEMFCs requires improved catalyst materials such as platinum-tin (PtSn), as the platinum-ruthenium (PtRu) materials currently used for methanol systems cannot fully oxidise ethanol, and become poisoned by organic fragments. DAFCs can operate using either acid or alkaline membranes, with the advantages of faster oxygen reduction kinetics and the capacity to use non-noble metal catalysts under alkaline conditions. Better electrolyte materials are required to reduce alcohol crossover, or highly selective catalysts are needed if cells are to be operated using a mixed alcohol/air feed. A PtRu black catalyst at the anode and a rutheniumselenium (RuSe) catalyst at the cathode were found to perform well in a mixed feed system. G. S. Park (Samsung Advanced Institute of Technology, Korea) reported on the long-term stability of DMFC systems where agglomeration and migration of Pt and Ru from the anode was observed during fuel cell testing. Accumulation of Ru at the cathode was observed to increase linearly with the MEA performance drop. However, both Pt and Ru migrated from the PtRu anode, so the Pt:Ru ratio observed at the anode did not change. Pt particles, up to 10 nm in size, were also observed within the membrane, along with evidence for membrane degradation from attack by radicals and peroxide.

Molten Carbonate Fuel Cells S. Rolf (MTU CFC Solutions GmbH, Germany) described the ‘HotModule’ stationary


carbonate fuel cell. This has the advantage of flexibility in fuel type: natural or biogas, methanol, coal gas or sewage/landfill gas are all possible fuels. High levels of CO2 – from 40–60% in some of these fuel types – were initially thought problematic; however, fuel cell voltage actually rose as CO2 was observed to migrate to the cathode side of the molten carbonate fuel cell (MCFC).

Poster Session Information presented within the poster session reflected the main themes of the Talks, covering high-temperature membranes, novel catalysts for oxygen reduction and alcohol oxidation, new Li-ion battery materials and the investigation of corrosion processes. The application of microscopy and spectroscopy techniques to PEMFC components and system modelling was also presented.

Conclusion New pgm-based alloy catalysts described at the conference showed enhancements in activity and stability over current Pt-only materials, and remain significantly more active than non-pgm catalysts. PtCo and PtIrCo alloys showed good activity and stability in voltage cycling tests representative of long term operation in automotive applications. PtSn and PtRu are key materials required for the operation of direct alcohol fuel cells (DAFCs), while RuSe catalysts have the benefit of alcohol tolerance and can be used as cathodes in DAFCs. The 10th UECT concluded with a farewell party at the Center for Solar Energy and Hydrogen at ZSW in Neu-Ulm. Historic Ulm was the birthplace of Albert Einstein, and the site of a tailor’s failed hang-glider launch across the Danube in 1811. The Minster has Europe’s tallest church tower, and according to legend, a famous sparrow helped with the logistics of construction. The Reviewer Sarah Ball is a Research Scientist in the Electrotechnology/Catalyst Preparation Group at the Johnson Matthey Technology Centre in the U.K. She is interested in anode catalysis for reformate-tolerant applications, and novel cathode materials and alloys for PEMFCs.

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SUSAN V. ASHTON

A TRIBUTE ON HER RETIREMENT AS EDITOR Platinum Metals to maintain and Review (PMR) has develop the high been fortunate over standard of contributhe fifty years of its tions from the existence in having a various research and very stable staff development estabestablishment. In lishments throughout particular, the prethe world of platsent Editor of PMR inum group metals is only the fourth to (pgms). This she did hold that title. The admirably. Susan was founding Editor, Dr well known for her Leslie Hunt, held the desire to maintain the position from 1956 highest possible qualuntil his death in ity for all the papers 1987. Dr Hunt’s successor, Ian Cottington, was published in PMR, and if this meant a long and Editor for seven years until his retirement in detailed exchange of correspondence with her 1994. The third Editor was Susan Ashton, who contributors to get things right to mutual satisheld the position from June 1994 until May faction, then that was what was done. Many 2006. authors, especially perhaps those whose first Susan joined Johnson Matthey as language was not English, will have greatly Patents/Information Assistant on PMR in appreciated the advice that Susan gave to help August 1977. She had them finalise their papers for publication. obtained a B.A. In addition to (Hons) in Physics content, Susan was from the University also most determined of Lancaster and an to make PMR appear M.Sc. in Information as attractive as possiScience from City ble, without comproUniversity, London. mising its long-estabPrior to joining lished reputation and Johnson Matthey she traditions. For 43 taught physics and years PMR was worked as Editorial issued with a characAssistant on Metals teristic plain cover. Abstracts for the Then, in 1999, Susan Metals Society. arranged for a comWhat were plete redesign of the Susan’s achievements (Left) The cover design used for Platinum Metals cover, giving the Review from its inception until 1999. (Right) The as Editor of PMR? redesigned cover introduced by Susan Ashton, and used journal a bright, Primarily they were until PMR became solely an E-journal modern scientific


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appearance that was in context with developments in the world of pgms. The appearance of the internal content was also enhanced with improved design, including new layout and fonts. In 2003, it was decided to publish PMR solely as an electronic journal. Susan herself would admit to having reservations about this move, feeling that it risked cutting off readers without access to a computer and the internet. But once these initial fears were resolved, she realised that a journal with its own internet site would provide many more opportunities for interaction with users, and instant access to any potential reader with an internet connection, thereby greatly extending the global readership

of the journal. The PMR website has achieved high ranking on internet search engines. www.platinummetalsreview.com provides a treasure trove of information: the journal itself, now augmented by the facility to search articles online; files in PDF format of past issues of the journal; a Question and Answer section; directories of people and organisations working with pgms; recommended reading lists; an events calendar; and links to a wide variety of relevant scientific and commercial information. Susan successfully brought PMR into the 21st century and can be proud of her legacy. We thank her for that, and wish her a long and happy M. C. F. STEEL retirement.

Pavla White Susan Ashton was ably supported during her Editorship by another longserving member of the PMR team, Pavla White. Born in Ostrava, Czech Republic, Pavla obtained a degree (Dipl.-Ing.) in Chemical Engineering from Vysoká Škola Bánská (Technical University) in Ostrava. She retired as the Senior Editorial Assistant on PMR in December 2005.

The Author Dr Mike Steel was Market Research & Planning Director of Johnson Matthey’s Precious Metal Products Division until his retirement in May 2006. He was in charge of the company’s precious-metals market research and publications, including Platinum Metals Review, the biannual market reviews Platinum and the internet portal Fuel Cell Today (www.fuelcelltoday.com). In addition, Dr Steel was responsible for Johnson Matthey’s Moscow office.


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ABSTRACTS of current literature on the platinum metals and their alloys PROPERTIES CHEMICAL COMPOUNDS Size Effects on the Thermal Conductivity of Polycrystalline Platinum Nanofilms

Growth and Characterization of Partially Oxidized Platinum Polymers in Nanoscale Templates

Q. G. ZHANG, B. Y. CAO, X. ZHANG, M. FUJII and K. TAKAHASHI,

B. M. ANDERSON, S. K. HURST, L. SPANGLER, E. H. ABBOTT, P. MARTELLARO, P. J. PINHERO and E. S. PETERSON, J. Mater. Sci.,

J. Phys.: Condens. Matter, 2006, 18, (34), 7937–7950

The thicknesses of the studied polycrystalline Pt nanofilms (1) ranged from 15.0–63.0 nm and the mean grain sizes varied from 9.5–26.4 nm. The thermal conductivities of (1) measured by a direct electrical heating method are greatly reduced from the bulk values, due mainly to grain-boundary scattering. Demixing of Solid-Soluted Co-Pd Binary Alloy Induced by Microwave Plasma Hydrogen Irradiation Technique T. TOKUNAGA, Y. HAYASHI, T. FUJITA, S. R. P. SILVA and G. A. J. AMARATUNGA, Jpn. J. Appl. Phys., Part 2, 2006, 45, (32),

L860–L863

Demixing in a solid-soluted Co-40 at.% Pd alloy was induced by microwave plasma H irradiation on a mixture of Pd-Co island grains on a Si substrate. Microstructure observation and X-ray microanalysis by TEM before and after the irradiation provided evidence of demixing in the metallic Co-Pd alloys. The possibility of the decomposition into Pd hydride and Co under irradiation at high temperatures is indicated. Surface Segregation and Homogenization of Pd70Ag30 Alloy Nanoparticles K.-W. WANG, S.-R. CHUNG and T.-P. PERNG, J. Alloys Compd., 2006, 422, (1–2), 223–226

In this study Pd70Ag30 nanoparticles (1) with the smallest size and the highest homogeneity were prepared using the strong reducing agent NaBH4. After heating (1), the surface segregation of Ag was small and the sintering was retarded by the high surface Pd concentration or by the residual B. There was significant surface segregation of Ag and sintering for (1) prepared by HCHO, where a higher concentration gradient existed inside (1). The behaviour of (1) prepared by N2H4 was intermediate between those of the other two samples.

2006, 41, (13), 4251–4258

The partially oxidised (PO) salts of the bis(oxalato)platinate(II) (1) and tetra(cyano)platinate(II) complexes were electrochemically prepared in glass capillary templates (900 nm in length), as well as through porous anodic Al oxide templates with pore diameters of 200 nm and 20 nm. The PO (1) polymers have significant flexibility on the nanoscale. The formation of the PO polymers could be directed by varying the positions and the number of electrodes. Multiple Additions of Palladium to C60 O. LOBODA, V. R. JENSEN and K. J. BØRVE, Fullerenes, Nanotubes,

Carbon Nanostruct., 2006, 14, (2–3), 365–371

DFT calculations on exohedral PdnC60 show that the Pd–fullerene bond energy remains essentially constant for n = 1–6. A Pd2(η2-C60) structure with the two metal atoms bridging over a six-membered ring is the most stable arrangement of two Pd atoms on the surface of C60. Entropy considerations suggest that isolated atoms and weakly bonded metal aggregates may exist in equilibrium. Binding of Pd atoms to the fullerene is preferred over Pd dimerisation. Fluorous Nanodroplets Structurally Confined in an Organopalladium Sphere S. SATO, J. IIDA, K. SUZUKI, M. KAWANO, T. OZEKI FUJITA, Science, 2006, 313, (5791), 1273–1276

and M.

Arrow-shaped N-donor ligands with perfluoroalkyl tails self-assembled with Pd ions in DMSO to form a shell in which the fluorinated chains (1) are directed inward toward the centre. Crystallographic analysis confirmed the rigid shell framework and amorphous interior. By varying the lengths of (1), the shell size could be tuned to encapsulate a liquid-like, disordered phase of ~ 2–6 perfluorooctane molecules.

Crystal Growth, Structure, Magnetic, and Transport Properties of TbRhIn5

Crystal Structure and Infrared Spectroscopy of Bis(2-hydrazinopyridine)palladium(II) Chloride and its Isotopomers

W. M. WILLIAMS, L. PHAM, S. MaQUILON, M. MOLDOVAN, Z. FISK, D. P. YOUNG and J. Y. CHAN, Inorg. Chem., 2006, 45, (12),

2006, 59, (5), 329–335

4637–4641

Single crystals of TbRhIn5 (1) were synthesised using the flux growth method. (1) is isostructural to CeRhIn5. The easy axis of magnetisation in (1) (TN = 47 K) is along the c axis. TN is enhanced by ~ 24% compared to that in TbIn3 (TN = 36 K). Although (1) is not a heavy fermion superconductor, it does have strong antiferromagnetic correlations.


P. DROZDZEWSKI, M. MUSIALA and M. KUBIAK, Aust. J. Chem.,

Reaction of PdCl2 with 2-hydrazinopyridine (hypy) in DMF gave [Pd(hypy)2]Cl2, whereas it recrystallised from MeOH to give [Pd(hypy)2]Cl2·2MeOH (1). Single crystal X-ray analysis of (1) revealed the planar structure of the metal vicinity and trans-orientation of the ligands, chelating the Pd through amine and pyridine N atoms. IR spectroscopy and DFT modelling were used to study the vibrations of [Pd(hypy)2]2+.

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Preparation of Five- and Six-Coordinate Aryl(hydrido) Iridium(III) Complexes from Benzene and Functionalized Arenes by C–H Activation

Electrochemical Capacitors Based on Electrodeposited Ruthenium Oxide on Nanofibre Substrates

H. WERNER, A. HÖHN, M. DZIALLAS and T. DIRNBERGER, Dalton Trans., 2006, (21), 2597–2606

Nanotechnology, 2006, 17, (12), 2865–2869

Reaction of the in situ generated cyclooctene Ir(I) derivative trans-[IrCl(C8H14)(PiPr3)2] with benzene at 80ºC gave a mixture of [IrH2(Cl)(PiPr3)2] and [IrH(C6H5)(Cl)(PiPr3)2] in the ratio of ~ 1:2. C6H5X (X = Cl, F), C6H4F2 and C6H4F(CH3) also reacted by C–H activation to afford [IrH(C6H4X)(Cl)(PiPr3)2], [IrH(C6H3F2)(Cl)(PiPr3)2] and [IrH{C6H3F(CH3)}(Cl)(PiPr3)2], respectively. The formation of isomeric mixtures was detected by 1H, 13C, 19F and 31P NMR spectroscopy. Oligo(U-terpyridines) and Their Ruthenium(II) Complexes: Synthesis and Structural Properties A. WINTER, J. HUMMEL and N. RISCH,

J. Org. Chem., 2006,

71, (13), 4862–4871

The domino reaction of tetrahydroquinolinone with bisiminium salts gave rigid U-shaped substituted terpyridines, bis(U-terpyridines) (L). Treatment of L with [(tpy)RuCl3] afforded [(tpy)Ru(L)Ru(tpy)]4+. A star-shaped tris(U-terpyridine) and [{(tpy)Ru}3(tris(Uterpyridine))]6+ were also obtained. The Ru complexes were light-emitting upon excitation at 340 nm, with broad emission maxima between 400–500 nm.

ELECTROCHEMISTRY Electrochemical Polymerization of Acetylene on Rh Electrodes Probed by Surface-Enhanced Raman Spectroscopy G.-K. LIU, B. REN, D.-Y. WU, J.-M. LIN, R.-A. GU and Z.-Q. TIAN,

J. Electroanal. Chem., 2006, 594, (2), 73–79

The electrochemical behaviours of C2H2 (1) on a roughened Rh electrode in 0.1 M HClO4 were studied by a combination of CV and SERS. On both roughened and smooth Rh surfaces, a clear loop in the cyclic voltammogram was present in the negative potential region. However, a surface species Raman signal was only observed for the roughened Rh surface. The resemblance of the detected signal to that of polyacetylene indicates the occurrence of polymerisation of (1) at potentials more negative than –0.3 V. Preparation and Characterization of RuO2–IrO2–SnO2 Ternary Mixtures for Advanced Electrochemical Technology and A. DE BATTISTI, Appl. Catal. B: Environ., 2006, 67, (1–2 ), 34–40

L. VAZQUEZ-GOMEZ, S. FERRO

The title coatings (1) were prepared by a thermal decomposition method, requiring an oxidative pyrolysis step of precursor salt deposits at 480ºC. The coating compositions were: IrxRu0.34–xSn0.66O2 (x nominal values = 1.7, 3.7, 7.3, 11.6, 17.9, 23.3, 28.4, 31.6 and 33.5%). (1) were deposited on Ti supports. A compromise between catalytic properties and wear resistance was found with coatings containing ~ 20% of Ir (hence ~ 15% of Ru).


Y. R. AHN, M. Y. SONG, S. M. JO, C. R. PARK

and D. Y. KIM,

Electrodeposition of RuO2 on electrospun TiO2 nanorods using CV increased the capacitance of RuO2. This is attributed to the large surface areas of the nanorods. The electrode deposited from 0.25– 1.45 V (with respect to Ag/AgCl) exhibited a specific capacitance of 534 F g–1 after deposition for 10 cycles with a scan rate of 50 mV s–1. The structural H2O content in RuO2 varied depending on the deposition potential range. Higher amounts of structural H2O in RuO2 increased the charge storage capability.

ELECTRODEPOSITION AND SURFACE COATINGS Catalyst-Enhanced Chemical Vapor Deposition of Palladium-Platinum Bilayer Films on Polyimide J. ZHENG, J. ZHOU, K. YU, X. GE and S. YU, Chin. J. Catal., 2006,

27, (6), 465–467

Catalyst-enhanced CVD of Pt, Pd and Pd-Pt bilayer films on polyimide using N2 and O2 as the carrier gases was studied at 220–300ºC under reduced or normal pressure. The films were deposited at a rate of 70–80 nm h–1. When a mixture of Pt complex and Pd complex was used as precursors in the same chamber, only Pt was deposited. Sequential deposition of Pd and Pt metals formed a Pd-Pt bilayer. Tarnishing Resistance of Silver–Palladium Thin Films M. DORIOT-WERLÉ, O. BANAKH, P.-A. GAY, J. MATTHEY and P.A. STEINMANN, Surf. Coat. Technol., 2006, 200, (24),

6696–6701

Thin Ag–Pd films (1) were deposited by magnetron cosputtering from Pd and Ag targets. Increasing Ar gas pressure and substrate temperature caused a drastic decrease of the specular reflectivity of (1). At constant deposition conditions the reflectivity of (1) decreased with increasing Pd content. Sulfidation test results indicated an improvement of tarnishing resistance of (1) with increasing Pd content.

APPARATUS AND TECHNIQUE Hydrogen Isotope Separation by Permeation through Palladium Membranes M. GLUGLA, I. R. CRISTESCU, I. CRISTESCU and D. DEMANGE,

J. Nucl. Mater., 2006, 355, (1–3), 47–53

Based on an experimentally verified mathematical model, a computational study was performed to show the net isotope effects in permeate and bleed flows when feeding a Pd permeator with H isotope mixtures under different feed and permeate pressures. The feasibility of H isotope permeation as a method for separation is discussed with regard to the process control for a single permeator or a cascade.

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Improved Photocatalytic Deposition of Palladium Membranes X. LI, Y. FAN, W. JIN, Y. HUANG and N. XU,

J. Membrane Sci.,

2006, 282, (1–2), 1–6

A TiO2 support was immersed into a photocatalytic deposition bath (PdCl2, HCl, EDTA, deionised H2O). Then the TiO2 membrane was lifted out, and subsequently a thin liquid film was formed on the TiO2 surface. The liquid film-coating was directly irradiated at room temperature. A tubular Pd membrane (0.4 μm thickness) was synthesised, which exhibited high H2 permeance of 4.8 × 10–6 mol m–2 s–1 Pa–1 and H2/N2 selectivity of 120 at 704 K.

HETEROGENEOUS CATALYSIS Naphthalene Oxidation over Vanadium-Modified Pt Catalysts Supported on γ-Al2O3 E. N. NDIFOR, T. GARCIA and S. H. TAYLOR, Catal. Lett., 2006,

110, (1–2), 125–128

Effect of Carbon Nanotubes on Activity of Rh-CeMn/SiO2 Catalyst for CO Hydrogenation to Oxygenates L. HUANG, W. CHU, J. HONG and S. LUO, Chin. J. Catal., 2006,

27, (7), 596–600

The catalytic performance of C nanotubes (CNTs)promoted Rh-Ce-Mn/SiO2 (1) for CO hydrogenation to oxygenates was studied. The CNTs improved the dispersion of Rh and increased the active components on the surface of (1). The amount of strongly adsorbed H2 or CO on the surface of (1) was increased. The results of CO hydrogenation showed that the CNTs enhanced the activity of (1). Ruthenium Hydroxide on Magnetite as a Magnetically Separable Heterogeneous Catalyst for Liquid-Phase Oxidation and Reduction M. KOTANI, T. KOIKE, K. YAMAGUCHI and N. MIZUNO,

Green

Chem., 2006, 8, (8), 735–741

Pt/γ-Al2O3 catalysts (1) modified by V were prepared and then tested for the complete oxidation of naphthalene. Only 0.5% V promoted the activity of 0.5% Pt/γ-Al2O3. The enhancement is related to the presence of a more easily reducible V species coupled with the enhanced number of surface Pt sites. The reduced activity of (1) with higher V content (1–12%) is attributed to the presence of crystalline V2O5.

Ru(OH)x/Fe3O4 (1) can be used as the catalyst for: (a) aerobic oxidation of alcohols; (b) aerobic oxidation of amines; and (c) reduction of carbonyl compounds to alcohols using 2-propanol as a H donor. Separation of (1) from the product(s) was easily achieved with a permanent magnet, and > 99% of (1) could be recovered for each reaction. (1) recovered after these reactions could be reused.

Pd and Pt Catalysts Supported on Carbon-Coated Monoliths for Low-Temperature Combustion of Xylenes

HOMOGENEOUS CATALYSIS

A. F. PÉREZ-CADENAS, F. KAPTEIJN, J. A. MOULIJN, F. J. MALDONADO-HÓDAR, F. CARRASCO-MARÍN and C. MORENOCASTILLA, Carbon, 2006, 44, (12), 2463–2468

C-coated monoliths (1) were prepared from polyfurfuryl alcohol coated cordierite structures. Pd and Pt catalysts were obtained by equilibrium impregnation of (1). The catalysts were pretreated in H2 at 300ºC. The Pt catalysts were more active in xylene combustion. Complete combustion was reached at 150–180ºC with a total selectivity to CO2 and H2O. Combustion of m-xylene was easier than p-xylene. A Selective Synthesis of Acetic Acid from Syngas over a Novel Rh Nanoparticles/Nanosized SiO2 Catalysts W.-M. CHEN, Y.-J. DING, D.-H. JIANG, T. WANG and H.-Y. LUO,

Catal. Commun., 2006, 7, (8), 559–562

Microemulsions of polyethyleneglycol-p-nonylphenyl ether in cyclohexane were prepared by injecting aqueous RhCl3 solutions. Rh–N2H4 nanoparticles (1) were formed by addition of hydrazine hydrate. (1) were separated from the oil phase. After the supernatant was decanted, (1) were washed, dried and calcined. Rh nanoparticles/nanosized SiO2 (2) was prepared by grinding the resultant Rh nanoparticles with nanosized SiO2. The total selectivity of acetic acid and ethyl acetate in the oxygenate products of CO hydrogenation on (2) reached 74.8%.


A User-Friendly, All-Purpose Pd-NHC (NHC = NHeterocyclic Carbene) Precatalyst for the Negishi Reaction: A Step Towards a Universal CrossCoupling Catalyst M. G. ORGAN, S. AVOLA, I. DUBOVYK, N. HADEI, E. A. B. KANTCHEV, C. J. O’BRIEN and C. VALENTE, Chem. Eur. J., 2006,

12, (18), 4749–4755

The air stable, highly active, precatalyst PEPPSI-IPr (PEPPSI = pyridine-enhanced precatalyst preparation, stabilisation and initiation; IPr = diisopropylphenylimidazolium derivative) can be used with PdCl2 for the Negishi reaction. Organohalides and routinely used pseudohalides were excellent coupling partners. General laboratory techniques are employed for all of the reactions. Open-Vessel Microwave-Promoted Suzuki Reactions Using Low Levels of Palladium Catalyst: Optimization and Scale-Up N. E. LEADBEATER, V. A. WILLIAMS, T. M. BARNARD and M. J. COLLINS, Org. Process Res. Dev., 2006, 10, (4), 833–837

Suzuki couplings using low Pd catalyst concentrations (1–5 ppm Pd) with microwave heating have been transferred from sealed-vessel to open-vessel reaction conditions. The procedure is scalable from the mmol to the 1 mol scale. The reactions can be performed in air and are run using H2O/EtOH as the solvent system. The couplings are complete within 20 min of heating at reflux.

209

Highly Enantioselective Fluorination Reactions of β-Ketoesters and β-Ketophosphonates Catalyzed by Chiral Palladium Complexes Y. HAMASHIMA, T. SUZUKI, H. TAKANO, Y. SHIMURA, Y. TSUCHIYA, K. MORIYA, T. GOTO and M. SODEOKA, Tetrahedron,

2006, 62, (30), 7168–7179

Using chiral Pd enolates as key intermediates, highly enantioselective fluorination reactions (≤ 98% ee) of β-ketoesters and β-ketophosphonates have been carried out. These reactions were carried out in alcoholic solvents without any need to exclude air and H2O. Transformation of the fluorinated products was successfully achieved. Nitrogen Ligand-Containing Rh Catalysts for the Polymerization of Substituted Acetylenes I. SAEED, M. SHIOTSUKI and T. MASUDA, J. Mol. Catal. A: Chem., 2006, 254, (1–2), 124–130

Rh complexes having a phenoxy-imine ligand, a βdiiminate ligand, and NH3 ligands were used in the polymerisation of substituted acetylenes. Polymers in moderate to high yields with high molecular weights were afforded. A cocatalyst was not required in these systems in contrast to [Rh(nbd)Cl]2 and [Rh(cod)Cl]2. In the case of the phenoxy-imine catalysts, the nbdbearing one was more active than the cod-bearing counterpart, while the opposite trend was observed for the β-diiminate catalysts. The Hydrogenation of Cinnamaldehyde by Supported Aqueous Phase (SAP) Catalyst of RhCl(TPPTS)3: Selectivity, Kinetic and Mass Transfer Aspects

K. NUITHITIKUL and J. M. WINTERBOTTOM, Chem. Eng. Sci., 2006, 61, (18), 5944–5953

The hydrogenation of trans-cinnamaldehyde was catalysed by RhCl(TPPTS)3/SiO2 (1) (TPPTS = trisodium salt of tris(m-sulfophenyl)phosphine). The hydrogenation is selective at the C=C bonds in cinnamaldehyde giving hydrocinnamaldehyde as the main product. High selectivity (99.9%) was achieved by employing a low initial concentration of cinnamaldehyde. Optimum H2O content of (1) giving maximum activity occurred when the pore volume of the supports was completely filled with H2O. Isomerizing-Hydroboration of the Monounsaturated Fatty Acid Ester Methyl Oleate K. Y. GHEBREYESSUS and R. J. ANGELICI, Organometallics, 2006,

25, (12), 3040–3044

[Ir(cyclooctene)2Cl]2/dppe catalysed the hydroboration of methyl oleate (18:1) with pinacolborane to give a product (1) in which the boronate ester group is in the terminal (C18) position. The formation of (1) shows that the catalyst promotes both the isomerisation of the double bond from the 9,10-position of 18:1 to the terminal position and the selective hydroboration of this isomer to give (1) in 45% yield. This tandem reaction is claimed to have the potential to be capable of converting all isomers of 18:1 into (1).


FUEL CELLS Preparation of High Catalyst Utilization Electrodes for Polymer Electrolyte Fuel Cells J. M. SONG, S. SUZUKI, H. UCHIDA and M. WATANABE, Langmuir,

2006, 22, (14), 6422–6428

Pt/C black (high surface area) and Nafion ionomer solution were heated in an autoclave at 200ºC, followed by quenching to form an ink (1). A cathode prepared with (1) exhibited high catalyst utilisation and improved gas diffusivity. The autoclave treatment promoted an effective introduction of Nafion ionomer into primary pores of the Pt/C black agglomerates. Characteristics of a Platinum Black Catalyst Layer with Regard to Platinum Dissolution Phenomena in a Membrane Electrode Assembly K. YASUDA, A. TANIGUCHI, T. AKITA, T. IOROI and Z. SIROMA, J. Electrochem. Soc., 2006, 153, (8), A1599–A1603

Pt dissolution and precipitation in a PEM of a MEA was studied using a potential holding experiment at 1.0 V vs. a reversible H electrode and HRTEM. The electrochemically active surface area decreased depending on the holding time, and Pt deposition was observed in the PEM near a cathode catalyst layer. However, Pt dissolution and deposition out of the catalyst layer were greatly reduced when a Pt black electrode was employed. Using a double-layered catalyst layer, Pt redeposited on the Pt black surface. Characterization of Membrane Electrode Assembly for Fuel Cells Prepared by Electrostatic Spray Deposition M. UMEDA, S. KAWAGUCHI and I. UCHIDA, Jpn. J. Appl. Phys., Part 1, 2006, 45, (7), 6049–6054

A Pt/C MEA prepared by electrostatic spray deposition was installed in a fuel cell and demonstrated as high a performance as that of a MEA prepared by airspraying. The cross-sectional morphology of the catalyst layer explained the coupling strength in a peel-off test and the dependence of current-voltage characteristics on catalyst layer thickness. Synthesis, Characterization, and Electrocatalytic Activity of PtBi and PtPb Nanoparticles Prepared by Borohydride Reduction in Methanol C. ROYCHOWDHURY, F. MATSUMOTO, V. B. ZELDOVICH, S. C. WARREN, P. F. MUTOLO, M. BALLESTEROS, U. WIESNER, H. D. ABRUÑA and F. J. Di SALVO, Chem. Mater., 2006, 18, (14),

3365–3372

PtPb and PtBi nanoparticles displayed enhanced electrochemical activity toward formic acid and MeOH oxidation as compared with those of Pt and PtRu nanoparticles. The electrocatalytic activity of the PtPb nanoparticles was studied as a function of sonication time of the catalyst ink, and morphology changes were followed by SEM. The activity of the PtPb catalyst initially increased with sonication time, peaked at 6 h, and then decreased.

210

DOI: 10.1595/147106706X154602

NEW PATENTS METALS AND ALLOYS

Rhodium-Containing Catalysts

Palladium-Containing Silver Alloy KYOCERA CORP

Japanese Appl. 2006-037,183

A Pd-containing Ag alloy (1), having a blackish colour and a metallic lustre, with good resistance to sulfur is claimed. (1) contains (in wt.%): 10–40 Sn, 1–10 Pd and ≥ 50 Ag. Further, if necessary, either one or both of (in wt.%): 1–5 Co and 1–5 In, may be added. (1) may be used for ornamental objects.

ELECTRODEPOSITION AND SURFACE COATINGS Fabrication of a Rocket Engine Chamber AEROJET-GEN. CORP

U.S. Appl. 2006/0,124,469

CELANESE INT. CORP

European Appl. 1,694,435

A method of producing a catalyst or precatalyst for making alkenyl alkanoates includes four aspects which may be applied separately or in combination. The first aspect includes a Pd/Au catalyst or precatalyst with Rh on a support material (1), which may optionally be calcined. The second aspect is that (1) may be layered, with one layer free of catalytic components; the third aspect is that (1) may contain zirconia; the fourth aspect is that the catalytic components may be substantially Cl-free. 1,2-Diamino-3-methylcyclohexane Production BASF AG

World Appl. 2006/066,762

A method for manufacturing a rocket engine combustion chamber uses electrodeposition to form a uniform layer of Ir on a mandrel. A controlled atmosphere plasma spray (CAPS) process is then used to deposit a structural refractory layer such as metals or alloys of Re, Mo, W, Ta, or a mixture, onto the Ir layer. A second CAPS process applies a transition refractory layer containing Nb or Ta.

A method for producing 1,2-diamino-3-methylcyclohexane and/or 1,2-diamino-4-methylcyclohexane is disclosed. 2,3- and/or 3,4-diaminotoluene is reacted with H2 under high pressure (100–300 bar) and high temperature (130–220ºC), in the presence of a Rh/γ-alumina catalyst containing 1–25 wt.% Rh relative to substrate. A dialkyl ether and/or an alicyclic ether is used as the solvent, with 5–500 mol% NH3 added relative to substrate.

APPARATUS AND TECHNIQUE

Preparation of Palladium Biocatalysts

Neutron Detector Assembly with Rhodium Emitters

CNRS

A. Y. C. CHENG

U.S. Appl. 2006/0,165,209

A system to measure neutron flux in a nuclear fuel assembly includes at least two detectors of differing length, made from Rh. Each detector has an outer sheath forming an inner volume into which an inner emitter is placed, which is structured to accept neutrons and provide an electrical signal. The signal is transmitted to an exterior lead by at least one lead connected to each emitter. Material for Air Bag Inflator Primer TANAKA KIKINZOKU KOGYO KK


World Appl. 2006/087,334

A bacterium strain (1) having a gene coding for a membrane-bound [NiFe] hydrogenase (2), or membrane extracts (3) containing (2) are used for the preparation of metallic biocatalysts containing Pd, Pt, Ru, Rh or Ir. For example, a solution of Pd(II) is brought into contact with (1) or (3) to allow initial sorption of Pd(II), then H2 gas is bubbled through to precipitate Pd in reduced form. The resulting Pd(0) particles are cheaper to produce, have smaller particle size and higher catalytic activity than other methods. Electrochemical Palladium Catalysed Reaction COMBIMATRIX CORP

U.S. Appl. 2006/0,151,335

A Pd alloy (1) for an air bag inflator primer having high specific resistance value, good workability, and excellent corrosion resistance is claimed. (1) contains 5–30 wt.% Mo and the balance Pd. (1) is used as a fuse for an air bag inflator and can be manufactured at low cost, compared with alternative materials.

An isolated Pd(0) catalysed reaction, preferably a Heck reaction, is performed on an electrode array device. The electrodes are immersed in a solution of a transition metal catalyst system containing Pt or Pd, plus a confining agent such as an oxidant to convert Pd(0) to Pd(II), to limit diffusion of catalyst. Catalyst is regenerated by biasing one or more electrodes.

HETEROGENEOUS CATALYSIS

Spongy Platinum Nanoparticles

Water Gas Shift Reactor

UNIV. MIYAZAKI

JOHNSON MATTHEY PLC

British Appl. 2,423,489

A water gas shift reactor is claimed which includes two different catalyst zones arranged in close proximity. The temperature of the gases leaving the first zone is the same as that of the gases entering the second. The first zone catalyst has positive-order kinetics and consists of Au dispersed on ceria or zirconia, and the second zone catalyst has negative-order kinetics and consists of Pt dispersed on ceria or zirconia.



Spongy nanoparticles (1) containing Pt are fabricated by reducing a chloroplatinic acid salt with a borohydride salt, in the presence of two ionic or nonionic surfactants. (1) have a porous single crystal structure with outer diameter 20–100 nm, with rodlike frames of diameter 1.5–4 nm interconnected in 3 dimensions, to give fine pores of size 0.3–2 nm. (1) can be used as catalysts for fuel cells or exhaust gas treatment, and in electrodes or sensors.

211

HOMOGENEOUS CATALYSIS 2-Substituted Propionic Acids and Amides British Appl. 2,422,603

PHOENIX CHEM.

A process for preparation of 2-substituted propionic acids and amides includes converting a substrate by enantioselective hydrogenation. Preferred hydrogenation catalysts include a ligand containing a metallocene group with a chiral P or As substituent, a linker group such as a ferrocene or a diphenyl ether, and a metal chelating group. A metal such as Rh, Ru, Ir, Pd, Pt or Ni is coordinated to the ligand.

Palladium-Cobalt Particles as Electrocatalysts World Appl. 2006/086,457

Pd/Co particles (1) are used in O2-reducing cathodes for fuel cells. (1) may be in the form of nanoparticles of diameter between ~ 3–10 nm and may be supported on C black, graphitised C, graphite or activated C. (1) may have a binary alloy composition represented by the formula Pd1–xCox, where x is between ~ 0.1–0.9. Anode Electrode NITTO DENKO CORP

NIPPON STEEL CORP


A bulk oxide superconductor, high in critical current density, consists of particles of BaCeO3 or Ba(Ce1–aMa)O3–b (0 < a < 0.5 and 0 ≤ b ≤ 0.5, M is a metal such as Zr, Hf, Sn) dispersed as pinning centres in a crystal of RE1+xBa2-xCu3Oy (0 ≤ x ≤ 0.1 and 6.5 ≤ y ≤ 7.2, RE is at least one element selected from the group consisting of Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Yb). One or both of Pt and Rh are added, between 0.1–5 wt.% of the material.

MEDICAL USES

FUEL CELLS BROOKHAVEN SCI. ASSOC.

Superconducting Oxide Material


An anode and a membrane-electrode junction are claimed which can reduce the cost of a solid polymer fuel cell, by improving the output of a Pt catalyst used for the anode. The catalyst layer includes Pt and a proton conductive polymer carried on a porous base. Particles of diameter < 100 nm, selected from Si oxide, Ti oxide or Al oxide are also included.

ELECTRICAL AND ELECTRONIC ENGINEERING Platinum(II) Complexes in OLEDs European Appl. 1,692,244

Antitumour Compositions with Platinum Derivatives SCHERING CORP

World Appl. 2006/057,998

Combination compositions including a Pt-based compound, such as satraplatin, along with another chemotherapeutic agent such as temozolomide or lonafarnib are claimed. The combinations can be used for the prevention or treatment of various cancers in human patients. The pharmaceutical composition can be formulated into a single oral dosage form with a pharmaceutically acceptable carrier or administered as separate components. Noble Metal Dental Alloy P. J. CASCONE

U.S. Appl. 2006/0,147,334

A dental alloy containing Ru which can be cast or machined into a dental prosthesis consists of > 25% metal selected from Ru, Pt, Pd, Ir, Os and Au, with > 15% or the greater portion being Ru, plus 15–30% Cr. The balance consists of a metal chosen from Fe, Ni and Co. Optionally, other elements can be added (in %): ≤ 15 Ga, ≤ 5 Si, ≤ 1 B; and/or ≤ 5 Nb, Ta or Re. New Gene Expression Inhibitor SCI. UNIV. TOKYO


Pt(II) complexes (1) are used as emitter molecules in OLEDs. (1) may include phosphine, bathophen or bipyridyl ligands, which may contain CN, acetylide, thiocyanate or isocyanate groups plus aryl, alkyl, heteroaryl or alkenyl groups. The OLEDs can be used in various devices including static screens for computers and televisions, or in screens for mobile devices such as mobile phones, laptops and vehicles.

A new Pt-containing compound (1) capable of inhibiting gene expression based on a specific sequence is described. The structure of (1) includes two 5- or 6-membered rings each containing at least one N atom, with one N atom in each ring binding to Pt. The rings may be pyridine, pyrazine, pyrimidine, triazine, thiazole or imidazole rings. (1) is combined with a nucleic acid sequence related to a specific gene to achieve gene expression inhibition.

Recording Medium and Reproducing Method

High Frequency Treatment Tool for Endoscope

BASF AG

KYOTO UNIV.


A high density recording medium (1) for digital holograms contains a recording layer consisting of a thin film of nanoparticles (2) containing Pt, Pd or Ni, with average particle size and film thickness of 3–20 nm. (1) uses laser light from near-UV to visible wavelengths to give instant recording and good stability. Information is recorded as a pattern of interference fringes between aggregated and non-aggregated regions of (2), induced by two beams of laser light: an information beam and a reference beam.


PENTAX CORP


A high-frequency treatment tool consists of a stainless steel or W alloy electrode (1), partly or completely coated with Pt or Au metal or their alloys, by plating, vacuum evaporation or ion plating. (1) is arranged at the distal end of an electrically insulated sheath inserted into the treatment tool insertion channel of an endoscope. (1) can be used to cauterise living tissue, without causing viable tissue to stick to it even under conditions of high-frequency treatment, and can be used continuously and repeatedly at high frequency.

212

NAME INDEX TO VOLUME 50 Page

Abbott, E. H. 207 Abruña, H. D. 210 Adams, R. D. 152 Ager, D. J. 54 Ahn, Y. R. 208 Akita, T. 210 Alapieti, T. 13 Alexeev, O. S. 152 Amaratunga, G. A. J. 207 Amiridis, M. D. 152 Anandan, S. 47 Anderson, B. M. 207 Anderson, J. A. 20 Angelici, R. J. 210 Apanel, G. 40 Arblaster, J. W. 97, 118 Arm, K. J. 104 Arteaga, G. 195 Ashfield, L. 95 Ashton, S. V. 205 Athawale, A. A. 152 Aubuchon, S. R. 153 Avola, S. 209 Azambuja, V. M. 150 Baboo, R. 106 Bahnemann, D. 24 Bailey, G. C. 36 Bailie, J. 177 Balaban, A. T. 36 Baldwin, E. 105 Ball, S. C. 202, 203 Ballarin, B. 105 Ballesteros, M. 210 Banakh, O. 208 Banks, C. E. 105 Banks, R. L. 36 Bard, A. J. 105 Barnard, T. M. 209 Basini, L. 64 Basset, J. M. 36 Batchelor-McAuley, C. 105 Baturina, O. A. 153 Bauer, B. 203 Beamson, G. 46 Bellussi, G. 23 Bencze, L. 36

Page

Bercaw, J. 171 Bernhard, S. 47 Betancourt, P. 48 Bhagwat, S. V. 152 Birss, V. I. 153 Boardman, A. 67 Boelhouwer, C. 36 Bogart, K. H. A. 153 Bolton, C. 42 Børve, K. J. 207 Bottini, S. 152 Bowker, M. J. 24, 179 Boyko, V. 104 Braucks, R. S. 177 Britovsek, G. J. P. 150 Bronstein, L. 25 Brown, R. 196 Browning, D. 43 Bruneau, C. 95 Bruno, C. 105 Bruss, A. J. 153 Buchmeister, M. R. 36 Buchwald, S. L. 106 Burch, R. 24, 178 Cabeza, G. F. 151 Cagran, C. 144 Cai, P. 48 Calderon, N. 36 Cameron, D. S. 38 Cao, B. Y. 207 Cao, Y. 47 Captain, B. 152 Carano, M. 105 Carrasco-Marín, F. 209 Casci, J. L. 23 Caseri, W. 112 Castellani, N. J. 151 Cawthorn, R. G. 13, 130 Centi, G. 22 Chan, J. Y. 207 Chaplin, B. P. 152 Chatani, N. 95 Chatterjee, D. 2 Chatterjee, U. K. 47, 104 Chauvin, Y. 35 Chen, C.-C. 105 Chen, C. Y. 107 Chen, J. 48


Page

Chen, R. Chen, W.-M. Chen, Y.-W. Chianese, A. Chisholm, J. D. Chiuzbaian, S. G. Choudhury, B. Chu, W. Chung, S.-R. Ciardelli, C. Cimino, S. Cipriano, G. Cohen-Karni, I. Coldea, M. Collins, M. J. Compton, R. G. Cottington, I. Courtois, X. Crabtree, R. H. Cristescu, I. Cristescu, I. R. Cristiani, C. Crofton, J. Crowhurst, J. C. Crowson, P.

48 209 105 171 106 150 151 209 207 178 64 42 46 150 209 105 205 178 171 208 208 106 153 104 42

Damiani, D. E. Danheiser, R. L. Danylyuk, O. De Battisti, A. de Vries, A. H. M. de Vries, J. G. De, G. S. Delmas, M. Demange, D. Demonceau, A. Demoulin, O. Deubel, D. V. Devi, R. N. Diels, G. Ding, Y.-J. Dirnberger, T. DiSalvo, F. J. Dixneuf, P. H. Dolgoplosk, B. A. Doriot-Werlé, M. Dos Santos, D. S. Dragutan, I. Dragutan, V.

152 48 104 208 54 54 2 47 208 36 65, 66 107 24 49 209 208 210 36, 95 36 208 150 36, 81 36, 81

Page

Drozdzewski, P. 207 Du, Y. W. 46 Du, Z. 104 Duan, C.-G. 153 Dubovyk, I. 209 Dunleavy, J. K. 52, 110, 156 Dupont, J. 153 Dziallas, M. 208 Echegoyen, L. Eleuterio, H. S. Emrick, T. Ernst, W. Evans, C. L.

150 36 49 39 104

Fagalde, F. 151 Fan, Y. 209 Feast, J. M. 36 Fernández, M. B. 152 Fernandez-Ruiz, P. 44 Ferreira, F. C. 153 Ferreira, J. L. 104 Ferreira, P. J. 49 Ferro, S. 208 Fierro, J. L. G. 152 Finkel’stein, E. 36 Fischer, B. 158 Fischer, N. O. 49 Fischmeister, C. 95 Fisk, Z. 207 Fontana, J. 134 Fontana, M. 112 Frey, G. D. 104, 150 Fruchart, D. 150 Fu, Q. J. 21 Fübi, M. 39 Fujii, M. 207 Fujita, M. 207 Fujita, T. 48, 207 Fürstner, A. 36 Furukawa, K. 49 Furuta, H. 150 Gagné, M. Galanski, M. Gale, P. A. Garcia, T. García, M. F.

171 49 47 209 20

213

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Gasteiger, H. A. 49 Gates, B. 194 Gay, P.-A. 208 Gayatri 106 Ge, X. 208 Gelesky, M. A. 153 Gelin, P. 65 Ghaleb, R. A. 65 Ghebreyessus, K. Y. 210 Giani, L. 106 Girishkumar, G. 107 Glugla, M. 208 Göbel, U. 178 Goldsmith, J. I. 47 Golunski, S. E. 194 Goncharov, A. F. 104 Goto, T. 210 Gottesfeld, S. 41 Gray, P. 41 Greig, D. 46 Grela, K. 106 Griffith, W. P. 77 Groppi, G. 106 Groszek, A. J. 46 Grubbs, R. H. 35, 95 Grunwaldt, J.-D. 178 Gu, R.-A. 208 Gulajski, L. 106 Guldi, D. M. 150 Gummert, G. 44 Guo, C. 104 Guo, F. 151 Guy, K. A. 152 Gwak, J. 152 Haber, J. 46 Hadei, N. 209 Hamashima, Y. 210 Hanks, J. 151 Hargreaves, J. 195 Hartinger, C. G. 49 Hartnig, C. 203 Hatchett, D. W. 151 Hayashi, Y. 207 Heinen, J. 43 Helminen, J. 106 Henry, C. R. 24, 26 Herdtweck, E. 150 Hérisson, J.-L. 35 Herrmann, W. A. 36, 104, 150

Page

Hester, H. R. 151 Heymann, G. 46 Hinde, P. 177 Hine, P. J. 46 Hirano, M. 96 Hocker, H. 36 Hoffmann, R.-D. 46 Höhn, A. 208 Holmes, A. B. 48 Holmes, K.-A. 153 Hong, J. 209 Hong, R. 49 Hostyn, S. 49 Hotanen, U. 106 Hou, Q. 47 Houel, V. 177 Hrapovic, S. 47 Huang, L. 209 Huang, Y. 209 Huang, Y.-S. 151 Hugh, M. 119 Hummel, J. 208 Hummel, K. 36 Hungria, A. B. 152 Hunt, L. 205 Huppertz, H. 46 Hurst, S. K. 207 Hutchings, G. 22, 194 Igarashi, A. Iida, H. Iida, J. Ikariya, T. Ikehara, T. Ikeno, T. Iljana, M. Ilkenhans, T. Imamoglu, Y. Inoue, A. Ioroi, T. Ishihara, A. Isikawa, Y. Isnard, O. Itoh, K. Ivin, K. J. Iwasawa, Y. Jackson, K. M. Jackson, S. D. Jacobs, P. Janssen, G. J. M.


152 152 207 107 152 150 13 22 36 46 210 107 150 150 95 36 48 15 24 23 49

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Janssens, T. Jarvi, T. Jaswal, S. S. Jaworska, M. Jazzar, R. F. R. Jensen, V. R. Jia, L. Jiang, D.-H. Jiang, N. Jiang, S. P. Jin, W. Jin, Z.-L. Jo, S. M. Johnson, A. Johnston, P. Johrendt, D. Joliot-Curie, F. Joliot-Curie, I. Jones, T. Jones, T. G. J. Jurczakowski, R.

194 202 153 47 95 207 105 209 106 49 209 153 208 42 20 46 98 98 67 105 104

Kadish, K. M. Kajihara, M. Kakiuchi, F. Kalantari, D. J. Kalchenko, V. Kamat, P. Kamiya, N. Kantchev, E. A. B. Kapteijn, F. Katre, P. P. Katz, N. E. Katz, T. J. Kawaguchi, S. Kawaguchi, Y. Kawamara, M. Kawano, M. Keppler, B. K. Khair, M. Khinast, J. G. Khokhlov, A. Khosravi, E. Kiely, C. Kihn, Y. Kilcoyne, S. H. Kilday, P. Kim, D. Y. Kim, H.-I. Kim, Y.-G. King, A. E.

150 46 95 105 104 107 107 209 209 152 151 36 210 39 44 207 49 177 48 203 36 196 47 46 196 208 49 151 153

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King, D. Kinyanjui, J. M. Kitamura, M. Kitano, M. Klak, J. Klotsman, S. M. Ko, F.-H. Kocha, S. Koike, T. Koltsakis, G. Komiya, N. Konagawa, J. Kondo, K. Kondo, T. Kongkanand, A. Kopperud, T. Korotcov, A. Kosarev, V. F. Kotani, M. Kotobuki, M. Koyima, S. Krummrich, S. Kruszynski, R. Kubiak, M. Kündig, E. P. Kurokawa, N. Kuwabata, S. Kuwai, T. Kwok, T. J. Kwon, H. J. Kwon, Y. H.

38 151 95 24 47 29 105 49 209 178 95 150 152 95 107 103 151 22 209 48 96 42 47 207 95 46 107 150 48 179 49

la O’, G. J. 49 La Parola, V. 152 Lalik, E. 46 Lambert, R. 26, 196 Lampeka, Y. 104 Lang, C. 15 Lasia, A. 104 Latha, S. 47 Law, D. J. 150 Leadbeater, N. E. 209 Lebedeva, N. P. 49 Lee, J. W. 105 Lee, K. 107 Légaré, P. 151 Lemaire, J. 177 Lennon, D. 195 104 Leslie, W. Li, F. 47 Li, Q. 46

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Li, W. 152 Li, X. 171, 200, 209 Liao, S. 153 Light, M. E. 47 Lightner, V. 44 Lin, H.-Y. 105 Lin, J.-M. 208 Lin, M. 105 Lipkowski, J. 104 Liu, C. 107 Liu, G.-K. 208 Liu, T.-F. 105 Liu, Y. 47 Liu, Z. 49 Livingston, A. G. 153 Lloyd, A. 38 Loboda, O. 207 Loones, K. T. J. 49 Louzguine-Luzgin, D. V. 46 Lowry, M. S. 47 Lu, M. 46 Lu, Q. 150 Luo, H.-Y. 209 Luo, S. 209 Luo, Z. 49 Luong, J. H. T. 47 Lupton, D. F. 158 Lux, K. W. 107

Mauger, C. 106 Meelich, K. 49 Mei, W.-N. 153 Melada, S. 22 Mellace, M. G. 151 Melo, L. 48 Merker, J. 158 Michrowska, A. 106 Midgley, P. A. 152 Mignani, G. 106 Mino, T. 48 Mitra, A. 2 Mitsudo, T. 95 Mitsushima, S. 107 Miura, S. 69 Mizuno, N. 209 Mizushima, T. 150 Mohri, T. 69 Mol, J. C. 36 Moldovan, M. 207 Monari, M. 105 Mondal, K. 47, 104 Morales, M. 150 More, K. 105 Moreno-Castilla, C. 209 Morgan, D. 49 Moriya, K. 210 Morrall, P. G. 104 Mortreux, A. 36 Moulijn, J. A. 209 Muneer, M. 24 Murahashi, S.-I. 95 Murakoshi, Y. 152 Murata, K. 107 Murty, B. S. 47, 104 Murugesan, S. 47 Murzin, D. Yu. 178 Musiala, M. 207 Muthuraaman, B. 47 Mutolo, P. F. 210

Machado, G. 153 Madhavan, J. 47 Maeda, R. 152 Maes, B. U. W. 49 Makharia, R. 49 Makino, K. 49 Makkee, M. 177 Maldonado-Hódar, F. J. 209 Malecki, J. G. 47 Malliaras, G. G. 47 MaQuilon, S. 207 Marcaccio, M. 105 Marcinec, B. 36 Markus, H. 25 Martellaro, P. 207 Maruthamuthu, P. 47 Masuda, T. 36, 210 Matsumoto, F. 210 Matthew, J. A. D. 46 Matthey, J. 208 Matveev, S. A. 29

Nagashima, H. 96 Naldrett, A. J. 13 Natta, G. 36 Ndifor, E. N. 209 Nelson, A. J. 104 Neumann, M. 150 Neurock, M. 23 Niemantsverdriet, H.196 Nikfarjam, A. 105 Nishimura, C. 152 Nishiyama, H. 95


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Noels, A. F. Nolan, S. P. Noyori, R. Nuithitikul, K. Nuyken, O.

36 36 95, 107 210 48

O’Brien, C. J. Ohkubo, K. Okajima, K. Organ, M. G. Ota, K.-I. Ou, Z. Ozeki, T.

209 69 49 209 107 150 207

Paatero, E. 106 Pacurariu, R. 150 Palazzi, A. 105 Pan, M. 49 Panarello, A. P. 48 Paolucci, F. 105 Park, C. R. 208 Park, G. S. 204 Parmon, V. N. 22 Pascal, R. A. 47 Pascut, L. G. 150 Pawelec, B. 152 Peng, J. 47 Pérez-Cadenas, A. F. 209 Perng, T.-P. 207 Persson, K. 66 Petch, M. I. 21 Peterson, E. S. 207 Pettersson, L. J. 25 Pfaff, C. 48 Pham, L. 207 Piccolo, L. 26 Pinhero, P. J. 207 Pink, C. J. 153 Piqueras, C. M. 152 Podyacheva, O. Yu. 22 Pontonnier, L. 150 Pop, V. 150 Poquillon, D. 47 Pöttgen, R. 46, 150 Pottlacher, G. 144 Poulston, S. 22 Prins, R. 25 Quesada, R. Rabiei, A. Ragauskas, A. J.

47 105 106

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Ralph, T. R. Rehren, Th. Ren, B. Rendina, L. M. Reynolds, J. R. Riecken, J. F. Risch, N. Roberts, W. Rodik, R. Rodriguez, K. J. Rodríguez, R. Rohl, R. Rolf, S. Rombouts, G. Rooney, J. J. Rossi, M. Rotello, V. M. Roundy, E. Roy, A. G. Roychowdhury, C. Rudenko, V. K. Rugmini, S. Rushforth, R.

200 120 208 104 151 46 208 194 104 107 48 47 204 49 36 194 49 152 107 210 29 196 197

Sabirianov, R. F. Sadigh, B. Sadykov, V. A. Saeed, I. Saito, A. Sakamoto, K. Sakamoto, M. Salehi, A. Salomons, S. Sao Joao, S. Saotome, H. Sarova, G. H. Sato, S. Sato, Y. Savadogo, O. Schanze, K. S. Scheckenbach, C. Scherer, G. Schlogl, R. Schluga, P. Schmehl, R. Schmidt, L. D. Schmidt, T. Scholz, U. Schönfelder, D. Schrock, R. R. Schuster, D. I. Schütz, J.

153 104 64 210 48 46 48 105 66 26 48 150 207 48 107 151 158 203 23 49 151 106 203 106 48 35 150 150

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Seol, H.-J. Seymour, R. Sha, J. B. Shaikhutdinov, S. Shao-Horn, Y. Shapley, J. R. Shekhtman, S. Shen, M. Shi, J.-C. Shi, Z. Shido, T. Shimura, Y. Shinar, J. Shinar, R. Shiotsuki, M. Shukla, N. Siani, A. Silva, S. R. P. Simm, A. O. Simonet, J. Simplicio, L. M. Singh, A. K. Siroma, Z. Sjunnesson, L. Slinker, J. D. Smith, A. Smith, C. J. Smith, P. Sodeoka, M. Solonenko, O. P. Soltner, T. Son, K.-H. Song, J. M. Song, M. Y. Spangler, L. Spitsberg, I. Stafyla, E. Stagni, S. Stahl, S. S. Steel, M. C. F. Steichen, E. Steinhoff, B. A. Steinmann, P.-A. Stelzer, F. Stieglitz, A. Stimming, U. Stone, C. Streck, R. Strobel, R. Ströbel, R. Su, H. L. Sudoh, M.

49 27 46 195 49 152 195 105 153 151 48 210 151 151 210 107 152 207 105 180 66 106 210 38 47 22 48 112 210 22 46 49 210 208 207 105 152 105 153 205 78 153 208 36 78 204 202 36 22 203 46 49

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Sugimura, Y. Sulman, E. Sun, P. Sunley, G. J. Surareungchai, W. Susanti, D. Suwinska, K. Suzuki, H. Suzuki, K. Suzuki, S. Suzuki, T. Szpunar, J. A.

46 25 150 150 47 151 104 96 207 210 210 151

Tada, M. Takács, A. F. Takahashi, K. Takano, H. Takao, T. Takenaka, T. Tanaka, Y. Tandon, P. K. Tang, H. Tang, N. J. Tang, S. L. Taniguchi, A. Tat, F. T. Tatarinova, G. N. Taylor, R. A. Taylor, S. H. Tennant, S. Terada, Y. Tester, J. W. Thomas, B. Thomas, J. M. Thomas, S. Thompsett, D. Thorn-Csanyi, E. Tian, Z.-Q. Tillmetz, W. Timerbaev, A. R. Timofeev, A. N. Toganoh, M. Tokunaga, T. Tonetto, G. M. Torbati, R. Trasatti, S. Trasatti, S. P. Trnka, T. M. Tronconi, E. Trueba, M. Truett, W. E. Tsai, D.-S.

48 150 207 210 96 46 48 106 49 46 46 210 150 29 150 209 77 69 48 105 152 152 21 36 208 38 49 29 150 207 152 64 151 151 95 106 151 36 151


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Tsang, M. W. S. 48 Tsang, S. C. 21 Tsao, C. S. 107 Tsaprailis, H. 153 Tsuchiya, Y. 210 Tsymbal, E. Y. 153 Tsymbal, L. 104 Turner, P. 104 Twigg, M. V. 65, 179 Uchida, H. Uchida, I. Umeda, M.

48, 210 210 210

Vahlas, C. Valente, C. Valetsky, P. Valldor, M. Vassylyev, O. Vayenas, C. Vazquez-Gomez, L. Venturi, M. Verpoort, F. Vigier, F. Virgilio, J. A. Vlassak, J. J.

47 209 25 150 48 26 208 40 36 104 48 46

Wagener, K. 36 Wang, G. 151 Wang, J. 105 Wang, K.-W. 207 Wang, R. L. 46 Wang, T. 209 Wang, X.-P. 153 Ware, M. 78 Warren, S. C. 210 Watanabe, M. 48, 210 Waugh, K. 195 Weberskirch, R. 48 Weiland, R. 158 Weiss, K. 36 Wells, R. 20 Werner, H. 208 Werth, C. J. 152 White, A. J. P. 150 White, M. 43 White, P. 206 Wiesner, U. 210 151 Wijeratne, N. R. Williams, J. A. G. 104 Williams, K. A. 106 Williams, V. A. 209

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Williams, W. M. 207 Wilson, S. R. 150 Winter, A. 208 Winterbottom, J. M. 210 Witte, J. 158 Wiyaratn, W. 47 Wollaston, W. H. 77 Wong, H. 153 Wu, C.-J. 105 Wu, D.-Y. 208 Wu, S. 151 Wynne, K. J. 153 Xia, D. Xie, B. Xiong, Y. Xu, H. Xu, N.

107 48 48 152 209

Yamabe-Mitarai, Y. Yamaguchi, K. Yamamoto, Y. Yamashita, H. Yang, P.-Y. Yap, T. Yasuda, K. Yeh, W.-C. Yeh, Z.-H. Yermakov, A. V. Yeung, C. M. Y. Yin, J. Young, D. P. Yu, C.-H. Yu, H.-W. Yu, K. Yu, K. M. K. Yu, S.

46 209 95 48 153 196 210 151 105 29 21 106 207 49 153 208 21 208

Zacchini, S. 105 Zeldovich, V. B. 210 Zhang, H. 153 Zhang, J. 105, 152 Zhang, L. 107 Zhang, Q. G. 207 Zhang, S. 150 Zhang, W. 46 Zhang, X. 207 Zhang, Y. 47, 152 Zheng, J. 208 Zhou, J. 208 Zhou, Z. 150, 151 Ziolkowski, E. J. 104

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SUBJECT INDEX TO VOLUME 50 Page

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a = abstract Acetic Acid, from syngas, a 209 Acetylenes, hydrogenation, selective 156 polymerisation, a 210 ADMET, production of specialty polymers 81 Alcohols, aryl, coupling, of amines, a 106 benzyl, oxidation, a 106 cyclohexanol, oxidation, a 106 EtOH, from Fischer-Tropsch reaction 22 MeOH, electrooxidation, a 107, 153 fuel, for fuel cells 38 oxidation, a 210 reforming 22 sensor, a 152 oxidation, aerobic, a 153, 209 Aldehydes, aromatic, oxidation, a 106 Alkanes, oxidation, partial, a 106 propane, dehydrogenation 22 Alkenes, metathesis 35 Alkylation, asymmetric allylic, a 48 Alkynes, addition, to cyclopropenes, a 106 cyclisation 171 hydrogenation 22, 194 Amination, aryl, in sc-CO2, a 48 Buchwald-Hartwig, a 49 Amines, coupling, of aryl alcohols, aryl halides, a 106 oxidation, aerobic, a 209 2– Aniline, oxidation, by PtCl6 , a 151 Aromatisation, pyrolysis gasoline 194 Aryl Halides, in reactions, a 48, 106, 153 N-Arylation, N-silyl derivatives, a 48 Arylboronic Acids, Suzuki-Miyaura couplings, a 153

Catalysts, (cont.) deactivation, in catalyst design 22 electrochemical promotion 22 improving service life 52 N2O greenhouse gas abatement 103 poisons, Hg, removal 156 S species 110 recycling, a 48, 106, 153, 209 S additions, activity control 110 supported, application, characterisation, preparation 20 three-way, see Three-Way Catalysts Catalysts, Iridium, Co/alumina, + Ir, Fischer-Tropsch 22 electrocatalysts, PtIrCo, for PEMFCs 202 Catalysts, Iridium Complexes, Ir phosphine, cyclisation of alkynes 171 [Ir(COE)2Cl]2/dppe, methyl oleate hydroboration, a 210 Ir(III) N-heterocyclic carbene, H transfer reduction 171 Catalysts, Palladium, Au-Pd, oxidation of CO, + H2 194 synthesis of H2O2 194 AuPtPd/SiO2-Al2O3, naphthalene hydrogenation, a 152 coupling of aryl alcohols, aryl halides, + amines, a 106 electrocatalysts, Pd-Co, Pd-Cr, Pd-Ni, for DMFCs, a 107 Pd, addition, TiO2, degradation of organics 22 + Ag, hydrogenation of acetylene 194 CH4 combustion 64 foil, pentyne hydrogenation 22 for motorcycles, a 105 oxidative reactions, diesel, gasoline 64 S-poisoned, regeneration, for CH4 combustion 177 surfaces, pentyne hydrogenation 22 Pd + Au/alumina (from Ni3Al (111) single crystal) 22 Pd monolith + Pt/Rh/Ce monolith TWC 177 Pd nanoparticles-polymer, fine chemicals synthesis 22 Pd shell-Ni core/MgO, butadiene hydrogenation 22 CO oxidation 22 Pd(111), single crystal, pentyne hydrogenation 22 Pd/Al2O3, CH4 combustion 64 Pd/γ-Al2O3, hydrogenation of sunflower oil, a 152 Pd/γ-Al2O3 on metallic foams, washcoating method, a 106 Pd/Al2O3/metal foil, CH4 combustion 22 Pd/Al18B4O33, CH4 combustion 64 Pd/alumina, Hg posioning 156 hydrogenation of acetylenes 156 hydrogenation of dibenzothiophenes 22 pentyne hydrogenation 22 Pd/C, hydrogenation of alkynes 194 Pd/C/asymmetric α-Al2O3 membrane, H2O2 synthesis 22 Pd/C-coated monoliths, combustion of xylenes, a 209 Pd/polymer fibres, hydrogenation of sterols, a 106 Pd/TiO2, nitrate hydrogenation 22 Pd/TiO2 (P25), reforming MeOH, using UV 22 Pd-TiO2 film, oxidation of formic acid, a 48 Pd/zeolite, matairesinol production 22 – Pd-Cu/γ-Al2O3, NO3 reduction, a 152 22 Pd-Mn/Al2O3/metal foil, CH4 combustion Pd-Pt, CH4 combustion 64 diesel oxidation 177 S-poisoned, regeneration, for CH4 combustion 177 Pd-Pt/alumina, hydrogenation of dibenzothiophenes 22 Pd-Pt/Ce-ZrO2, CH4 combustion 64 PdPt nanoparticles-, PdZn nanoparticles-polymer 22 PdO/Al2O3, CH4 combustion 64 Pt-Pd/Al2O3, CH4 combustion 64 PtPd/C MWNTs, naphthalene hydrogenation, a 152 PtPd/SiO2-Al2O3, naphthalene hydrogenation, a 152 Catalysts, Palladium Complexes, Pd, Suzuki couplings, microwave-promoted, a 209 Pd carbenes + poly(2-oxazoline)s, couplings, in H2O, a 48 Pd enolates, chiral, enantioselective fluorination, a 210 Pd(II) + N ligands/SiO2, Suzuki couplings, a 48 Pd2dba3 + X-Phos, amination reactions, in sc-CO2, a 48 Pd2(dba)3-CHCl3, Suzuki couplings, a 153

Biaryls, by Suzuki coupling, a 106 Biomolecules, sensor, a 105 Book Reviews, “Electrodeposition of the Precious Metals” 67 “Principles of Fuel Cells” 200 “Ruthenium in Organic Synthesis” 95 “Supported Metals in Catalysis” 20 Brazil, PGEs, geology 13, 134 Buchwald-Hartwig Couplings, microwave-assisted, a 49 Bushveld Complex 130, 134 Cancer, anti-, Pt complexes, a 49 Ru-pac complexes 2 Capacitors, RuO2/TiO2 nanorods, a 208 Carbenes 35, 48, 104, 150, 153, 171, 209 Carbocycles, synthesis, through metathesis 81 Carbon Oxides, CO, hydrogenation, a 209 oxidation 22, 106, 152, 177 selective 22, 48, 152, 194 as probe for Pt 21 tolerance, of PEMFC anodes 200 CO2, reduction, Ru catalysis 95 supercritical, solvent, a 48 tolerance, of PEMFC anodes 200 Carbonylation, Ru catalysis 95 Carbonyls, reduction, to alcohols, a 209 Carboxylic Acids, formic, oxidation, a 48 Catalysis, asymmetric 54, 107 book reviews 20, 95 conferences 22, 64, 177, 194 François Gault Lectureship, Johnson Matthey Award 22 fundamental studies; theoretical methods 22 heterogeneous, a 48, 105–106, 152, 209 homogeneous, a 48–49, 106–107, 153, 209–210 metathesis reactions, 2005 Nobel Prize for Chemistry 35 by supported metals 20 Catalysts, activity, test: microreactor; pilot plant 52 book reviews 20, 95 conferences 22, 64, 177, 194 contaminant levels 52


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Catalysts, Palladium Complexes, (cont.) [Pd(η3-C3H5)Cl]2 + chiral fluorous aminophosphine, asymmetric allylic alkylation, a 48 209 PdCl2 + PEPPSI-IPr, Negishi reaction, a Pd(DPPF)Cl2, Suzuki coupling, aryl bromides, a 106 Pd(OAc)2 + 2-(di-t-butylphosphanyl)biphenyl, a 49 Pd(OAc)2 + 2-(dicyclohexylphosphanyl)biphenyl, a 49 Pd(OAc)2 + imidazolium salt, SM couplings, a 153 Pd(OAc)2/DMSO + MS3A, alcohol oxidation, a 153 Pd(OAc)2/[(Me)3PH]BF4/Et3N, addition of alkynes, a 106 Pd(OAc)2/P(OCH3)3, Heck coupling, a 48 Pd(OAc)2/pyridine + MS3A, alcohol oxidation, a 153 Pd–phosphine, addition of alkynes, a 106 Catalysts, Platinum, AuPtPd/SiO2-Al2O3, naphthalene hydrogenation, a 152 BaO/Pt(111), NOx storage 177 CeO2-encapsulated Pt, -encapsulated Pt/Au, WGSR 21 Co/alumina, + Pt, Fischer-Tropsch reaction 22 electrocatalysts, Au/Pt, anodes, for AFCs 38 Pt, for fuel cells 38, 107, 200 polycrystalline, electrode, MeOH oxidation, a 107 porous, electrode, for nano fuel cells, a 107 Pt black layer, MEA, for PEMFCs, a 210 Pt nanoparticles, MeOH oxidation, a 210 Pt nanoparticles/Nafion, for PEMFCs, a 49 Pt/C, cathodes, for AFCs 38 MEA, for fuel cells, a 210 for PEMFCs 49, 202 Pt/C black, cathodes, for PEFCs, a 210 Pt/C cloths, cathodes, for DMFCs, a 49 Pt/SWCNTs, cathodes, for DMFCs, PEMFCs, a 107 Pt/Vulcan XC 72, thermal stability, a 153 Pt/Vulcan XC 72/Nafion layer, thermal stability, a 153 PtBi nanoparticles, MeOH oxidation, a 210 PtCo, for PEMFCs 202 PtCo/C, cathodes, for PEMFCs 202 PtIrCo, for PEMFCs 202 PtMo, anodes, for PEMFCs 200 PtMo/C, anodes, for PEMFCs, a 49 PtPb nanoparticles, MeOH oxidation, a 210 PtRu, anodes, for AFCs 38 anodes, for PEMFCs 200 for DMFCs 38, 202 Pt/Ru/C, electrodes, for DMFCs 38 PtRu black, anodes, for DAFCs 202 PtRu nanoparticles, MeOH oxidation, a 210 PtRuIr/C MWNTs, anodic oxidation of MeOH, a 153 PtSb, MeOH electrooxidation, a 107 PtSn, for DAFCs 202 Pd monolith + Pt/Rh/Ce monolith TWC 177 Pd-Pt, CH4 combustion 64 diesel oxidation 177 177 S-poisoned, regeneration, for CH4 combustion Pd-Pt/alumina, hydrogenation of dibenzothiphenes 22 Pd-Pt/Ce-ZrO2, CH4 combustion 64 PdPt nanoparticles-polymer, fine chemicals synthesis 22 Pt, addition, TiO2, degradation of organics 22 catalytic reforming units 52 hydrogenation of alkyl pyruvates, + ionic liquids 194 for motorcycles, a 105 Olefex process (propane to propylene) 22 oxidative reactions, diesel, gasoline 64 propane dehydrogenation 22 for reforming 110 soot + NO + O2 177 Pt coated Na-β''-alumina, NOx storage device 22 Pt/Al2O3, + AE oxide, NOx storage-reduction, a 105 pyrolysis gasoline, aromatisation, hydrogenolysis 194 + RE oxide, NOx storage-reduction, a 105 soot + NO2 + O2 177 Pt/γ-Al2O3 + V, naphthalene oxidation, a 209 Pt/alumina, hydrogenation of dibenzothiophenes 22 Pt/Ba/Al2O3, by one-step flame synthesis 22 NOx storage 22 NOx storage/reduction 177

Catalysts, Platinum, (cont.) Pt/Ba/CeO2, NOx storage/reduction 177 Pt/Ba/CeZr, NOx storage 177 Pt/C-coated monoliths, combustion of xylenes, a 209 21, 22, 194 Pt/CeO2, WGSR Pt/ceria-zirconia oxide, + Gd, La, Sm, CH4 oxidation 64 Pt/CeZr, NOx storage 177 Pt/mordenite, oxidation of CO, in H2, a 48 Pt/SiO2, CO oxidation, a 152 Pt/TiO2 (rutile), preparation, effect of Pt precursor, a 152 WGSR, at low-temperature, a 152 Pt/TiO2 thin film, visible light-responsive 22 Pt/YSZ, monolith-type reactor 22 Pt-Ce, soot + NO + O2 177 Pt-Fe, + Na-A zeolite, oxidation of CO, in n-butane 22 Pt-Fe/mordenite, oxidation of CO, in H2, a 48 PtFe/SiO2, CO oxidation, a 152 PtFe2/SiO2 cluster-derived, CO oxidation, + H2, a 152 Pt5Fe2/SiO2, cluster-derived, CO oxidation, + H2, a 152 Pt-Pd/Al2O3, CH4 combustion 64 PtPd/C MWNTs, naphthalene hydrogenation, a 152 PtPd/SiO2-Al2O3, naphthalene hydrogenation, a 152 Pt-Re, catalytic reforming units 52 Pt-Rh gauze pack 103 Pt-Sn/HZSM-5 zeolite, denitration of drinking H2O, a 48 Catalysts, Rhodium, Pt-Rh gauze pack 103 Pt/Rh/Ce monolith TWC 177 Rh, oxidative reactions, diesel, gasoline 64 Rh coated K-β''-alumina, Fischer-Tropsch reaction 22 Rh-coated foams, alkane oxidation, a 106 Rh nanoparticles, hydroformylation of olefins, a 153 Rh nanoparticles/nanosized SiO2, CO hydrogenation, a 209 Rh/C, hydroformylation of olefins, a 153 Rh/LaMnO3, CH4 combustion 64 Rh/YSZ, monolith-type reactor 22 Rh-Ce-Mn/SiO2 + CNTs, CO hydrogenation, a 209 Catalysts, Rhodium Complexes, Rh, + β-diiminate, + NH3 ligands, + phenoxy-imine, polymerisation of acetylenes, a 210 Rh/BINOL, asymmetric hydrogenation 54 Rh/MonoPhos ligands, asymmetric hydrogenation 54 Rh phosphine, cyclisation of alkynes 171 Rh/phosphoramidites, asymmetric hydrogenation 54 RhCl(TPPTS)3/SiO2, cinnamaldehyde hydrogenation, a 210 Rh(COD)2BF4 + phosphoramidites 54 [Rh(cod)Cl]2, a 210 Rh(III) N-heterocyclic carbene, H transfer reduction 171 [Rh(nbd)Cl]2, a 210 Rhodium Bicentenary Competition, research 171 Catalysts, Ruthenium, carbonylations 95 Co/alumina, + Ru, Fischer-Tropsch reaction 22 95 CO2 reductions electrocatalysts, PtRu, anodes, for AFCs 38 anodes, for PEMFCs 200 for DMFCs 38, 202 Pt/Ru/C, electrodes, for DMFCs 38 PtRu black, anodes, for DAFCs 202 PtRu nanoparticles, MeOH oxidation, a 210 RuSe, cathodes, for DAFCs 202 Fischer-Tropsch reactions 95 oxidations 95 RuCl3, with H2O2, oxidation of organics, a 106 Ru(OH)x/Fe3O4, aerobic oxidations; reductions , a 209 separation, with a permanent magnet, a 209 Catalysts, Ruthenium Complexes, π-allyl-Ru 95 chiral, in asymmetric synthesis, a 107 Grubbs’ catalysts, first, second generation 35 in organic synthesis 95 Ru alkylidenes bearing N-heterocyclic carbenes 35 Ru allenylidenes, cationic, neutral 81 metathesis, ADMET, enyne, RCM, ROMP 81 Ru carbene, asarone-derived, olefin metathesis, a 106 ruthenacycle intermediates, in C–C bond formation 95 Cinnamaldehyde, hydrogenation, a 210 Cisplatin, dinuclear analogues, DFT/CDM study, a 107


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Coatings, Al-Pt, on Ti6242, a 47 thermal barrier, with PtNiAl diffusion bond coats, a 105 Combustion, catalytic, VOC emissions 64 22, 64, 177 CH4 xylenes, a 209 Composites, Pt-polyaniline, synthesis, a 151 Conferences, 9th Grove Fuel Cell Symp., London, 2005 38 10th International Platinum Symposium, Finland, 2005 13 10th Ulm Electrochemical Talks, Germany, 2006 202 CAPoC7, Brussels, 2006 177 EUROPACAT-VII, Bulgaria, 2005 22 IWCC6, Isle of Ischia, Italy, 2005 64 SURCAT 2006, Cardiff, 2006 194 Coupling Reactions, industrial-scale, a 106 Creep, Ir, high temperature 158 ® CRT , for diesel emission control 177 Crucibles, Ir 29, 158 Crystallographic Properties, Pt 118 CVD, Pd, Pd-Pt bilayer, Pt, films, on polyimide, a 208 Cyclisation, alkynes 171 Cycloolefins, ROMP 81 Cyclopropanation, Ru catalysis 95 Cyclopropenes, addition of alkynes, a 106

Films, FePt nanocubes, a 107 Pd, Pd-Pt bilayer, Pt, on polyimide, a 208 platinised Pt, reduction 180 polypyrrole, + Ir, Pt, Ru particles, H evolution, a 151 ‘Final Analysis’ 52, 110, 156 Fine Chemicals, synthesis 20 Fischer-Tropsch Reactions, Rh coated K-β''-alumina 22 Ru catalysis 95 2+ 150 Fluorescence, [Ru(bpy)(bpy-C60)] , a Fluorination, enantioselective, a 210 Fracture, Ir 158 Fuel Cells, a 49, 107, 153, 210 AFC 38, 200 book review 200 conferences 38, 202 DAFC, electrocatalysts 202 DMFC, electrocatalysts 107, 200, 202 electrodes 38, 49, 107, 202 electrooxidation, MeOH, a 107 ORR, a 49 electrocatalysts 38, 153, 210 electrochemical losses 200 fuels 22, 38, 152, 200, 202 Fuel Cell Knowledge Transfer Network 119 MCFC 200, 202 membrane electrode assemblies 38, 49, 107, 200, 202, 210 nano, a 107 PAFC 200 PEFC, Pt/C black + Nafion ink, a 210 PEMFC, anodes 49, 202 CO tolerance, CO2 tolerance 200 cathodes 107, 202 electrocatalysts 38, 49, 200, 202 Pt/Vulcan XC 72/Nafion layer, thermal stability, a 153 power, auxiliary supplies 22, 38 consumer electronics 38 Pt, availability, recovery, recycling 38 SOFC 200 transport, road vehicles: buses, cars, motorbikes 38 Fuels, H2 22, 38, 48, 152, 202 MeOH 38 for motorcycles, a 105

Dehydrogenation, propane 22 Denitration, drinking H2O, a 48 Dental, Au-Ag-Pd-In alloy, precipitation hardening, a 49 Deposition, Ag–Pd films, a 208 electroless, Pd nanowires, a 151 electrostatic spray, Pt/C MEA, a 210 photocatalytic, Pd membranes, a 209 TiPdNi thin films, a 105 Dibenzothiophenes, hydrogenation 22 Dienes, butadiene, hydrogenation 20, 22 Diesel, oxidation catalysts 64, 177 Diffusion, volume, Au, into single crystal Ir 29 Diffusion Couples, Sn/Pd/Sn, a 46 Electrical Conductivity, Magnus’ salt derivatives, fibres112 Electrical Contacts, ohmic, Ni/Pd, oxidised; Pd, a 153 Schottky, Pd/GaAs, Pd/porous-GaAs, H sensing, a 105 Electrical and Electronic Engineering, a 107, 153 Electrical Resistivity, Pd 144 Electrochemical Promotion, catalysts 22 Electrochemistry, a 47, 151, 208 cathode reactivity, of platinised Pt, in super-dry DMF 180 polymerisation, C2H2, a 208 [Ru(bpy)(bpy-C60)]2+, [Ru(tpy)(tpy-C60)]2+, a 150 synthesis, Pt-polyaniline composite, a 151 Zr-Pd, Zr-Pt, in different solutions, a 47 Electrodeposition, Ir, Os, Rh, Ru 67 Pt-Cu nanowires, a 107 208 RuO2, on electrospun TiO2, a Electrodeposition & Surface Coatings, a 47, 105, 151, 208 Electrodes, in fuel cells, see Fuel Cells micro-, array, Pd plated B-doped diamond, a 105 Pd nanoparticles/B-doped diamond, a 105 platinised Pt, cathode, reactivity, in super-dry DMF 180 polypyrrole films, + Ir, Pt, Ru particles, H evolution, a 151 Pt, with ferroelectric films, a 153 Pt-Zn porphyrin nanocomposite/Nafion/glassy C, a 47 Rh, roughened, polymerisation of C2H2, a 208 RuO2–IrO2–SnO2/Ti, preparation, characterisation, a 208 RuO2/TiO2 nanorods, a 208 SrRuO3, with ferroelectric films, a 153 Electroless Plating, Ir, Os, Pd, Pt, Rh, Ru, Pt-Rh 67 Pd nanowires, a 151 Electrospinning, Magnus’ salt derivatives, to fibres 112 Elongation, by tensile tests, Pt-Cu, Pt-Ru 15 Emission Control, motor vehicles 64, 177 VOCs, catalytic combustion 64 Enthalpy of Fusion, Pd 144 Enyne Metathesis, in synthesis 81 Fibres, Magnus’ green salt derivatives


112

Gasoline, emissions, catalytic oxidation Gauzes, Pt-Rh Geology, Pt

64 103 13, 130, 134

Hardening, Ir-Hf-Nb, a 46 precipitation, Au-Ag-Pd-In, a 49 Heat Capacity, isobaric, Pd 144 Heck Reactions, a 48 Heterocycles, synthesis, through metathesis 81 High Pressure, synthesis, CePtSn, a 46 High Temperature, mechanical properties, Ir 158 synthesis, CePtSn, a 46 69 ultra-, Rh3X, thermophysical properties High Throuhput Screening, ligands, used in catalysis 54 History, Frédéric Joliot-Curie, Iréne Joliot-Curie 97 Hans Merensky 130 Ir discovery, Smithson Tennant, commemorative plaque 77 metathesis, alkenes 35 Os discovery, commemorative plaque 77 Pd isotopes, discoverers 97 Pd print, Alfred Steiglitz; platinotype, Edward Steichen 78 Pt, discovery, in the Bushveld Complex 130 Pt, roubles, production, refining 120 Hydrazine, sensor, a 105 Hydroboration, methyl oleate, a 210 Hydrocarbons, oxidation 64, 106 processing applications 110 Hydrodearomatisation, pgm/alumina 22 Hydrodesulfurisation, pgm/alumina 22 Hydroformylation, solventless, olefins, a 153 Hydrogen, absorption, into Pd81Pt19 foil, a 104 displacement, from Pd, by noble gases, a 46

219

Page Hydrogen, (cont.) evolution, from polypyrrole, + Ir, Pt, Ru particles, a 151 fuel 22, 38, 48, 152, 202 isotope separation, a 208 microwave plasma irradiation, Co-Pd, a 207 permeation, of Pd membranes, a 152, 208, 209 presence, CO oxidation 48, 152, 194 production 20, 22, 47 sensor, a 105 Hydrogen Peroxide, + RuCl3, oxidation of organics, a 106 synthesis 22, 194 Hydrogenation, alkyl pyruvates 194 alkynes 194 asymmetric 54 asymmetric transfer, a 107 butadiene 20, 22 cinnamaldehyde, a 210 CO, a 209 dibenzothiophenes 22 naphthalene, a 152 nitrates, in H2O 22 in organic synthesis 95 pentyne 22 selective, acetylenes 156 sterols, a 106 sunflower oil, a 152 transfer, in organic synthesis 95 α,β-unsaturated carbonyl compounds 20 Hydrogenolysis, hydroxymatairesinol 22 pyrolysis gasoline 194 Imines, transfer hydrogenation, asymmetric, a 107 Ionic Liquids 153, 194 Iridium, creep, high temperature 158 crucibles 29, 158 discovery, commemorative plaque 77 electrodeposition, electroless deposition 67 high-temperature mechanical properties 158 impurities, mass transfer 29 particles, in polypyrrole films, H evolution, a 151 single-Ir, volume diffusion of Au 29 stress-rupture strength, high temperature 158 tensile strength, high temperature 158 vacancy-impurity complexes, growth 29 Iridium Alloys, Ir-Hf-Nb, hardening behaviour, a 46 superalloys, refractory, a 46 Iridium Complexes, Ir N-heterocyclic carbenes 171 trans-[IrCl(C8H14)(PiPr3)2] + benzene, a 208 IrCl(CO)2(p-toluidine) + tetraphenylporphyrin, a 150 [Ir(dF(CF3)ppy)2(dtbbpy)](PF6), electroluminescene, a 47 photoinduced H2 production, a 47 208 [IrH2(Cl)(PiPr3)2], preparation, a [IrH(C6H3F2)(Cl)(PiPr3)2], preparation, a 208 [IrH(C6H4X)(Cl)(PiPr3)2], preparation, a 208 [IrH(C6H5)(Cl)(PiPr3)2], preparation, a 208 [IrH{(C6H3F(CH3)}(Cl)(PiPr3)2], preparation, a 208 Ir(I), inverted N-confused porphyrin, a 150 Ir(III), bis-terpyridyl/pyridyl groups, luminescence, a 104 (MeCp)Ir(COD), precursor for MOCVD, a 151 Iridium Compounds, Ir nitride, synthesis, a 104 IrO2 nanorods, by MOCVD, a 151 RuO2–IrO2–SnO2/Ti electrodes, a 208 Isomerisation, methyl oleate, a 210 organic substrates, Ru catalysis 95 Isomerism, [Pt(SC(NH2)2)4][C5O5]·4DMSO crystals, a 47 Isotopes, Pd, discoveries 97 Johnson Matthey, Award for Innovation in Catalysis marketing, N2O abatement catalyst “Platinum 2006” Rhodium Bicentenary Competition Susan V. Ashton, retirement as Editor, a tribute

22 103 143 171 205

Ketones, H transfer reduction transfer hydrogenation, asymmetric, a

171 107


Page Kharasch Addition Reactions, Ru catalysis

95

Lignans, matairesinol production 22 Luminescence, bis-terpyridyl Ir(III), + pyridyl groups, a 104 47 electro-, [Ir(dF(CF3)ppy)2(dtbbpy)](PF6), a Ru(II) polypyridyls, containing 5-aryltetrazolates, a 105 Magnetism, Ce(Pd1–xAgx)2Al3, a 150 CePtSn, a 46 FePt nanoparticles, a 49 FePt/Fe composite nanotubes, a 46 MnxPd1–x, a 150 [Ru(C9H6NO)3]·MeOH, a 47 in separation of Ru(OH)x/Fe3O4, a 209 TbRhIn5, a 207 MEAs 38, 49, 107, 200, 202, 210 Mechanical Properties, high temperature, Ir, a 158 Pt-5 wt.% Cu, Pt-5 wt.% Ru 15 Medical Uses 2, 49, 107 Membranes, Pd, H2 permeation, a 152 microfabrication, a 152 permeation, for H isotope separation, a 208 Pd/C coated asymmetric α-Al2O3, H2O2, synthesis 22 Pd/TiO2, by photocatalytic deposition, a 209 reactor; series; Pd, in H2 generation, a 152 Metallopharmaceuticals, Ru polyaminocarboxylates 2 Metathesis 35, 81, 95, 106 Methane, combustion 22, 64, 177 emissions, oxidation 64 Methyl Oleate, hydroboration, isomerisation, a 210 Microwaves, in organic synthesis, a 49, 209 plasma H irradiation, Co-Pd, a 207 MOCVD, Al-Pt coatings, on Ti6242, a 47 IrO2 nanorods, a 151 Nanocomposites, Pd-polyaniline, synthesis, a 152 Pt-Zn porphyrin, in detection of organohalides, a 47 Nanodroplets, fluorous, in organopalladium sphere, a 207 Nanofilms, polycrystalline Pt, thermal conductivity, a 207 Nanofiltration, solvents, a 153 Nanoparticles, FePt, a 49, 107 Pd, a 105, 151, 152 Pd70Ag30, a 207 Pt, a 47, 49, 210 PtBi, PtPb, PtRu, a 210 Rh, a 153, 209 Nanorods, IrO2, by MOCVD, a 151 Nanotubes, composite, FePt/Fe, a 46 Nanowires, Pt silicide, a 105 Pt-Cu, a 107 self-assembled, Pd, by electroless deposition, a 151 Naphthalenes, hydrogenation, a 152 oxidation, a 209 Naptha, reforming 20 209 Negishi Couplings, PdCl2 + PEPPSI-IPr, a Nitrates, in H2O 22, 48, 152 Nitric Acid, plants, N2O abatement catalyst 103 Nitrogen, from nitrate hydrogenation, in H2O 22 Nitrogen Oxides, N2O, abatement catalyst 103 NO, + O2, soot oxidation 177 scavengers, Ru-pac complexes 2 NO2, + O2, soot oxidation 177 NOx, HC SCR, NH3 SCR 177 lean, catalysis 22 storage 22, 177 storage-reduction 105, 177 trap, regeneration, by H2 22 Nobel Prize, Chemistry, metathesis reaction 35 Noble Gases, displacement of H, from Pd, a 46 Oil, sunflower, hydrogenation, a OLEDs, in O2 sensor, a Olefex Process, propane, to propylene Olefins, hydroformylation, solventless, a metathesis

152 151 22 153 81, 95, 106

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Optical Properties, Magnus’ salt derivatives, fibres 112 Organohalides, Negishi couplings, a 209 sensor, a 47 Osmium, discovery, commemorative plaque 77 electrodeposition, electroless deposition 67 Hf–Os system, thermodynamic assessment, a 104 patents 27 Oxidation, aerobic, alcohols, a 153, 209 amines, a 209 Al-Pt coatings, on Ti6242, a 47 aldehydes, aromatic, a 106 alkanes, a 106 aniline, a 151 benzyl alcohol, a 106 64 CH4 CO 22, 106, 152, 177 in n-butane 22 in presence of H2 48, 152, 194 cyclohexanol, a 106 electro-, MeOH, a 107, 153 enzymatic 2 formic acid, a 48 hydrocarbons 64, 106 MeOH, a 210 naphthalenes, a 209 Pd0.97Ce0.03, a 150 Ru catalysis 95 soot 177 Zr-Pd, Zr-Pt, a 104 Oxygen, reduction, in fuel cells, a 49, 107 sensors, a 151

Palladium Complexes, (cont.) [Pd(hypy)2]Cl2·2MeOH, crystal structure, a 207 Pd(II), with tetrazolecalix[4]arenes, a 104 phospha-palladacycle, with an acyclic carbene, a 104 Palladium Compounds, NbPdSi, structure, synthesis, a 150 Particulates, control 177 Patents 50–51, 108–109, 154–155, 211–212 Os 27 Phoscorite-Carbonatite Pipe Complexes, PGEs 134 Phosphoramidites, synthesis 54 Phosphorescence, electro-, PFO-PtTPP, a 47 Photocatalysis 22, 209 Photoconversion, a 47, 104–105, 151 Photoproperties, Magnus’ salt derivatives, fibres 112 Pt-acetylide polymer, a 151 2+ 151 [Ru(bpy)2(5-CNphen)] , a Ru(II) fullerene polypyridines, a 150 [(tpy)Ru(bis(U-terpyridine))Ru(tpy)]4+, a 208 [{(tpy)Ru}3(tris(U-terpyridine))]6+, a 208 Photoreactions, H2PtCl6/Zn porphyrin, + ascorbic acid, a 47 Photosensitisers, [Ir(dF(CF3)ppy)2(dtbbpy)](PF6), a 47 [Ru(bpy)2(5-CNphen)]2+, a 151 Plating Baths, Ir, Os, Pd, Pt, Pt-Rh, Rh, Ru 67 Platinotype, photograph, record price 78 Platinum, Al-Pt coatings, on Ti6242, a 47 availability, for fuel cells 38 “blackberry-like”, “cauliflower-like” structures 180 crystallographic properties 118 discovery, in the Bushveld Complex 130 electrodes, a 153 electroless deposition 67 film, on polyimide, a 208 geology 13, 130, 134 nanoparticles, a 47, 49, 210 particles, in polypyrrole films, H evolution, a 151 Pd-Pt bilayer film, on polyimide, a 208 platinised Pt films, reduction 180 polycrystalline, nanofilms, thermal conductivity, a 207 print, Edward Steichen, record price 78 production, history 120 Pt-polyaniline composite, synthesis, a 151 Pt/Co overlayers, adhesion, bonding, a 151 Pt/Ni overlayers, adhesion, bonding, a 151 reactions, with refractories 197 recovery, recycling, from fuel cells 38 refining, history 120 roubles 120 thermal expansion 118 thermal vacancy 118 thermocouples, maintenance, reliability, specification 197 Platinum Alloys, (Fe0.75P0.25)75B25, phase tranformations, a 46 FePt nanoparticles, self-assembly, a 107 surface PEGylation, a 49 FePt/Fe composite nanotubes, synthesis, a 46 104 Pd81Pt19 foil, H absorption, a PtBi nanoparticles, a 210 Pt-5 wt.% Cu, mechanical properties 15 Pt-Cu nanowires, electrodeposition, a 107 PtNiAl, diffusion bond coats, a 105 PtPb nanoparticles, a 210 Pt-Rh, electroless deposition 67 Pt-5 wt.% Ru, mechanical properties 15 PtRu nanoparticles, a 210 Rh-Pt thermocouples 197 Zr-Pt, electrochemical behaviour, in solution, a 47 oxidation, a 104 Platinum Complexes, bis(oxalato)platinate(II), PO, a 207 Me3(MeCp)Pt, for MOCVD, a 47 PFO-PtTPP, phosphorescence, a 47 – – + + [Pt2 , TAA , TAAX], [Pt4 , TMA , TMAX] 180 Pt-acetylide polymer, in solar cells, a 151 Pt-octaethylporphyrin, OLED-based O2 sensor, a 151 Pt(II), containing N-bonded acetamide, a 104 containing O-bonded acetamide, a 104 Pt(II) + aminoalcohol ligands, antitumour agents, a 49

Palladium, Ag–Pd films, tarnish resistance, a 208 electrical resistivity 144 electroless deposition 67 enthalpy of fusion 144 film, on polyimide, a 208 H displacement, by noble gases, a 46 isobaric heat capacity 144 isotopes, history of the discoveries 97 membranes 22, 152, 208, 209 nanoparticles, a 105, 151, 152 nanowires, self-assembled, by electroless deposition, a 151 ohmic contacts, oxidised Ni/Pd, Pd, a 153 Pd hydride, from Co-Pd, by microwave H plasma, a 207 Pd nanoparticles/B-doped diamond electrode, a 105 Pd plated B-doped diamond microdisc array, a 105 Pd-polyaniline nanocomposite, synthesis, a 152 Pd-Pt bilayer film, on polyimide, a 208 Pd/GaAs, /porous-GaAs, Schottky contact, a 105 print, Alfred Steiglitz 78 Sn/Pd/Sn diffusion couples, a 46 specific enthalpy 144 thermal conductivity 144 thermal diffusivity 144 thermophyical properties 144 150 Palladium Alloys, Ce(Pd1–xAgx)2Al3, magnetism, a Co-Pd, demixing, a 207 dental, Au-Ag-Pd-In, precipitation hardening, a 49 Fe-Pd shape-memory thin films, stress evolution, a 46 MnxPd1–x, preparation, magnetism, a 150 Pd0.97Ce0.03, oxidisation, a 150 Pd70Ag30 nanoparticles, preparation, a 207 Pd40Ni40B10P10, preparation, properties; Pd40Ni40P20, a 46 Pd81Pt19 foil, H absorption, a 104 PdSn2, PdSn3, PdSn4, a 46 TiPdNi thin films, shape memory effect, a 105 Zr-Pd, electrochemical behaviour, in solution, a 47 oxidation, a 104 Palladium Complexes, arrow shaped N-donor ligands, a 207 Pd-octaethylporphyrin, OLED-based O2 sensor, a 151 Pd2(η2-C60) structure, a 207 PdnC60, DFT calculations, a 207 [Pd(hypy)2]+, DFT modelling, IR spectroscopy, a 207 [Pd(hypy)2]Cl2, a 207


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Platinum Complexes, (cont.) [Pt(L)Me2], protonation, a 150 [Pt(L)Me(CH3CN)]+, by protonation, a 150 tetra(cyano)platinate(II), PO, a 207 Platinum Compounds, CePtSn, magnetism, a 46 cisplatin, dinuclear analogues, DFT/CDM study, a 107 Magnus’ salt derivatives, fibres, by electrospinning 112 Pt nitride, synthesis, a 104 Pt-silicide nanowires, biomolecule sensing, a 105 Pt-Zn porphyrin nanocomposites, synthesis, a 47 151 PtCl62–, oxidation of aniline, a reduction, a 151 [cis-{Pt(NH3)2}(μ-OH)]22+, a 107 [Pt(NH2dmoc)4][PtCl4], [Pt(NH2eh)4][PtCl4], fibres 112 [Pt(SC(NH2)2)4][C5O5]·4DMSO crystals, isomerism, a 47 Platinum Group Elements, geology 13, 130, 134 Pollution Control, flame combustion, fossil fuels 20 motor vehicles 177 photocatalysed degradation, organic pollutants 22 Polyaminocarboxylates, Ru complexes 2 Polymerisation, acetylenes, a 210 by metathesis 35, 81 electrochemical, of C2H2, a 208 Polymers, bis(oxalato)platinate(II), partial oxidised, a 207 Pd-polyaniline nanocomposite, synthesis, a 152 PFO-PtTPP, phosphorescence, a 47 polypyrrole films, + Ir, Pt, Ru particles, H evolution, a 151 Pt-acetylide polymer, in solar cells, a 151 Pt-polyaniline composite, synthesis, a 151 specialty, by ADMET, ROMP 81 synthesis, Ru catalysis 95 tetra(cyano)platinate(II), partial oxidised, a 207 Protonation, [Pt(L)Me2], a 150 Pyruvates, alkyl, hydrogenation, + ionic liquids 194

Russia, Pt 13, 130, 134 Ruthenium, electrodeposition, electroless deposition 67 particles, in polypyrrole films, H evolution, a 151 Ruthenium Alloys, Pt-5 wt.% Ru, mechanical properties 15 Ruthenium Complexes, [(C6H6)RuCl2]2 + quinolines, a 47 Ru polyaminocarboxylates, as antitumour drugs 2 as metallopharmaceuticals 2 as NO scavengers 2 as protease inhibitors 2 Ru(bpy)2(5-CNphen)]2+, photoproperties, a 151 [Ru(bpy)(bpy-C60)]2+, electrochemistry, fluorescence, a 150 [Ru(C9H6NO)3]·MeOH, magnetism, a 47 Ru(II) polypyridyls + aryltetrazolates, luminescence, a 105 2+ [Ru(tpy)(tpy-C60)] , electrochemical study, a 150 solar cells, a 47 4+ [(tpy)Ru(bis(U-terpyridine))Ru(tpy)] , photo, a 208 6+ [{(tpy)Ru}3(tris(U-terpyridine))] , photo, a 208 Ruthenium Compounds, RuO2, electrodeposition, a 208 electrodes, a 153, 208

RCM, in synthesis 81 Reactors, industrial, hydrogenation of sterols, a 106 membrane, Pd, in H2 generation, a 152 micro-, catalyst activity tests 52 monolith-type, YSZ, coated with Pt, Rh 22 pilot-plant, hydrogenation of sterols, a 106 Reduction, asymmetric, carbamates, enamides, enol acetates 54 to α-alkyl succinic acid derivatives 54 to α-amino acid, β-amino acid, derivatives 54 α,β-unsaturated acids 54 carbonyl compounds, a 209 CO2 95 H transfer, ketones 171 NO2–, NO3–, a 152 O, in fuel cells, a 49, 107 platinised Pt films 180 2– 151 PtCl6 , a Refining, Pt, history 120 Reforming, catalysts 52, 110 dimethyl ether 22 MeOH 22 naptha 20 Refractories, insulation, for Pt-based thermocouples 197 reactions, with Pt 197 Rhodium, electrodeposition, electroless deposition 67 electrodes, roughened, polymerisation of C2H2, a 208 nanoparticles, a 153, 209 Rhodium Bicentenary Competition, research 171 Rhodium Alloys, Pt-Rh, electroless deposition 67 Rh-Pt thermocouples 197 Rhodium Complexes, Rh N-heterocyclic carbenes 171 Rh(CO)2I(NHC), structure, a 150 Rh(COD)X(NHC), synthesis, structures, a 150 Rhodium Compounds, CeRhIn5, a 207 intermetallic, Rh3X (X = Hf, Nb,Ta, Ti, V, Zr), thermal conductivity, thermal expansion 69 TbRhIn5, crystal growth, magnetic properties, a 207 ROMP, cycloolefins; production of specialty polymers 81 Roubles, Pt 120


Selective Catalytic Reduction, HC, NH3 177 Sensors, biomolecules, a 105 H 2, a 105 hydrazine, a 105 MeOH, a 152 O 2, a 151 organohalides, a 47 Shape Memory Effect, Fe-Pd thin films, a 46 TiPdNi thin films, a 105 Single Crystals, Ir, volume diffusion of Au 29 Solar Cells, a 47, 151 Soot, oxidation 177 South Africa, Pt 13, 130, 134 Specific Enthalpy, Pd 144 Sputtering, co-, magnetron, of Ag–Pd films, a 208 Fe-Pd shape-memory thin films, a 46 Pt, on C cloths, a 49 Sterols, hydrogenation, a 106 Stress, by tensile tests, Pt-Cu, Pt-Ru 15 Stress-Rupture, strength, Ir, high temperature 158 Sulfur, catalyst poison 110 Superalloys, Ir-Hf-Nb, hardening behaviour, a 46 Supercritical Solvents, propane, in catalysis, a 152 Suzuki Couplings, a 48, 106, 153, 209 Suzuki-Miyaura Couplings, a 153 Syngas, in synthesis of acetic acid, a 209 Tensile, strength, high temperature, Ir Tetraalkylammonium Salts, influences on platinised Pt layers Thermal Conductivity, Pd polycrystalline Pt nanofilms, a Rh3X (X = Hf, Nb, Ta, Ti, V, Zr) Thermal Diffusivity, Pd Thermal Expansion, Pt Rh3X (X = Hf, Nb, Ta, Ti, V, Zr) Thermal Vacancy, Pt Thermocouples, Pt, reliability Thermophysical Properties, Pd Rh3X Thin Films, Ag–Pd, deposition, tarnish resistance, a Fe-Pd, shape memory, a TiPdNi, shape memory, a Three-Way Catalysts, ageing developments Vacancy-Impurity Complexes, growth, in Ir Vitamins, intermediates, synthesis VOCs, emissions, catalytic combustion Water, -soluble, FePt nanoparticles, a drinking, denitration Water Gas Shift Reaction Xylenes, combustion, a

158 180 144 207 69 144 118 69 118 197 144 69 208 46 105 177 177 29 22 64

49 22, 48 21, 22, 152, 194 209

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