In the past year both Toyota and Daimler Benz ... Daimler Benz. (Mercedes A-class) car is powered entirely by ...... ent g-factors and hfs constants, a, (due to cou-.
UK ISSN 0032-1400
PLATINUM METALS REVIEW A quarterly survey of research on t h e platinum metals and of developments in their npplication in industry
VOL. 42
JANUARY 1998
NO. 1
Contents HotspocMFuel Processor
2
By Stan Golunski
Acoustic Wave Enhancement of Catalytic Reaction Rates over Platinum Surfaces
8
By Sven Kelling and David A. King
Cold Platinum Cathode
10
The Development of Platino-Calixarenes
11
By Catherine Wieser-Jeunesse and Dominique Matt
Catalytic Reaction Guide
16
Contemporary Platinum Chemistry
17
By C. F. J. Barnard
New Studies in Fullerene Chemistry
18
By Viatcheslav1. Sokolov and Vasily V. Bashilov
Oxygen Dissociative Adsorption on Platinum Surfaces
24
Catalysts Play a Major Role in Development
25
By A. F. Chaffy
Development of the Noble MetaVOxide Coated Titanium Electrode
27
By P. C. S. Hayfield
Abstracts
34
New Patents
40
Communications should be addressed to The Editor, Susan V . Ashton, Plutinum Metals R e r i m Johnson Matthey Public Limited Compuny, Hatton Carden. Loitdon ECI N 8EE
HotSpotl'l Fuel Processor ADVANCING THE CASE FOR FUEL CELL POWERED CARS
By Stan Golunski Johnson Matthey Technology Centre
The number of rood vehicles in the world is set to double in the nezt twenfyyears. Such rapid growth threatens to destroy the clean air in regions where air pollution h a s not been a problem u p to now, and to reverse the improvements in air quality that have resulted from the use of catal-pic converters to clean-up exhaust emissions in t r a f f i congested areas. Thus, there is a compelling need to develop high effiiency passenger cars, free of emissions. One very promising option is the use of the fuel cell, which generates energy eflciently 6y converting hydrogen to steam. However, there are major drawbacks to carrying and using hydrogen on vehicles, including the complexities of re-fuelling and the absence of a so-called hydrogen economy Hydrogen fuelling of fuel-cell powered cars must & the ultimate goal and the most practical near-term solution is to use a n on-board fuel processor togenerate hydrogenfrom a liquid fwl while driving, and such a processor, the Hotspot'", is described here. An on-board fuel processor must be fast-starting, compact, efficient, responsive and clean. Most fuel processors meet several of these requirements, but the Hotspot' " technology developed by Johnson Matthey can meet them all. It combines the speed and compactness of partial oxidation with the efficiency of steam reforming. T h e balance between these two processes can be adjusted to respond to the different demands on the vehicle during use. The technology is simple to scale-up, and the maximum required output is achieved by combining in parallel the appropriate number of basic reactor units, see Figure 1. Although HotSpot'" produces some carbon monoxide, this can effectively be eliminated by a clean-up reactor. So far, the technology is most advanced for methanol processing, but the HotSpotl" concept is also being applied to hydrocarbon fuels.
The Need for HotSpotTH While the human population has doubled since 1950, the number of cars in the world has increased 7-fold (1). In North America, Western Europe and Japan, the growth rate in car population is expected to stabilise soon at about one
Placimni Metals Rev., 1998, 42, (l ), 2-7
per cent per year, but the total road distance travelled in these regions is rising at a much faster rate (about four per cent per year in the U.S.A.).There is also an explosive rise in car traffic in some countries, for example, by the year 20 10, the number of cars in China is predicted to grow 90-fold compared to the year 1990; while in India, the growth is expected to be 35-fold for the same period. Overall, the world car population could double from 400 million to 800 million in the next 20 years (1). How can the detrimental effects to the atmosphere of such rapid growth in road traffic be minimised? The regulated emissions, produced by road vehicles, of carbon monoxide, hydrocarbons and nitrogen oxides, are responsible for localised pollution problems, such as poor air quality or photochemical smog. T h e major unregulated emission, carbon dioxide, contributes to the global greenhouse effect, which is implicated in climate change. In recent years, vehicle manufactures have fitted a catalytic converter into the car exhaust system to reduce localised pollution. Current noble metal containing catalytic converters are very effective at removing 90 to 95 per cent of the regulated
L
Fig. 1 An 8-unit HotSpot”’ processor has a volume of 6 litres, weighs 8.8 kilograms and will produce 6000 litres per hour of hydrogen. Initially, the processor can be started by partial oxidation; after 25 seconds, heat is transferred from the reactors to the manifold; then after 100 seconds, the feed composition is changed to
allow steam reforming as well as partial oxidation
emissions, and are continuously being improved (2). The release of carbon dioxide is being tackled by edging-up vehicle efficiency from its present level of about 12 to 15 per cent, by improving the designs of the internal combustion engine and the vehicle structure. However, alternative technology, based on an electric motor powered by a fuel cell, is also being developed. The fuel cell offers the promise of vehicle efficiencies as high as 30 to 40 per cent, with no release of emissions other than pure steam. The high intrinsic efficiency of a fuel cell arises from the fact that, as an electrochemical reactor, it produces mainly electrical energy while converting hydrogen and oxygen to steam (3). By contrast, an internal combustion engine generates mostly waste heat and only a small proportion of useful mechanical energy. Furthermore, internal combustion of gasoline or diesel fuel produces a complex mixture of products, including unreacted hydrocarbons, carbon monoxide (from the incomplete combustion of the fuel) and nitrogen oxides. The major operational disadvantages of a fuel cell - its slow start-up and lack of response to short peak-loads - can be overcome by coupling it with a battery. Although the maximum efficiency is reduced to 25 to 35 per cent by this kind of hybridisation ( l ) , it is still substantially
Platinum Metals Rev., 1998, 42,(1)
higher than for a conventional internal combustion car. In the past year both Toyota and Daimler Benz have exhibited experimental passenger cars, in which electrical power is generated by a solid polymer fuel cell (SPFC). The Daimler Benz (Mercedes A-class) car is powered entirely by the SPFC, while the Toyota (Rav 4) car uses a fuel cellibatteryhybrid. Both cars carry methanol as fuel, which is catalytically processed on-board to produce a hydrogen-rich feed for the fuel cell.
On-Board Hydrogen Generation The concept of generating hydrogen while driving is widely seen as the answer to the supply problem caused by the absence of a ‘hydrogen economy’. However, the optimum choice of fuel and processor for this purpose is much more contentious. Daimler Benz and Toyota have demonstrated a commitment to using methanol and converting it to hydrogen by reaction with water (steam reforming). Other car companies would prefer to use existing motor fuels. With this aim, Arthur D. Little has recently demonstrated a compact fuel cell system, which produces hydrogen by reacting gasoline with a controlled amount of air (partial oxidation). In fact, most of the fuel-processing technologies being looked at or developed for mobile use
3
are based either on partial oxidation or steam reforming. Partial oxidation is a fast process, resulting in small reactor size, fast start-up and rapid response to changes in load. Being exothermic, however, it can lead to low vehicle efficiency ifthe heat generated is wasted. By contrast, steam reforming is potentially more efficient, producing hydrogen from both the fuel and the water feed. Being endothermic, ‘waste’ energy from other parts of the system can be usefully recycled. Unfortunately, steam reforming is a slow process, requiring a large reactor and long response times. Thus, to achieve compactness and fast response requires compromise. Usually methanol conversion, and hence efficiency, is sacrificed in an on-board steam reformer. The HotSpotTMreactor is a fitting alternative, as it combines the best features of both processing methods. It can be started up from cold by partial oxidation, so generating enough heat to drive the endothermic steam reforming process. Since both processes occur on the same HotSpotTMcatalyst particles, heat transfer occurs over microscopic distances, so avoiding the need for complex heat-exchange engineering. When surplus energy becomes available from other parts of the system (for example hydrogen rejected by the fuel cell) it can be diverted to the HotSpotrMreactor(s) to increase the amount of steam reforming. The reactors can be combined in parallel to produce a range of modular fuel processors with different maximum outputs, but identical response times. The relatively low concentration of carbon monoxide produced is removed catalytically by a small custom built reactor.
The History of HotSpotTM The original HotSpotTMreactor was invented in the mid 1980s (4). An oxygenate or a hydrocarbon was co-injected with air into a large bed of catalyst to produce a high yield of hydrogen ( 5 ) . The name ‘HotSpotTM’refers to the small reaction sphere (- I cm diameter) which formed around the point of injection, and in which most of the catalytic chemistry appeared to take place. When methanol was the processed fuel, the catalyst bed was prepared in two layers: the first
Platinum Metals Rev., 1998, 42,(1)
was a base metal partial oxidation catalyst; the second a noble metal total oxidation catalyst. The injection poiri was at the centre of the first layer. When methanol and air were injected into the cold reactor, total oxidation (to carbon dioxide and steam) began spontaneously as the reactants reached the lower layer. Transfer of heat back to the first layer initiated partial oxidation (to carbon dioxide and hydrogen) around the injection point and a hot spot began to form. A steady state (characterised by stable product composition) was reached after about 25 to 30 minutes. Thereafter, the temperature within the hot spot was stable at around 600°C. In this steady state there was complete conversion of methanol by partial oxidation, to produce 2 molecules of H?for each molecule of CH,OH consumed (6). The process was entirely self-sustaining. The reactor produced up to 12 times its own volume of hydrogen per hour. Although work has been done with hydrocarbon fuels, priority is presently being given to developing HotSpotTMfor on-board methanol processing, as we subscribe to the view, held in particular by the major German car manufacturers, that methanol merits careful consideration as a fuel for SPFC powered vehicles. This view comes from the facts that methanol: contains a high HIC ratio is a relatively clean fuel, both in terms of its production and composition, and can be made from renewable sources, and so need not add to the net carbon dioxide in the atmosphere. Through an iterative process of reactor engineering, catalyst design and performance mapping, the performance of the HotSpotTMreactor has been dramatically improved for methanol processing. The reactor now contains a singlebed of multicomponent noble metalhase metal catalyst. It produces hydrogen as soon as a feed of methanol/air or methanol/water/air enters, and it can reach steady state within a minute. T h e output has been improved by over two orders of magnitude, so that the current reactor produces 50 times its own volume of hydrogen per minute. Over the past 18 months, the design and construction of large HotSpotTM
4
methanol processors for integration into SPFC systems has been undertaken, with the development of other key components, such as a clean-up unit (to remove carbon monoxide) and a catalytic afterburner (to use the hydrogen rejected by the fuel cell) being part of the work.
The HotSpoiMMethanol Processor The current HotSpotTMreactor operates most efficiently when it converts methanol by a combination of (exothermic) partial oxidation and (endothermic) steam reforming. By supplying a feed of methanol/water/air, the two processes can be made to sustain each other. Under these autothermal conditions, as much as 2.4 moles H2are produced for each mole of CH,OH consumed. Also, the maximum temperature inside the reactor is only 400°C, giving excellent catalyst durability. If very low rates of hydrogen production are required, the methanol and water can be supplied as droplets or spray, while, for the high rates needed for vehicle applications, the liquid feeds should be vaporised. When a feed of steam, vaporised methanol and air (in the proportions needed for autothermal operation) is supplied to a cold reactor, hydrogen starts to form immediately and stabilises after several minutes. As shown in Figure 2, start-up can be accelerated by adding more air to the feed at first to promote partial oxidation. When the catalyst bed temperature approaches its optimum (after 40 seconds, see Figure 2(i)), the amount of air can be cutback, and the reactor rapidly reaches a steady state. Once there, any change in feed rate produces an instant change in hydrogen output. With the present design of processor, the maximum hydrogen output is 750 litres per hour, from a 245 cm’ reactor. This is equivalent to a power density of 3 kW per litre for each reactor, assuming that 1000 litres of hydrogen per hour will produce 1 kW of SPFC power.
Eliminating Carbon Monoxide In common with other fuel processors, the HotSpotTMmethanol reactor produces some carbon monoxide (CO). But, unlike some other technologies, it does not produce large spikes
Platinum Metals Rev., 1998,42, (1)
600
r, I--
$
400
! i ;
20c
I.
TIME, 5
Fig. 2 Start up of a HotSpotmmethanol reactor. Methanol vapour, steam and air are introduced into a cold reactor at feed rates selected to produce 625 litres of hydrogen per hour at steady state: (i) with 20 per cent extra air for accelerated start up: (ii) without extra air
of CO at any stage during normal operation. In fact, the rate of CO production by HotSpotTM is highly dependent on the catalyst bed temperature. In practice, this means that the product gas contains negligible C O during the first few seconds of start-up from cold. As the reactor approaches steady state, the CO concentration rises and stabilises at about 2 per cent. Carbon monoxide is a poison for SPFC at concentrations above about 40 ppm, therefore, it is necessary to remove most of the C O from the processed gas stream. O n assessing the usual removal methods, each was found lacking: catalytic methanation (reaction with hydrogen to form methane) - at best it consumes 3 molecules of useful hydrogen for each molecule of C O it removes, and at worst it can waste all the hydrogen if it converts the carbon dioxide in the processed gas as well; catalytic preferential oxidation - like methanation it is difficult to ensure that very little hydrogen is wasted; palladium (or palladium alloy) diffusers they require a high pressure differential and high temperature, both of which can impact badly on the overall efficiency of the system.
5
In view of these limitations, we have developed an advanced clean-up reactor, comprising several catalytic stages. Initially, we demonstrated, on a microreactor scale, that C O can be more effectively removed by a succession of small but highly selective stages, rather than by one large bed containing either a methanation or a preferential oxidation catalyst. The clean-up reactor has now been scaled-up to cope with the output from our largest current HotSpotTMprocessor (18 kW). The scaled-up reactor, which is less than half the size of the processor, reduces the C O concentration from > 2 per cent to < 10 ppm at the expense of 6 per cent of the hydrogen output. Based on kinetic studies of the underlying reaction rates, and on reactor simulations, it is thought possible to ultimately construct a clean-up reactor 20 per cent of the processor size which will allow 99 per cent of the hydrogen to pass through unreacted.
System Integration Apart from its intrinsic design, HotSpotTMis also distinguished by its modularity. Output is scaled-up by feeding the required number of individual reactors from a common manifold. For example, in Figure 1, a 6 kW methanol processor has 8 HotSpotTMreactors fed in parallel from a central manifold block. The reactors are connected to the block by inlet and outlet connections in the base of each reactor. Liquid methanol and water are sprayed at the required feed rates, using liquid-fuel injectors, into a central chamber inside the manifold, where they mix with a regulated flow of air. The manifold is maintained at 15O"C, ensuring the complete vaporisation of the liquid feeds. From the central chamber, the reactant mixture of methanol vapour, steam and air divides and travels an identical distance to each of the reactors. As a result, all the reactors and the complete processor have identical response to changes in input. The processed gas streams emerging from each reactor enter a common channel, which leads to a single exit port from the manifold. In the first few methanol processors that were constructed, the temperature of the manifolds could be raised to 150°C, by electrical cartridge
Platirrum Metals Rev., 1998, 42, ( 1 )
heaters, before the reactant feeds were introduced. The use of electrical heating during startup remains an option, as some battery power will be available on all SPFC vehicles. However, as electrical power will be required by several components (such as pumps, compressors, electronic controls, lights) when the vehicle is started from cold, other options for heating the manifold would lessen the load. One strategy is to generate heat internally, by first carrying out mainly partial oxidation in the HotSpot'Mreactors. As the hot processed gas emerges from the reactors it transfers heat to the manifold. Once the manifold has reached 150°C, the water feed can be switched on, the methano1:air ratio can be altered to induce steam reforming as well as partial oxidation, and the feed rates can be increased. Another start-up approach is to combust methanol in a separated catalytic afterburner, with the resulting heat being transferred to the manifold. In one processing system currently being tested, hot exhaust gas from the afterburner is circulated within the manifold through a long internal loop. One drawback of using processed gas, instead of neat hydrogen, to feed a fuel cell is that some of the hydrogen will emerge unreacted. Typically, a fuel cell rejects 20 to 30 per cent of the hydrogen in a processed gas stream. This need not have a substantial impact on efficiency, ifthe energy contained within the rejected hydrogen can be usefully recycled. HotSpot"" provides a very effective sink for this energy. By combusting the hydrogen, the heat produced can be transferred to the manifold and hence to the reactants, so encouraging more steam reforming. In effect, this allows more water to be converted to hydrogen. T o simplify the system design, a noble metal catalyst which allows the same afterburner to be used for combusting both hydrogen and methanol has been developed, see Figure 3. The catalyst is so active that light-off begins as soon as cold methanol is sprayed into an air stream entering the afterburner. When rejected hydrogen becomes available, it can be fed to the afterburner in place of the methanol. This afterburner, therefore, not only enables fast start-up,
6
Fig. 3 Here, the manifold i s heated by energy generated externally, either by heat supplied by the combustion of methanol in the afterburner during a cold start, or by heat supplied by the combustion of surplus hydrogen in the afterburner during steady state nperation
improved integration of the components. The question of whether methanol is the correct fuel for SPFC vehicles does not have a simple answer. Methanol is highly suited for onboard processing, but hydrocarbons have the Future Prospects The hydrogen output from a single HotSpotTM advantage, being the established vehicle fuels methanol reactor results in a very high power with a global infrastructure for their supply and density (3 kW per litre). This drops to just over distribution. We are sure, though, that HotSpotTM 1 kW per litre for a modular processor, because is the right processing technology. From our of the spacing between reactors and the extra work on methanol, we know that HotSpotTMcan volume required by the manifold. As the proces- match the efficiency of steam reforming and can sor must be coupled with a clean-up reactor substantially exceed that of partial oxidation. In to eliminate carbon monoxide, the power den- its speed of start-up and rate of response to sity is reduced further to 0.75 kW per litre. This changes in load, HotSpotTMmatches partial value already meets the target for fuel proces- oxidation and outperforms steam reforming. The fuel debate is unlikely to be resolved soon; sors that has been adopted by U.S. car manufacturers (7); and yet, HotSpotThl is far from so we are preparing for the possibility that SPFCoptimised. In the immediate future, the design vehicle manufacturers will offer more than one and performance of the HotSpotTMprocessor choice of fuel, probably between methanol and will be improved by: a more conventional vehicle fuel. In the meantime, research and development of HotSpotTM increased output from individual reactors technology will continue, aimed at achieving an reduced manifold size ideal methanol processing system and a novel reduced size of the clean-up reactor increased selectivity in the clean-up reactor hydrocarbon processor. but also increases the steady-state operating efficiency, and ensures that only carbon dioxide and water are released into the atmosphere.
References R. Q. Riley, “Alternative Cars in the 21st Century”, SAE, Warrendale, U.S.A., 1994 2 S. T. Gulati et al, “Advanced Three-Way Converter System for High Temperature Exhaust Aftertreatement”, SAE 970265, 1997 3 T. R. Ralph, Platinum Metals Rev., 1997,41, (3), 102 1
Plarirricrir hlcruls Rev., 1998, 42, (1)
4 J. W. Jenkins, European Pazenz 217,532, 1987 5 J. W. Jenkins, European Patent 262,947, 1988 6 J. W. Jenkins and E. Shun, Platinum Metals Rev., 1989,33, (3), 1 18 7 “Reviewof the Research Program of the Partnership for a New Generation of Vehicles”,Third Report, National Academy Press, Washington DC, 1997
7
Acoustic Wave Enhancement of Catalytic Reaction Rates over Platinum Surfaces By Sven Kelling and David A. King Department of Chemistry, University of Cambridge, England Sonochemistry has been deployed in liquid and liquid-solid systems in recent years to generate rapid reaction rates and diverse chemical products (1). T h e underlying mechanism is based on acoustically-induced cavitation in the liquid phase, and is therefore not applicable in the gas phase - at least at low pressures. However, about five years ago Inoue and Matsukawa first reported remarkable increases in the rates of catalytic reactions at the gas-solid interface by exciting acoustic waves across the catalyst surface (2). These early studies, recently reviewed ( 3 ) , were performed in a gas circulating apparatus operating at around 30 Torr with polycrystalline films as catalysts. Several important questions were raised by this work: 8 Since significant acoustic power was dissipated at the metal surface, was the effect simply attributable to an increase in the surface temperature of the catalyst? a At the pressures used in these experiments, reactant transport through the gas phase can become rate determining: is the effect attributable to acoustic-wave-induced mixing in the gas phase above the catalyst? a Finally, if the effect could be attributable to a non-thermal surface process, what is the physical nature of this process?
This last question is intriguing, since the quantum of energy associated with acoustic waves in the range used (- 10' Hz) is about 10' times smaller than the barrier associated with a surface reaction. Our approach was to tackle each of these questions in turn, using well characterised platinum single crystals in an ultrahigh-vacuumcompatible excitation system, with a base pressure of 2 x 10 '" Torr. Acoustic waves were excited across a 500 nm x 10 mm x 10 m m Pt{ 1 l o } crystal, and detected by an interdigital transducer (IDT) (3). The platinum crystal was grown on a suitable cut, polished and irradiated NaCl substrate and floated away from it in water, before cold-welding it onto a polcd Y-cut LiNbO, single crystal substrate with both input and output aluminium IDTs, as shown in Figure 1. The system operates by exciting Rayleigh waves in the frequency range 19 to 20 MHz. A tunable ultrahigh amplitude and frequency resolution vector-analyser spectrometer were used both for excitation and to detect the acoustic signal transmitted across the platinum crystal surface (4). The RF power generated across the crystal during the experiments described here is of the order of 1 watt. A novel method had to be developed to
Fig. 1 The device u w d t o cxcitc. surface ucountic. waves (SAW) ronsists of t w o ititrrdigitul transducer electrode arruys with u thin film singlc crystnl sntiiple cold welded in-hetween
Platinum Metals Rev., 1998, 42, (l), 8-10
8
Fig. 2 Carbon monoxide partial pressure depeudenee of the reaction rate enhancement on acoustic wave excitation measured at a sample temperature of 528 K at a constant oxygen pressure of 1.2 x lo-' Torr. 100 per cent CO pressure equals 1.2 x Torr
4
k
'23 w-
5
2 K
2
2
20
60
40
PERCENTAGE co (100.1.
measure accurately the temperature of the metal crystal both before and after acoustic excitation. The method is based on the remarkable thermal sensitivity of the frequency at which resonance peaks occur in the acoustic spectrum. We found shifts in the region of 2 kHz per degree temperature change, which could be detected with high accuracy using our acoustic spectrometer (5). Experiments could be conducted under accurately isothermal conditions. As a test reaction we chose CO oxidation with 02, and the experiments demonstrated unequivocal evidence for a non-thermal enhancement
100
80
= 1.2x lo-' Torr)
of the reaction rate at relatively low partial pressures of the reactants. T h e magnitude of the enhancement factor was between 1 and 4, depending on partial pressures (6). At these pressures gaseous flow is strictly molecular (there are negligible numbers of molecule-molecule collisions in the gas phase) and this result therefore also demonstrates that, at least under these conditions, this is a surface effect not attributable to acoustic-wave-induced mixing in the gas phase. Interestingly, it was also found that the effect was not dependent on the acoustic wave frequency; in particular it was not attributable
SAMPLE TEMPERATURE, K
345
395
445
495
545
2.5
$1.5-
Fig. 3 The temperature dependence of the aaoustie effect between 340 and 545 K sample temperature for a constant O1 pressure of 1.2 x Torr and CO pressure of 3.2 x lo-' Torr. Temperature (top axis) was ealculated from the position of a resonance peak in the acoustic spectrum (main x-axis)
Platinum Metals Rev., 1998, 42, (1)
m 3 W
a 1 0J
I! K
0.50
I
II +without I
19.30
I
I
19.25
19.20
acoustic excitation
I
I
I
19.15
19.10
CENTRE FREOUENCY MHL
9
to acoustic wave resonances observed in the acoustic wave spectra, as had been suggested by Boronin and co-workers (7). Results were compared with and without acoustic wave excitation over a wide range of crystal temperatures and CO partial pressures, at fixed 0,partial pressure (6). From the results, samples ofwhich are shown in Figures 2 and 3, the following observations were made. There was no acoustic excitation at low C O pressures (high OcCO ratios), but as the CO pressure was raised the rate of COr production was found to be shifted towards a lower 0 2 : C 0ratio with the acoustic wave excitation on. Similarly the temperature dependence of the reaction rate at constant 0,:CO ratio showed that a given reaction rate was reached at a h e r temperature with the acoustic wave switched on. From Arrhenius plots, however, it was shown that the overall activation energy for the process was unaffected by acoustic wave excitation. In further exploratory experiments we found, first, that acoustic wave excitation had no detectable influence on the clean surface Pt(1 lo} (1 x 2) LEED pattern, although microscopic examination of samples after extensive excitation did reveal significant morphological changes. Secondly, using Reflection Absorption Infrared Spectroscopywe could detect no change in the CO absorption band from chemisorbed CO on the Pt { 1 10) surface due to acoustic excitation; in particular, n o site switching was induced. More work, both theoretical and experimental, is required to understand the physical mechanism underlying the process. In order to examine the mesoscopic-scale distribution of adsorbate on the surface, and its possible alteration by acoustic waves, we are currently undertaking experiments with Rotermund in Berlin using a Photoelectron Emission Microscope: the coupling of low frequency, long wavelength vibrational modes into the reactive behaviour of adsorbates must presumably involve mesoscopic-scale substructures on the surface, and we hope to find direct evidence for this. In the meantime, Inoue and his group at Nagaoka in Japan have reported some very large catalytic
Platinum Metals Rev., 1998, 42, (1)
enhancement factors in catalytic processes at relatively high pressures (8) and, whatever the mechanism, the technological potential in the use of acoustic waves across catalyst beds deserves attention. References K. S. Suslick, Science, 1990, 247, 1439 Y . Inoue and Y . Matsukawa, Chem. Phys. Lett., 1992,198,246
M. Gruyters, T. Mitrelias and D. A. King, Appl. Phys. A, 1995,61,243 T. Mitrelias, V. P. Ostanin, M. Gruyters and D. A. King, Appl. Surf: Sci., 1996, 101, 105 S. Kelling, T. Mitrelias, Y . Matsumoto, V. P. Ostanin and D. A. King,J.C.S. Faraday Discuss., in press S. Kelling, T. Mitrelias, Y . Matsumoto, V. P. Ostanin and D. A. King, 3. Chem. Phys., 1997, 107,5609
V. N. Brezhnev, A. I. Boronin, V. P. Ostanin, V. S. Tupikov and A. N. Belyaev, Chem. Phys. Lett., 1992, 191, 379
Y . Inoue, Y . Watanabe and T. Noguchi,J. Phys. Chem., 1995,99,9898
Cold Platinum Cathode Field emission displays which use cold cathodes to generate the electron beam are highly suitable for future flat panel displays as they provide complete colour capability, have a large viewing angle and are cost efficient. But until now, cold cathodes have produced an electron emission efficiency of less that one per cent. Now, however, a team fi-om Pioneer Electronic Corporation, Japan, has developed a cold cathode with a greatly increased electron emission efficiency using a Pt/SiOdSi/Al structure on a thermally oxidised silicon substrate (N.Negishi, T. Chuman, S. Iwasaki, T. Yoshikawa, H. Ito and K. Ogasawara,Jpn. J. Appl. Phys., Part 2, 1997, 36, (7B),L939-L941). The silica and silicon films, 400 nm and 5 km thick, respectively, and platinum, 10 nm thick, were deposited onto a 300 nm thick film of aluminium, with the platinum and aluminum films used as the cathode electrodes. T h e electron emission was evaluated using a glass plate coated with a transparent electrode of indium-tin oxide and phosphors as anode and screen, respectively. At room temperature and with an applied voltage of 110 V and accelerating voltage of 5 kV, an electron emission efficiency of 28 per cent was achieved together with brightness for green emission of 80 kcd m ', using ZnS:Cu,Al. The high emission efficiency may be closely linked to the occurrence of negative resistance.
10
The Development of Platino-Calixarenes TRAPPING PLATINUM HYDRIDES IN MOLECULAR CAVITIES
By Catherine Wieser-Jeunesse and Dominique Matt UniversitC Louis Pasteur, Groupe de Chimie Inorganique MoMculak, Strasbourg, France
Although many promising aspects of the chemistryof calixldjarenes have been highlighted in recent years, relatively little attention has been paid to the coordination chemistry of these m(lcT0cYclie moleeule9. Thepresew paper describes some recent developments made with platinum metal complexes attached to calk phosphine ligands, that is, calixurenes substituted withphosphinogroups. Hydrido complexes, especially of the platinum group metals, have a pivotal role in homogeneous catalysis (1). They appear as intermediates in many catalytic cycles, including hydroformylation, asymmetric hydrogenation, hydroxycarboxylation, and oligomerisation of olefins. In order to perform highly selective hydrido-mediated catalytic reactions it is essential that ligands are present which allow both fine-tuning of the M-H bond reactivity and proper discrimination of incoming substrates, with thc latter being especially important for enantioselectivity.A major limitation of presently available platinum metal hydride catalysts concerns the freely accessible reactive metal centre. With such species, there is no easy way to discriminate between incoming substrates of different shape. A difficult challenge to be overcome during the development of the next generation of hydride catalysts is to locate the platinum metal hydrides inside well-defined
I
Scheme I A molecnlar cavity Functiening a8 o shape selecting recognition unit
Platinum Metals Rev., 1998,42,(l), 11-16
molecular pockets. Such structures are expected to possess valuable properties, in particular with respect to shape-selectivereactions, that is, where the cavity functions as a molecular recognition unit by which to channel the substrate to the catalytic site in a preferred orientation, see Scheme I. Possible synthons for the construction of appropriate molecular cavities are the calix [4]arenes, but there has been little success in combining them with reactive metallo-fragments. Calix[4]arenes (L) constitute a class of versatile building blocks that have recently become very useful in the general area of molecular engineering (2). They are cone-shaped macrocyclic compounds comprising four phenolic units linked together in a circular array by methylene bridges connected at the ortho positions of the phenolic rings. An essential feature is the presence of phenoxy rings oriented in the same direction, so that, in principle, tethering of functional groups either to the phenolic oxygen atoms or to the pcarbon atoms generates well-organised cavities which may provide attractive binding zones for incoming ionic or neutral species. Thus, for instance, the p-derivatised calixarene L’, see Scheme 11, in which the cone shape is retained, displays remarkable complexing properties towards actinides, with a binding affinity being some 200-fold better than that of the monomeric counterparts, namely the 0,O-chelators, formula R,P(0)CH2C(O)NRR (3). For other calix[4]arenes showing receptor properties, attachment to the calixarene platform of
11
,opy 9 H H
H
Php
Ph2
U"
-T
Pp
H
0
!f
'fY
L
L'
9 y
'f = C10H21
L'
Scheme I1 Multifunctional ligands built on a calix[4]arene platform
specific additional substituents which contain redox-responsive functionalities - for example a ferrocenyl group as in L' - may provide novel potentiometric sensors suitable for the selective detection of various anionic substrates (4).
Strapping a Metal Centre across the Mouth of a Calix[P]arene The so-called metallocalixarenes are of particular interest; they form a novel class of complexes having a transition metal centre closely
Plutitiuvrr Metals Rev., 1998, 42, (1)
connected to one mouth of a calixarene. In such compounds several functional groups attached to the calix platform may simultaneously approach the metal atom in a convergent way. They form a protective layer around part of the metallo-fragment that helps in the control of the electronic and redox properties. Examples of compounds in which a metal centre sits at the entrance of a calixarene tunnel are shown in Scheme 111. All the complexes in Scheme I11 were formed from calix[4] arenes bearing two
12
phosphine ligands bound to two distal (or opposite) phenolic units. The auxiliary functions that are attached to the other two phenolic rings ensure the confinement of the metal inside the pocket. The net result is to provide an artificial redox-active enzyme. Phosphino groups were chosen as primary co-ordination sites, because of their ability to form complexes with all transition metals, and their importance to homogeneous catalysis. The auxiliary side-arms are key elements for controlling the solubility, charge, polarity and stereochemistry of the whole complex. Synthetic methodology for capping a calixarene with a metallo-fragment has been recently developed in our laboratory and is illustrated in Scheme IV (5). The reaction of the mixed etherphosphine L ' in refluxing tetrahydrofuran (THF) afforded platinum complex 1, in 100 per cent yield. The formation of this large metallo-macrocycle (containing two contiguous 16-membered metallo-rings) which occurs quantitatively, regardless of the metal concentration, demonstrates that the macrocycle behaves here as an effective template that allows the diphosphine to function as a chelator.
Platiitunr Metuls Rev., 1998, 42, (1)
Replacement of the auxiliary ether groups by other substituents may change the course of the reaction considerably. Thus, if calixarenes with side-chains which possess higher-binding af€inities than ethers are used (such as the amide calixarene L') then both of the triphenylphosphine ligands will be replaced and a neutral hydridochloro complex will be formed. T h e two amide groups of L4probably behave as internal solvent molecules, giving rise to the formation of transient penta co-ordinated platinum species which rearrange by successive loss of the triphenylphosphine ligands. A related neighbouring group effect which can promote ligand displacement, sometimes referred to as anchimeric assistance, was also found to operate when the side chains contain ester groups (6).
Entrapment of Platinum Hydrides within a Cavity An interesting aspect of the structure of complex 2 is the localisation and orientation of the platinum-hydrogen bond. Two-dimensional rotating h e Overhauserspectroscopy(ROESY) experiments unambiguously demonstrate that the hydride, which resonates at -1 5.04 ppm
13
Fig. 1 The moleeular structure of complex 2. The t-butyl groups of the ealixarene and the phenyl rings of the phosphorus atoms have been omitted for clarity.
Dihedral angles between the opposite aryl rings of the calixarene matrix: 80.1(4) and 14(1)”
&I,,
= 1 150 Hz, ‘JIJI’-H = 15 Hz), is close to the
C H 2groups of the four pendant arms and also to the axial H atoms on the bridging methylene groups of the calixarene. In other words, the Pt + H vector must point towards the centre of the calixarene cavity. The results of an X-ray structural investigation, see Figure 1, confirms our conclusion drawn from studies of the solution, and shows that the hydride is trapped inside the cavity formed by the substituents. In view of the important crowding that takes place around the platinum-hydrogen bond it is not surprising to find that this bond displays high stability towards potential reagents, such as ethene or MeO2CC=CCO2Me,which normally insert into the platinum-hydrogen bond, when it is not sterically protected. Smaller reagents would probably be able to enter the calixarene through the opposite end. If this happens it would result in a reaction taking place inside the cavity, but this goal has not yet been reached. Figure 1 also illustrates the flexibility of the calixarene matrix which adopts a deformed “cone” shape with two phenoxy rings facing each other and the other two lying almost perpendicular. Such a flattened geometry is frequently encountered in calixarenes in the so-called cone conformation (7). Under forcing conditions, and again with the help of a neighbouring amide group, the direction of the Pt-H bond can be modified. Thus, the reaction of complex 2 with silver tetrafluo-
Plarbsutir Merals Rev., 1998, 42, (1)
roborate yields the hydrido complex 3,see Figure 2, where the Pt-H bond now points to the exterior of the cavity. In this arrangement, the hydride becomes much more reactive and
3
L*
4
Fig. 2 The molecular structures of the platinun) complex 3, the chiral diphosphine ligand L and the rhodium complex 4
14
participates in insertion reactions with added substrates (vide infru). A consequence of the P,P,O-tridentate behaviour of the ligand is that the cavity caps the platinum plane in a way that makes the regions above and below the metal plane asymmetric. It might be anticipated that structures where a cavity surrounds a co-ordination site would favour activation by the metal of those substrates which possess a shape compatible with the size of the molecular pocket. Furthermore, reactive intermediates formed inside the cavity might be stabilised in such a way as to direct subsequent reactions towards the desired products. We expect to exploit this structural sensitivity of the emerging transition state to optimise catalytic processes such as ethene polymerisation or ethene/CO co-polymerisation. Structurally-related complexes can also be obtained with rhodium; thus rhodium complex 4 was obtained from the chiral diphosphine L’, see Figure 2, so as to place the metal in a chiral pocket. An interesting synthetic methodology for reinserting the hydride inside the molecular pocket
Platinum Metals Rev., 1998, 42, (1)
was found when complex 3 was treated with donors that displace the co-ordinated amide group. This strategy not only allows us to vary the electronic properties of the encapsulated hydride, but it also provides access to large assemblies, such as the bimetallic hydrido complex 5, obtained by reacting L4with 4,4’-bipyridine, see Scheme V. In contrast to the encapsulated hydrido complexes which are relatively inert, the “open” hydride 3 reacts readily with electrophilic species resulting in the formation of insertion products. Thus, with dimethylacetylene dicarboxylate (MeOrCC=CCOrMe),complex 3 converts into the platinum alkenyl complex 6. In this complex the high rruns influence of the so-formed platinum-carbon bond labilises the co-ordinated amide group and favours substitution at the free co-ordination site by the second amide group. Amide exchange is likely to occur via formation of penta co-ordinated platinum (11) species. This leads to the pendular motion depicted in Scheme VI. Using a simplified description, this cationic complex can be regarded as containing
15
a metal centre with a free co-ordination site that remains entrapped inside a cavity and which flips from one amide to the other.
Future Opportunities Potential applications of platino-calixarenes are in the field of homogeneous catalysis. The localisation of reactive organometallic fragments inside molecular pockets is primarily expected to favour shape selectivity and promote enantioselectivity, when the pocket is chiral. A possible extension concerns the development of two-phase catalysts based on cavities substituted with water-solubilising groups located at their periphery. If the interior of the cavity is sufficiently lipophilic, highly efficient phase-transfer catalysis could be achieved. Clearly the dimension of the cavity must be adapted to the size of the substrate. This can be done if one considers that larger calixarenes are now readily accessible. The fact that calixarene matrices offer many opportunities for functionalisation - the aromatic pcarbon atoms of the phenol rings may also be functionalised opens the way for further possible objectives, such as the preparation of immobilised systems suitable for solid state reactions or, provided that the systems contain additional electro- or photo-active functionalities, their use as specific sensors.
Acknowledgements The authors wish to warmly thank Prof. A. Harriman for many interesting discussions about this topic. We would also like to thank Johnson Matthey PLC for a generous loan of platinum metals.
Platinum Metals Rev., 1998, 42, (1)
References F. H. Jardine, in “Chemistry of the Platinum Group Metals”, ed. F. R. Hartley, Elsevier, New York, 1991, Chapter 13 2 C. D. Gutsche, “Monographs in Supramolecular Chemistry”,Vol. 1: Calkarenes, ed. J. F. Stoddart, The Royal Society of Chemistry, London, 1989 3 F. Arnaud-Neu, V. Bohmer, J.-F. Dozol, C. Griittner, R. A. Jakobi, D. Kraft, 0. Mauprivez, H. Rouquette, M.-J. Schwing-Weill, N. Simon and W. Vogt,3. Chem. SOC.,Perkin Tram. 2, 1996, 1
1175
P. D. Beer, Z. Chen, A. J. Goulden, A. Graydon, S. E. Stokes and T. Wear,J. Chem. Sac., Chem. Commun., 1993, 1834 5 C. Wieser, D. Matt, J. Fischer and A. Harriman, J . Chem. SOC.,Dalton Trans., 1997, 2391; C. Wieser, C. Dieleman and D. Matt, Coord. Chem. Rev., 1997, 165, 93; C. Wieser, D. Matt, L. Toupet, H. Bourgeois and J.-P. Kintzinger, J. Chem. SOC.,Dalton Trans., 1996,4041 6 E. M. Miller and B. L. Shaw,J. Chem. SOC., Dalton Trans., 1973, 480 7 C. Dieleman, D. Matt and P. G . Jones, J. Organomet. Chem., 1 9 9 7 , 5 4 5 5 4 6 , 4 6 1
4
Catalytic Reaction Guide Johnson Matthey has recently updated and re-issued its popular “Catalytic Reaction Guide”. In the form of a pocket-sized slide chart, catalyst recommendations, with typical operating conditions are given for 69 key chemical reactions of industrial significance. Over a quarter of the entries are homogeneously catalysed reactions, which acknowledges the increasing importance of this technology. Among specific reactions included are: hydrogenations, carbonylations, carbon-carbon couplings and selective oxidations. For further information, please contact Johnson Matthey by telephone: +44 (0) 1763 253000;Fax: +44 (0) 1763 253668; E-mail: CATENQBmatthey .corn. D. E. GROVE
16
Contemporary Platinum Chemistry Inorganica Chimica Acta: Special Volumes on Platinum Chemistry 1997, November, Volumes 264 and 265, Parts I and I1
As part of its policy of publishing themed volumes on selected topics, Znorgunicu Chimica Actu has devoted volumes 264 and 265 to platinum chemistry. These include 60 articles, plus communications and notes, giving effective coverage of the current state of platinum coordination chemistry research as reported by those most active in this field. The continuing interest in platinum-amine coordination chemistry resulting from the anticancer use of cisplatin is evident in several papers, including those by Clark, Buncel, Gust, Krebs and Gibson (Pt(I1) compounds}, Lippert {Pt(III)}and Beck and Keppler {Pt(IV)}.The possibility of combining the anti-tumour effects of platinum with photodynamic therapy is investigated by Brunner through the synthesis of platinum porphyrin conjugates. The acidity of water and ammonia bound to platinum(1V) plays an important role in the substitution chemistry of these complexes and a study of the deprotonation reactions of amido-ammineplatinum(IV) species is described by Frank. The syntheses and structures of bipyridyl platinum(1VIV) phenoxide complexes are reported by van Koten. Sulfoxide complexes of platinum form useful starting materials for many reactions. Fanizzi and Rochon discuss different aspects of the structure and reactivity of such compounds. The co-ordination and bonding of phosphorusdonor ligands continues to prove a rich field for study. The preparation and structure of the secondary phosphine complex [Pt(PBu',H),] is described by Leoni. The bonding of bidentate P-donor ligands is discussed in papers by Tanase and Roddick, co-ordination of tetradentate P A ligands is described by Reid and of multidentate P/N-donors is reported by Feringa. NMR has long been used to study the coordination of phosphorus-donor ligands to metals and this method has now been used by Pringle to examine the roles of 0-and rc-bonding in the co-ordination of these ligands in Pt(0)
Platinum Metals Rev., 1998, 42,( l ) , 17
and Pt(I1) complexes. The effect of the electronic and steric properties of phosphines on substitution of platinum (11) complexes is discussed by Romeo, while the bonding of a phosphite ligand to the cluster compound [Pt& C0),(p,-Ph,PCH2PPhJ3] is reported by Puddephatt. Oxidative addition reactions of this cluster are described in a further paper by Puddephatt. Many papers deal with the chemistry of multinuclear molecules. Aspects of the structure of homonuclear dimeric compounds are discussed by Cotton (metal-metal bonding) and by Venanzi and Fryzuk (hydrogen-bridged compounds) while the chemistry of a number of heteronuclear dimeric complexes is described by other authors. The application of NMR to the study of fluxional behaviour is illustrated by the work of Gonzalez-Duarte on dinuclear sulfurbridged complexes. The structures of other dinuclear sulfur-bridged platinum and palladium compounds are described by Albinati. A discussion of the influence of stereochemical and electronic factors leading to the formation of icosahedral clusters is given by Teo. The organometallic chemistry of platinum is represented by papers from Ogoshi, Casey (propargyl complexes), Jennings (metallacyclobutanes), Takahashi (carbene compounds) and Young (neopentyl derivatives) among others. The rearrangement of 5-co-ordinate platinum(I1) olefin complexes is discussed by Albano, while the stabilisation of otherwise unstable olefins by co-ordination in such complexes is described by Panunzi. Of necessity, when dealing with such a large number of articles, the papers highlighted here reflect the personal interests of the reviewer and each reader will no doubt find other papers to interest him or her. These volumes provide an interesting snapshot on current work on platinum chemistry with the emphasis on co-ordiC . F. J. BARNARD nation and structure.
17
New Studies in Fullerene Chemistry SOME RUSSIAN PLATINUM METALS FULLERENES RESEARCH
By Viatcheslav I. Sokolov and Vasily V. Bashilov Institute of Organoelement Compounds, Russian Acadrmy of Sc*irnc*rs. Moscow. Russia
Studies onfullerene chemistry carried out in the Laboratory of Organometallic Stereochemistry ai ZNEOS,Moscow, are briefly reported. These include work with platinum metals complexes, in particular, on novel methods of preparing fifdlerene (Gand C,) complexes ofplatinum, palladium, rhodium and iridium. A new appmach is the use of mercury-platinum bimetallic compounds, R-Hg-PtLyX, as a source of the PtL, moiety to be transferred onto a ( 6 5 ) double bond i n fullerenes. Bis(aryl)platinum( 11) complexes can react similarly Otherproducts of this reaction are discussed. Thefirst optically active organometallic fullerenes of the type C . M ( + ) DZOE where n = 60 or 70, have ulso been prepared and the circular dichroism spectra investigated. I n addirion, the molecular structuresfor CN,Pd(PPh,)? and C~.tPt(+)DIOPhave been solved. Higher catal-ytic activity for the hydrogenation ofu triple to u double bond has been observed with C,#,Pd(PPh,)l adsorbpd on porous carbon than with palladiumlporous carbon. The stability of the giant carbon cluster C,,,, was first predicted by quantum chemical calculations in the 1970s (1,2), but the actual existence of both C,,, and C7,,in carbon vapour was not discovered until 1985, when it was detected by mass spectrometry ( 3 ) , and resulted in the award of the Nobel Prize for Chemistry in 1996 to Curl, Kroto and Smalley. However, for chemical study, fullerenes only became available in multigram quantities five years later, after the development of the carbon arc burning method (4). The study of fullerenes is interdisciplinary, as they have relevance, for example, to: solid state physics, spectroscopy, chemistry, materials science, astrophysics, life sciences and geology. As chemical entities fullerenes are different from other forms of carbon, such as diamond, graphite, or linear carbon, in that they constitute a whole family of isolated individual molecules rather than a continuous polymeric system. From a chemical point of view, fullerenes can be regarded as highly unsaturated, strained alkenes, with an unusual three-dimensional structure, made exclusively of carbon, and as
Pl~tiirirtiiMetuls
Rev., 1998, 42, ( l ) , 18-24
such they have attracted a lot of attention in terms of their general reactivity - in particular as ligands for transition metals. This latter field of study was initiated by the work of Fagan, Calabrese and Malone who described the first platinum q2-bonded C,,, complex ( 5 ) . Shortly afterwards we reported that the structures of the fullerenes permit them, in principle, to act as ligands of different hapticity, continuously from q ' to 11"( 6 ) . One aspect that has been of great interest to us is that chirality may occur in doubly metallated exohedral complexes when the two metal groups are identical: in if,q"-C,,,,and in q",q"-C7,,,i1",q'-C7,tand q',~i'-C~,~ (7). Both pentahapto- and hexahaptometal complexes are well-known in platinum metals chemistry (as shown for instance, by metallocenes and arene-metal complexes). However, in fullerene chemistry, only q'-ligated metal complexes had been reported until 1996, when the synthesis of qi metal derivatives of X,C,.,) with a partly broken fullerene structure was reported (8). Recently, this Journal published a survey of some current results in the area of fullerenes
18
The Electrochemistryof Reductive wave potentials, - E,,z,,,d,,volts
Compound
I CmPd(PPh3)z CsoPd(PPh3)z + Pd(PPh3)a
0.34 0.34
I
I
0.78
I
I
1.30
I
1.78
0.57
0.78
0.99
1.27
1.47
0.57
0.81
0.99
1.25
1.48
bonded to the platinum group metals (9) in which one paper of the present authors was referred to. However, there is other work on this topic published by our group, which has largely gone unreported in the review literature (10). Therefore, we would like to take this opportunity of briefly outlining our results. Topics in fullerene chemistry in which we are interested include: (i) the synthesis, molecular structure and reactivity of C,, and C,, co-ordinated to the platinum group metals; (ii) the formation and reactivity of Z-fullerenyl free radicals, where group Z is linked to the fullerene through the magnetic nucleus (such as "P, 'OB-l'B, Iq5Pt,etc.) for study by ESR (electron spin resonance) spectroscopy; (iii) optically active organometallic fullerene derivatives.
I
2.30
This suggests that essential electron transfer occurs from the metal to the fullerene core. The X-ray structure of a related, optically active, platinum fullerene complex has also been solved (vide infra). An electrochemical study of q2-Cb0Pd(PPh& in acetonitrile in the presence of an excess of either Pd(PPh,), or PPh, revealed the disappearance of some reductive waves common to free C b O , see the Table, above (1 2). This was interpreted to mean the existence of the following equilibrium: 2 CJ'd(PPhi)2
ft
Cou[Pd(PPh,)i]2 + Cm
without phosphine ligand dissociation. We have found a novel, alternative method for the preparation of platinum fullerene complexes using mercury-platinum compounds of general formula R-Hg-PtL2-X as a source of the PtL2 moiety (13). The synthesis of this group of mercury-platinum organobimetallic compounds was Synthesis of Fullerenes with previously developed by us; it involves the inserPlatinum and Palladium T h e synthesis and molecular structures of tion of Pt(0) carbenoids into the mercury-elepalladium fullerene complexes have been ment bond (Hg-X), where the element X may reported by us (1 1). X-ray investigations have be halogen, carbon or a metal and R is an organyl revealed that distortions of the fullerene cores group (14). The important structural feature of in both platinum and palladium q2-C60M(PPh,)2 these organobimetallics is a ck-arrangement complexes are very similar (1 1). The most inter- of two phosphine ligands (L) around the platesting feature of these complexes is their square inum atom. The stability of these mercury-platplanar - rather than tetrahedral - arrangement inum compounds has been known to depend of four ligated atoms around the metal. This is strongly on the nature of groups R and X. It different from Pt(0) and Pd(0) complexes with was found that their reactivity, versus fdlerenes, normal alkenes, such as ethylene, but similar to may be different as a consequence. Thus, if only those with electron-withdrawing alkenes, such common groups, such as halogen, aryl or alkyl as tetrafluoroethylene or tetracyanoethylene. are present in the molecule, then Pt(PPh3)z is
Platinum Metals Rev., 1998, 42, (1)
19
hv
Ph2C=CH-Pt(PPh,)z-Hg-CF(CF,)z CH=CPhi
I
+ Csa + ESR spectrum
g
=
2 0013
hfs constants (gauss).
'Cso - Pt - PPh,
I
ar2
PPh,
30.5 35
Scheme I A olatinum hllerenvl radical
transferred smoothly onto a fullerenyl [ 6 : 6 ] with bis-organylplatinum complexes, Ar2PtLz, double bond. where Ar = ptolyl, again to give q'-C60Pt(PPh,)Z However, when R is the electron-withdrawand biaryls (16). The reaction appeared to proing perfluoroalkyl group, homolysis of the metal- ceed as a concerted process with initial co-ordimetal bond occurs selectively, leaving the plat- nation between the platinum atom and the inum-carbon bond intact. Initially a platinum- double bond. centred free radical is formed which immediately attaches to the fullerene to give a relatively sta- Formation and Reactivity of ble platinum fullerenyl radical, observable by Z-Fullerenyl Free Radicals Fullerenes themselves are known readily to ESR at room temperature (1 3), see Scheme I. Its structure is explained by the ESR spectrum, add many kinds of free radicals (1 7). We have where hyperfine splitting (hfs) is observed due studied the behaviour of q'-CouM(PPh,)2durto one platinum ('"'Pt) and two non-equiva- ing the reaction with free dialkoxyphosphoryl lent phosphorus ("P) nuclei. This shows that radicals, (AlkO),P(O)*. Several low intensity the cis-arrangement of the two phosphine lig- ESR signals were observed in addition to the parent *C,J'(0)(OAlk)z signal, which indicates ands is preserved in this novel radical species. Strangely enough, no stable ql-platinum that there is a preferred attack on the metal folfullerenyl derivative has been reported previ- lowed by immediate demetallation to give the ously, and the above-mentioned free radical is latter. An indirect approach, based on the metallathe only representative of monohapto-platinumtion of the radical dimer, was used to prepare fullerenyl compounds. The above-mentioned approach was success- q'-platinated fullerenyl radicals, see Scheme 111. fully used for the synthesis of qz-C-ioPt(PPh3)z, Because the fullerene-fullerene bond in this see Scheme 11, with the formation of two iso- dimer is very weak (ca. 10 kcal mol I) it can be mers being identified by the "P NMR spectrum. broken by irradiation with red, visible light The major isomer exhibited an AB system (a (630-680 nm). In fact, five distinguishable ESR pair of doublets) that corresponds to addition signals have been observed, each with differon the most strained a-b bond near the pole of ent g-factors and hfs constants, a, (due to couthe ellipsoid. The minor isomer exhibited one pling to phosphorus) which can be assigned to singlet that pointed unambiguously to the equiv- the regioisomers of rf-platinated phosphorylalence of both phosphorus atoms. This can hap- fullerenyl radicals (1 8). The reactions of C,,, and C,,, with the compen if the addition occurs on the c-c bond (the c-c bond is more removed from the pole and is plexes, HM(CO)(PPh,),, M = rhodium or indium, occur with high regio- and stereo-selecbisected by the plane of symmetry) (15 ) . Recently it was found that C,, can even react tivity by the replacement of one PPhl ligand to
Platinum Metals Rev., 1998, 42, (1)
20
C7oPt(PPh3)r
+
RHgPt(PPh&Br
-
Pt(PPhi)z
-RHgBr
R = PhzCHCHz
Yield: 85% Selected properties of C70Pt(PPh3)z Analytical data: found, % : C. 80.99; H, 2.24; P. 3.72 C1mH3cP~Pt.C7H8, calculated, %: C, 80.93; H, 2.34; P, 3.79
I
3'P NMR (toluene, 6 ppm): AB-system 6A= 25.5, 88= 22.9; J(PA,Pd = 24.5 Hz, J(Pn, Pt) = 4051 Hz, J(Ps,Pt) = 3875 HZ
-
I
~f-CmPt[(+)DIOP]
1l'-CiaPt(PPh2)2
+ (+)DIOP
~l~-CmPt[(+)Dl0P] + 2PPh3
Selected properties of qz-CloPt[(+)DIOP] CD spectrum (toluene, Cotton effect, he,,,nm): 312 (+),335 (-), 386 (+),496 ( + ) Optical rotation (toluene): [a]36s = -3.92 ( c = 0.0255)
r
Analytical data: found, % : C, 78.83; H, 1.96 C,clH3202PZPt, calculated, %: C. 79.06; H, 2.10 3'P NMR (THF, 6 pprn): AB-system, 6* = 8.28, 6e = 6.20; J(PA,PB)= 29 Hz, J(PA,Pt) = 3849 Hz. J(PB. Pt) = 3683 HZ
Scheme I1 Phosphine platinum complexes of C,O
give q2 metal derivatives on the [6:6] bonds. With C70y the double bond located on the sharp end of its ellipsoid is involved. A related diene-
hydride complex, HIr(COD)(PPh,)2,reacts in a similar way (19). The interaction of photolytically generated
Photolytic generation of R-fullerenyl free radicals R-Hg-R + CmR-Csd. R = -P(O)(OR)z,-BBSHSCZRZ
-
q*-Platinated phosphoryl fullerenyl radicals prepared via dimers 2R-Csa' R-Cba-Csa-R dimer hv
2R-Csb
I
qz-Pt(PPh3)z
k
R&c
The 5 Isomers (ESR):
+ Pt(PPh3h G
2.0017 2.0023 2.0025 2.0028 2.0032
o -R
I 1
(Ph3P)zPt Pt(PPh3)z
68.0
Scheme I11 Svnthesis of n'-elathated fullerenyl radicals via a radical dmer
Platinum Metals Rev., 1998, 42, (1)
21
Fig. 1 Molecular structure of the enantiomeric platinum fullerene complex
Bond length,
Bond
A
Angle
=)-Pt(l)-C(2) C( 1 )-Pt(1)-P(1 ) C(2)-Pt(1)-P(2) P(1)-Pt(1)-P(2)
I 1
2.09 2.12 2.28 2.26 1.51 1.44 Angle, deg
42.0 104.2 104.4 109.5
metric catalysts for use in various organic reactions. Additionally, as some platinum complexes are known to possess biological activity, this can be also expected for the platinum fullerenes. Thus, optically active compounds could be of interest in different fields, in part they have potential as materials for non-linear optics. Added to this, the circular dichroism of these compounds can provide information about the 1 g = 2.0026, U P = 66.7 gauss; electronic transitions in the fullerene core. 2 g = 2.0037, a,. = 64.25gauss; The first optically active organic derivatives of 3 g = 2.0027, up = 59.25 gauss fullerene have been reported by Vasella, with the species 1 being strongly predominant. Diederich and colleagues ( 21).These are sugarT h e parent phosphorylfullerenyl radical, fullerene derivatives whose circular dichroism *C,J'(0)(OAlk)Z, with g = 2.0023,ap = 63.5 spectra were recorded, and exhibited many gauss, formed more slowly from the iridium Cotton effects due to the electronic transitions complex compared with that from the platinum in C,,, itself. We took advantage of the opportunity to introanalogue (20). duce optically active ligands at the metal atom in q2-fullerene metal complexes and thus synOptically Active Organometallic thesise the palladium (22) and platinum (23) Fullerene Derivatives One of our main objectives has been the syn- Gocomplexes bearing the (+)DIOP ligand: [(+)1,4thesis of optically active organometallic fullerene 2,3-isopropylidene-2,3-trans-dihydroxyderivatives. These are interesting both in them- bis(diphenylphosphino)butane] at the metal. selves and as the possible precursors for asym- These were the very first optically active
(vide supra) dialkoxyphosphoryl radicals with the iridium fullerene complexes, q2-Cb,JrH(Y)PPh,, where Y = (CO)(PPh3) or (COD), at room temperature, was found to result in partial demetallation (attack on the metal) and addition (attack on the fullerene core) to give three isomeric phosphoryl(iridium)fullerenyl radicals, which have:
Platinum Metals Rev., 1998, 42,(1)
22
MOLECULAR ELLIPTICIT) MOLECULAR ELLIPTICIT)
WAVELENGTH, nm
Fig. 1 2 3
2 Circular dichroism spectra of the enantiomeric platinum and palladium C, derivatives: (q'-C,)Pt[(+)DIOP] in toluene ($-C,)Pd[(+)DIOP] in toluene ($-G)Pd[(+)DIOP] in dimethylformamide
organometallic fullerenes to be reported. They were prepared either by exchanging the triphenylphosphine ligand for (+)DIOP, see Scheme 11, or by direct synthesis from the fullerene, the diphosphine ligand, and the dibenzylideneacetone complex, Pd, (dba) ,: C,,,+ Pd2(dba),+ (+)DIOP 4(rf-Cw)Pd[(+)DIOP]
The molecular structure of the enantiomeric platinum fullerene complex was determined by X-ray study of the solvate with one molecule of cis-cyclooctene, see Figure 1, isolated after recrystallisation of the compound from a czscyclooctene-hexane mixture. The inclusion of cis-cyclooctene appeared to be absolutely necessary for the growth of good quality single crystals, but in spite of this, the solvate molecule had no close contacts with the fullerene molecule (23). Similar (+)DIOP complexes have also been prepared &om Go. Circular dichroism spectra were measured in toluene and in dimethylformamide, and several Cotton effects were found (unpublished results) which could be unambiguously attributed to the electronic transitions in the fullerene core, see
Platinum Metals Rev., 1998,42,(1)
Figure 2. In some cases the Cotton effects may be shifted due to interaction with the metal. In general, the wavelengths of the Cotton effects are close to those reported in (21). Finally, we have observed the catalytic effect of C,,Pd(PPh,), adsorbed on a porous carbon (sibunite) for the selective hydrogenation of a triple bond in 3,7-dimethyloctaene-6-yne-1-013 to a double bond in 3,7-dimethyloctadiene1,6-01-3 (linalool). This occurred more efficiently than with metallic palladium adsorbed on the same carrier under the same conditions (24). There is no possibility of asymmetric catalysis in this case, nonetheless there is a chance that the optically active fullerene palladium analogue would be a useful asymmetric catalyst for other hydrogenations which might result in chiral products.
Acknowledgement This work has been supported by grants from the Russian Foundation for Fundamental Research (RFFR), Scientific Programme "Fullerenes and Atomic Clusters", International Science Foundation (ISF MNR 000 and M N R 300),and the International Science & Technology Centre (Project 079).
23
References 1 E. Osawa, Kagaku (Kyoto), 1970,25,854 2 D. A. Bochvar and E. G. Gal’pern, Dokl. Akad. Nauk SSSR, 1973,209,610 3 H. W. Kroto, J. R. Heath, S. C . O’Brien, R. F. Curl and R. E. Smalley, Nature, 1985, 318, 162 4 W. Kraetschmer, L. D. Lamb, K. Fostiropoulos and D. R. Hufhan, Nature, 1990, 347, 354
5 P. J. Fagan, J. C. Calabrese and B. Malone, (i) Science, 1991, 252, 1160; (ii) Acc. Chem. Res., 1992,25, 134 6 V. I. Sokolov, (i) 181st Meedng of Electrochemical Society, St. Louis, 1992, Abstracts, FWL 662; (ii) Dokl. Akad. Nauk SSSR, 1992,326, 647
14 V. I. Sokolov, V. V. Bashilov and 0.A. Reutov,J. Organoniet. Chem., 1976, 111, C13 15 V. V. Bashilov, V. I. Sokolov, K. P. Butin and T. V. Magdesieva, Inorg. Chini. Acta, 1998, in press 16 V. I. Sokolov, Pure Appl. Chem., 1998, in press 17 For a survey of closely related ESR spectroscopy studies of fullerenyl radicals see: B. L. Tumanskii, Izv. RAN, Ser. Khinr., 1996, 2396; [Russ. Cheni. Bidl., 1996, 45, 2271, (Engl. Transl.)] 18 B. L. Tumanskii, V. V. Bashilov, N. N. Bubnov,
19
7 V. I. Sokolov, Mol. Muter., 1996, 7, 23 8 M. Sawamura, H. Iikura and E. Nakamura, 3. Am. Chem. SOC.,1996,118, 12850
20
9 D. T. Thompson, PlatinumMetals Rev., 1996,40, (11, 23 10 A. Hirsch, “The Chemistry of Fullerenes”, Thieme, Stuttgart, 1994
21
11 V. V. Bashilov, P. V. Peaovskii, V. I. Sokolov, S. V.
Lindeman, I. A. Guzey and Yu. T . Struchkov, Organometallics, 1993, 12, 991
22
12 T . V. Magdesieva, V. V. Bashilov, S. I. Gorelski,
V. I. Sokolov and K. P. Butin, Izv. RAN,Ser. Khim., 1994, 2153; [Russ.Chem. Bull., 1994, 43, 2034, (Engl.Transl.)] 13 V. V. Bashilov, B. L. Tumanskii, P. V. Petrovskii and V. I. Sokolov, Izv. RAN, Ser. Khini., 1994, 1131; [Russ. Chem. Bull., 1994, 43, 1070,
(Engl.Transl.)]
23
24
S. P. Solodovnikovand V. I. Sokolov, Izv. RAN, Se,: Khini., 1994, 938; [Rim. Chem. Bull., 1994, 43, 884, (Engl. Transl.)] A. V. Usatov, K. N. Kudin, E. V. Vorontsov, L. E. Vinogradova and Yu. N. Novikov, 3. Organomet. Chenr., 1996, 522, 147 B. L. Tumanskii, A. V. Usatov, V. V. Bashilov, S. P. Solodovnikov,N. N. Bubnov, Yu. N. Novikov and V. I. Sokolov, Izv. RAN, Ser. Khim., 1997, 870 [Russ. Chem. Bull., 1997, 46, 816 (Eng. Transl.)] A. Vasella, P. Uhlmann, C . A. Waldraff, F. Diederich and C . Thilgen, Aiigew. Chem., b i t . Ed. Engl., 1992, 31, 1388 V. V. Bashilov, P. V. Petrovslui and V. I. Sokolov, Izv. RAN, Ser. Khini., 1993, 428; [Russ. Chem. Bull., 1993, 42, 392, (Engl. Transl.)] V. V. Bashilov, P. V. Petrovskii, V. I. Sokolov, F. M. Dolgushin, A. I. Yanovsky and Yu. T. Struchkov, Izv. RAN, Ser. Khim., 1996, 1268; [Russ.Chem. Bull., 1996, 45, 1207, (Engl. Transl.)] E. M. Sul’man, V. G . Matveeva, V. V. Bashilov and V. I. Sokolov, Kiuct. Katal., 1997,38, (2), 274
Oxygen Dissociative Adsorption on Platinum Surfaces T h e chemical and physical processes occurring between gases and solids during surface catalysis are under continuous investigation and revision. Since platinum metals find wide use as catalysts, a n d readily chemisorb molecules and dissociate bonds, the interaction between platinum and oxygen was selected for detailed study. Surface kinetics of a heterogeneous reaction a r e usually described by t h e Langmuir model, which assumes that free adsorption sites on a surface are randomly occupied. Now, however, scientists at the Fritz-HaberInstitut der Max-Planck-Gesellschaft in Berlin have observed that oxygen dissociation is affected by nearby chemisorbed species ( T . Zambelli, J. V. Barth, J. Wintterlin and G. Ertl, Nature, 1997, 390, (6659), 495-497). Using a platinum( 11 1) surface, the distribution of chemisorbed oxygen was recorded by scanning tunnelling microscopy, a t intervals from 160 down to 50 K, after exposure t o 10 ’torr s oxygen. At 160 K the 0 atom coverage first formed randomly distributed adatom pairs, then as tem-
Platinum Metals Rev., 1998,42, (1)
peratures were lowered, the pairs formed clusters, which grew-into quasi-one dimensional chains, 10 to 50 A long, with branches at 120” angles. T h e chains formed an irregular network, followed by the appearance of triangular 0 clusters at the points where three chains met. T h e clusters had inhomogeneous distribution alongside large areas of bare platinum. Finally, triangular islands protruded from the surface. I t is assumed that there is a mobile adsorbed molecular precursor state, which is trapped and dissociated by already adsorbed 0 atoms - the active sites. At lower temperatures the precursor lifetime and its mean free path increase, giving it a higher probability of reaching an 0 atom. It is suggested that dissociation of the precursors is highest a t the ends of the chains. This apparent increased local reactivity and modification of the electronic properties near chemisorbed particles is a n important finding for the general description of catalytic reaction kinetics, and has relevance for most high temperature and pressure industrial heterogeneous catalyses.
24
Catalysts Play a Major Role in Development By A. E Chiffey Chemicals Dewlnprnent, Precious Metals Dix ision, . j o l i ~ i s n i W i a t t he?, Rovston
The second Anglo-Dutch Symposium on Catalysis and Organometallic Chemistry was held on the 26th September 1997, in Amsterdam, The Netherlands. The symposium was attended by more than 80 participants fi-om industry and universities in Britain and The Netherlands. A series of lectures was given on catalysis and its applications, and there were more than thirty poster presentations. This report highlights some aspects involving the platinum group metals.
the key reaction stages of oxidative insertion, hydrogen activation and the breaking of two carbon-sulfur bonds. The reactions have so far been performed under hydrogen pressures of 20 atmospheres and at a temperature of 100°C for 24 hours. While results from these systems have been encouraging and should help in the development of the next generation of hydrodesulfurisation catalysts, scaling these reactions to tonnage quantities is as yet impractical.
Catalysts with Bite Towards Cleaner Fuels Sulfur compounds, which occur naturally in crude oil, give the pollutant sulfur dioxide when burnt. Legislation, particularly in the U.S.A., is forcing the maximum sulfur limits in fuels to become progressively lower. This requirement, to produce more environmentally acceptable fuels, has lead Professor P. M. Maitlis of the University of Sheffeld to investigate metal catalysed hydrodesulfurisation reactions. Conventional methods of hydrodesulfurisation involve passing hydrogen with the fuel over Co/Mo/S or Ni/W/S catalysts at 300°C. However, in crude oil, alkyl substituted sulfur heterocycles, such as dimethyl dibenzothiophene (I), below, are, for steric reasons, more resistant to attack in these systems.
I
I
Q ,
(1)
Dibenzothiophene (DBT) R=Me
Professor Maitlis has shown that certain platinum catalysts have significant activity for removing dibenzothiophenes from crude oils. These catalysts, containing triethylphosphine or diphenylphosphinoethane, are involved in
Platinum Metals Rev., 1998, 42, ( l ) , 25-26
In chelate complexes with bidentate ligands the angle between the two donor atoms of the bidentate ligand and the metal centre is termed the ‘bite angle’. The importance of the bite angle in a series of complexes, was reported by Professor P. W. N . M. van Leeuwen of the University of Amsterdam, see I1 and 111. H
H
Distortions of this angle can affect reaction products, as was shown for the rhodium catalysed hydroformylation of alkenes. In this reaction, catalyst (11) with the phosphine ligand in the trigonal plane, gives a higher ratio of 1inear:branchedproducts than isomer (111). The size of the bite angle can be tailored by altering the length of the backbone between the donor atoms. Longer backbones tend to give larger angles, which reduce the strain in the chelate ring. Unfortunately, backbones which are longer than [C5] tend to give ligand bridged bimetallic compounds or (Rh-C) bound
25
organometallics. Ligands can be designed with rigid backbones resulting in greater control in the chelate structure. A range of diphosphines of the type (IV) has been studied to investigate the effect of the bite angle on product selectivity.
Ph2P
PPh2 (IV)
X = H, S, C(CH,)., SiMe:
Rhodium complexes containing these ligands have bite angles between 102 and 112". When these are used in hydroformylation reactions the 1inear:branched product ratio varies, the optimum performance being at a bite angle of 109". Deviations in the angle on either side of 109" gave both poorer yields and selectivities for the linear product. There are also secondary effects which should be considered with these ligands. Different substituents at X can contribute electron donating or withdrawing properties, which are known to modify the n:im product ratio. However, the overall effect of changing the bite angle is only small, giving just percentage changes in product yields, but for commercial processes the impact could be dramatic.
Ligands Designed for Catalysis The discussion of the relationship between structure and activity of catalyst was continued by P. Pringle of the University of Bristol, who described the design of ligands which would put metals into unusual environments.
Such ligands can modify the catalytic properties of a complex by, for example, introducing large steric bulk. Cage phosphine ligands have been prepared for this purpose from the simple
Platintini Metals Rev., 1998, 42, (1)
phosphine, PH,, see Equation (i). Palladium complexes containing cage phosphine ligands have shown good activity for catalysing hydrocarboxylation reactions. Similar ligands have been designed to give enhanced performance, by changing the groups bound to the phosphorus. Rhodium phosphite catalysts, [Rhl-P(OR),, have been shown to be 200 times faster than the corresponding rhodium phosphine catalysts, [RhI-PR,, in certain hydroformylation reactions. Unfortunately the (P-OR) bond in phosphites is susceptible to hydrolysis. Hence the search for more robust ligands has become an active area, and ligands such as biaryl diphosphites may be the answer. Binaphthite for example, shows good hydrolytic stability in tests when heated in acetone under reflux conditions. Once co-ordinated with metals, it has a greatly extended half-life (the halflife being the time when the catalyst decomposes (hydrolyses) to leave only half the active species). The same can be said of a range of novel water soluble phosphites. Putting the phosphorus donor in a crowded cage environment offers stabilisation and greater protection against hydrolysis. These phosphite containing materials have a combination of steric protection and exposure of the active sites that is necessary for successful catalysis. Research is continuing to improve the synthesis of these ligands and to extend the range of structures that are available.
Looking Ahead A little of the interesting work being carried out by both British and Dutch research groups has been highlighted here. Some of this work may well contribute to the development of industrial processes. With the close collaboration that is taking place between institutions on both sides of the North Sea the third Anglo-Dutch symposium, for which the date is yet to be confirmed, should certainly have much to look forward to. The third symposium is expected to take place in the U.K. in September 1998 and the organising chairman &om whom information may be obtained will be Professor Peter Maitlis of She5eld University, Fax:+44-(0) 141-273-8673.
26
Development of the Noble Metal/Oxide Coated Titanium Electrode PART I: THE BEGINNING OF THE STORY
By P. C. S. Hayfield Bickenhill, West Midlands, England
The titanium-based electrode was invented some fortyyears ago. Since then it has been incorporated into a wide variety of industrialprocesses on a huge scale, principally in the chlor-alkali industy. Deriving from industrial, as opposed to academic, work, the saga of its commercial exploitation has involved patenting and secrecy on a massive scale. Despite there being numerous contributors to the overall technology, just a f e w individuals are holders of the hundreds of patents that were taken out. It is not intended that this article should contain comprehensive details of patenis and other published literature, but rather be an attempl to portray, as accurately as possible, the excitement generated as the technology uiifolded. However, ii is bound to be inevitable, bearing in mind the complexities and the scope of commercial involvement, that not all readers will be satisfied with every detail, so apologies are yffered in advance to those who may inadvrrtentlLyfeel themselves slighted. By the early 1950s, the commercial production of titanium by the Kroll process was well advanced in both the U.S.S.R. and the U.S.A. However, around this time, the Metals Division of the British firm ICI decided to develop its own method of production, with the most likely principal use being seen as the aerospace industry. By the mid 1950s, following rapid development through the techniques of arc melting, consumable electrode melting and electron beam melting, a high quality, commercially pure titanium was being produced. It then fell to J. B. Cotton, who was Head of the Corrosion Section of the Central Research & Development Department in the Metals Division of ICI, to assess both the corrosion and electrochemical properties of this newly commercially-available metal. Cotton and his team, by then having gained an enviable reputation for selecting successful copper-based alloy tube that came to be used in the condenser cooling systems of ships and power stations, were soon able to demonstrate using jet impingement and other test ~
I'latiriuni Metals Rev., 1998, 42,( l ) ,27-33
methods - that titanium possessed both exceptional corrosion and erosion resistance towards seawater (1).
The Noble MetaYTitanium Bielectrode Concept Titanium anodises when it is used as the anode in a range of non-halide containing aqueous environments. This usually results in the growth of thin films of oxide which exhibit interference colouring when viewed in white light. After anodising, the anode can no longer pass useful current. It was observed that if unanodised titanium was attached to an already anodised electrode, current passed only until the fresh titanium had anodised. When a soluble metal, such as copper, was attached to the anodised titanium, current would flow until all the copper had dissolved; this is the concept behind the now widely adopted titanium anode basket used for metal plating applications. In some aqueous halide solutions, including seawater, titanium exhibits the phenomenon of anodic breakdown corrosion. Cotton experimented with attaching
27
Fig. 1 Platinum electroplated titanium rod anodes as used typically in the cathndic prntectinn nf water boxes in power generating plant
carbon to titanium to bleed off current and hence minimise the risk of possible breakdown corrosion. But he soon came to appreciate that attaching carbon resulted in an anode being produced, and from there it was a short step to spot welding a small piece of platinum wire to the titanium and showing that current passed through the platinum. The concept of the platinum coated titanium bielectrode had thus been recognised. Fortunately for Cotton, within his group there was a highly experienced plating specialist called C. H. Angel], who was able to successfully coat adherent platinum onto titanium at a time when it was considered difficult to plate any metal adherently onto titanium. As there was a possibility of commercially exploiting such a platinised titanium bielectrode in cathodic protection, patent protection was sought (2). After several months, it came to the attention of the Metals Division that, totally independently of the ICI work, an employee of Magneto Chemie in The Netherlands, H. B. Beer, had taken out a patent on rhodium plated titanium, see Table I for major milestones in the development ( 3 ) .Its priority date was just a few weeks before that of the ICI patent. It is thought that Beer, working in the unusual surroundings
PIatirzunz Metals Rev., 1998, 42, (1)
of a building constructed around a disused windmill, had come across the bielectrode concept during studies on making scents. The consequence of this situation was that an agreement was struck between the small-sized Magneto Chemie and two Divisions of the much larger ICI organisation, General Chemicals (chlorine producers) and Metals, under which the development of titanium-based electrodes to replace graphite electrodes in chlorine cells was to be shared. Beer was to work on coating formulations while others were to concentrate upon assessing the commercial viability of the coatings on titanium electrodes. The agreement stayed in force for several years, not being terminated until 1965. International Nickel and Engelhard gave early assistance during these formative years in the development of titaniumbased electrode technology.
Electrodeposited Platinum Coatings Although the management of the Metals Division of ICI permitted the registering of a first patent (2), there was not even lukewarm enthusiasm for the platinum electroplated titanium electrode which was being offered commercially for cathodic protection uses, ahead of its utilisation in the chlorine cell industry.
28
The argument ran: platinum is expensive, and titanium both expensive and relatively scarce, so how can a bielectrode comprising the two metals ever be commercially viable, compared with existing lead-based and other electrodes? However, the possibility that platinised titanium might operate at substantially higher current densities than existing anodes, encouraged Cotton's enthusiasm. This optimism was supported by several other workers in the cathodic protection industry. G. Waite was possibly the lirst to mount electrodes, for trial, on a ship's hull, and this use was also helped when J. H. Morgan included a section on titanium-based electrodes in his book (4); one illustration showed an electrode vigorously evolving chlorine at high current density. The product was technically improved over many months, but the questions of how much platinum to apply and how long the coating would last, went unanswered. At that time it was the vogue in the metallurgical industry to try radiotracer technology of the kind used by Losev and colleagues at the Karpov Institute in Moscow (3,but short term results were inconclusive. Accurate determination awaited results from long term polarisation mals, lasting severalyears, at the ICI seawater corrosion laboratory at Brixham, and at the Brighton Seawater Laboratory of the S. E. Board of the Central Electricity Generating Board, where intermediate non-destructive monitoring of residual platinum loading was independently performed. In broad terms, the anodic corrosion rate for platinum electroplate coatings in seawater was found to be between 1 and 2 pg for every ampere hour of elecmcity passed (pg A 'h I). Put another way, only between one and two millionths of the current passed through the anodes, used for chlorine evolution, was involved in platinum dissolution. In industry there was no time to wait for the results of these long polarisation trials - so the first commercial anodes were platinum coated, in a sodium hexahydroxyplatinate bath, until visually there seemed to be continuous coverage. This occurred after deposition of about 55
Platinum Metals Rev., 1998, 42, (1)
g m I , which is a nominal 2.5 pm thickness. At the time it was thought that as platinum was so noble the bielectrode would be able to last indefinitely.
Superimposed AC on DC R. Juchniewicz of the Gdansk Polytechnic (6, 7) suggested that the effects of AC ripple superimposed on current from commercial transformedrectifiers was likely to shorten significantly the life of the commercial platinised titanium bielectrode, and this indeed was worrying news. By then the manufacture of platinised titanium bielectrodes for cathodic protection had been transferred to Marston Excelsior Ltd, a wholly-owned Metals Division subsidiary. To preserve the reputation of the new product, it was felt necessary to advise electrode users to limit superimposed AC ripple to not greater than 5 per cent of DC; in some instances this necessitated the provision of costly smoothing equipment. But it was later found that superimposed AC ripple was not as serious as initially alleged (8),the explanation involving the AC frequency. Juchniewicz's work used AC of 50 Hz and lower frequencies, whereas the ripple from most industrial D C supplies is 100 Hz and higher. Platinum forms a surface oxide during anodic polarisation which, while thin, is capable of reduction to finely divided platinum if depolarised over a long enough period. At 50 Hz and lower frequencies, including stops/starts, platinum oxide will reduce to a form in which it can be lost mechanically. But depolarisation at 100 Hz and higher is too short a period for the reduction to occur, and no example has even been recognised where superimposed ripple has been the cause of premature electrode failure.
Brine Dilution Effects Unexpectedly high platinum corrosion occurred to electrodes placed in tidal estuaries. The anodic corrosion rate of platinum rises from 1 to 2 pg A ~ ' h' to 50 or higher pg A-'h-', for chloride concentrations varying from near 30 g 1 I (seawater) to around 2 to 3 g 1 I, respectively. In effect, platinum forms an equilibrium or quasi
-
29
Table I
Important Dates 1958
Rhodium electrodeposition on titanium (Beer)
1958
Platinum electrodeposition on titanium (Cotton et al)
1960
Painthhermal decomposition method of coating (Angel1et al)
1965
First mixed metal oxide coatings (Beer)
1967
Second mixed metal oxide coatings (Beer)
1968
First titanium-based electrodes (70130 Pt1lr coated) in commercial chlor-alkali cells (chlorate)
1984
Titanium-based anodes in electrogalvanising
1986
Titanium-based anodes in the cathodic protection of rebar in concrete
equilibrium state when evolving chlorine, and a rather different state for oxygen evolution. During cojoint oxygen and chlorine evolution, which occurs in dilute brine, there is interference in the formation of surface layers and this leads to accentuated metal dissolution.
Deposits In one of many well-documented applications, large numbers of rod-type platinised titanium anodes, see Figure 1, were installed to protect a steel jetty in the Middle East. With the years, shifting sands led to some anodes, initially in clear water, becoming silted over. Whenever this happened, platinum was lost preferentially and the underlying titanium began to corrode. This was explained by the formation of high acidity near the surface of the electrodes, which were struggling to operate at high current density.
Organics As if superimposed A C ripple, brine dilution and local acidity were not enough unexpected hazards to affect the life of platinised titanium electrodes, it was disappointing to have to add others, including organics, to the list. A first instance came when platinised titanium was supplied in small-coil form as auxiliary anodes as part of the nickel plating on the insides of kettles. For seemingly unexplained reasons at the time, such electrodes had particularly short lives. The
Plariiiunr Metals Rev., 1998, 42, (1)
cause was traced to a particular organic brightener addition, naphthalene trisulfonic acid (9). It was hoped that this was an isolated example, but it was not. In retrospect, organic chemists should not have been surprised that a platinised titanium anode used in thc cathodic protection of a steel vessel containing a feedstock of dilute brine and sugar failed prematurely. However, it was totally unexpected to those involved. In desperation, a succession of different types of coated titanium, described later, were used, but all, to varying extents, had anodic dissolution rates significantly increased in the presence of sugar. The various decomposition products of sugar, including fructose and gluconic acid, do not exert similar activation. The list of specific organics which have a deleterious effect on the anodic behaviour of noble metal/oxide electrocatalysts continues to increase. It now includes certain oils, wetting agents and concentrated seaweed.
Improvements to Technology In the manufacture of most platinum electroplated titanium, the titanium is first chemically etched to form a surface with reentrant angles -- to aid the mechanical adhesion of subsequently applied coatings. Even this simple process of chemical roughening has involved much development. Beer was the first to suggest that an equi-axed titanium grain size of 0.03 to 0.05 mm was the
30
optimum, a specification now used worldwide. Etchants have ranged widely, including hydrochloric acid at ambient temperature (3 days), hot oxalic acid (8 hours), hot sulfuric acid (1 hour) to the so-called Piontelli alkaline anodic etch (few seconds). The acid etches cause the formation of a surface film of electrically conducting titanium hydride, but once samples are washed in water and exposed to air, a skin of electrically resistive titanium oxide soon forms. Surfaces partially coated with hydride and oxide cause coarse nucleation of the deposit during subsequent platinum electrodeposition. A simple and expedient way to overcome such coarse, porous deposits, is first to coat the titanium with a thin electrically conducting layer using the paintlthermal decomposition process described later. This so-called paintlelectroplate method (10) is now widely practised, resulting in improved coating adhesion, less porous deposits and visual platinum coverage at much lower overall loading than hitherto possible. The decreased porosity confers significant improvement to resistance against the coating being undermined in acidic environments.
Metallurgically Co-processed Platinised Titanium In parallel with the development of the platinum electroplated titanium electrode at the Metals Division of ICI, another part of the organisation sought to promote uncoated titanium sheet electrodes for the formation of “starter cathodes” in the copper refining industry. Here, titanium was required to be attached to copper hanger bars. This cannot be done by autogenous welding as brittle intermetallics form. Therefore, A. C. Barber of ICI decided upon encapsulation of copper by titanium, so that clad bars could be spot welded to titanium sheet. To achieve such cladding an ingot was prepared, comprising a core of copper and an outer skin of titanium, which could be metallurgically coprocessed (hot extrusion followed by cold drawing) to make the copper-cored titanium. A variation of the sequence was to wrap platinum foil around the titanium to make platinised copper-
Platinum Metals Rev., 1998, 42, (1)
cored titanium ( 1 1). By this route much thicker platinum can be applied to titanium than is possible by electrodeposition, and further, the coatings are not porous. An excellent example of the product is the platinised niobium used for cathodic protection of a North Sea oil platform (1 2). It has been suggested recently that platinised titanium has been a commercial disappointment (1 3). While it is true that there are now electrocatalyst coatings which are displacing platinum in respect of cost, durability and other characteristics, platinum electroplated titanium has been, and continues to be, a highly successful commercial product. Not only does the high hardness (occluded hydrogen) of the platinum confer important abrasion resistance, but in a wide range of applications, the product has become predictable and dependable, and unlikely to be replaced. Probably a longer term assessment than can be written a t present will view platinised titanium as an important phase in the development of later generations of coatings. Until the advent of the bielectrode, both wrought platinum and clad platinum copper had restricted use because of cost. T h e advent of more affordable electrodes greatly increased both the size and diversity of application, and the electrochemical characteristics of the metal have also been much clarified. In the 195Os, the situations where platinum was found, anodically, to dissolve unexpectedly fast were not foreseeable. Nevertheless, the conditions which affect platinum electroplate also have relevance to later generations of coatings.
Paint/Thermal Decomposition Coating Methods Platinum electroplated titanium, with the platinum in passivated mode, is characterised by a high chlorine overpotential (14), see Figure 2, making it unattractive for use over graphite in the chlor-alkali industry, to lower manufacturing costs. Angel1 was the first to propose an alternative to electrodeposition as a method of coating (1 5). He put forward the concept, not novel in itself, of taking a solution containing a
31
I
I 16-
Platinum electrodeposited onto titaniLm
1
W 1 5 V v)
c L
'
14-
_I
5 z
k 13-
2 W
;
1.2
-
1,l
-
V _I
W
/ I
I
I I I
I
l I
l I
Noble metal and mixed m e t a l oxide on t i t a n i u m by p a i n t / t h e r m a l duomoosition
CURRENT CURRENT
Chlorate. Merrury-type diaphragm chlorine and m e m b r a n e cells t y p e chlorine c e l l s
Fig. 2 Tafel plots for various anode surfaces in 22 per cent brine at 70°C to illustrate the considerable saving in anode potential gained by changing from graphite to titanium-based electrodes
soluble noble metal salt, applying it as a paint to the titanium surface and then heating it in air to decompose the salt to the metallic state. An element of good fortune existed, in that at the temperature for thermal decomposition, 400 to 500"C, titanium does not significantly oxidise in air. By comparison, the painting technique cannot be readily applied to niobium because its inherent rate of oxidation is too fast. Displayed in Table I1 are results that had accrued in the Metals Division of ICI by February 1963. These take the form of chlorine overpotentials at 1 and 10 kA m current density, in 22 per cent brine, for a range of electrodeposited and painthermal decomposition coatings. It is necessary to be cautious in understanding the information. At that time it was
Platinurn Metals Rev., 1998,42,(1)
CURRENT
believed that 70/30 platinum/iridium (Pt/Ir) electroplate was an alloy when in fact it is a fine scale mixture of platinum and iridium. More importantly, and certainly not appreciated at the time, all painthhermally decomposed coatings, with the singular exception of platinum, were in noble metal oxide, rather than metallic, form. All the paint/thermally deposited coatings exhibit low chlorine overpotential, and in addition, ruthenium electroplate possessed low chlorine overpotential. Again, it has been suggested (1 3) that because of the simplicity of the paintithermal decomposition route the method is trivial, but while it may be a simple concept, its practical execution is complex in detail. It may now seem straightforward to dissolve completely a noble metal salt in a solvent, of either water or alcohol, but in the early 1960s this was not so. A close interplay was required between the producer and the user to achieve full solubility. Adherent deposits produced by the paint/thermal decomposition route are so thin, that any undissolved particles form major local discontinuitieswhich may weaken the durability of the electrode. Even in modem-day coating plants, paints must be shaken or barrelled over several days and then decanted before the liquid is considered usable. When painting there is a natural instinct to want to shake or stir paint before its application, but for electrodes this must always be resisted. Paints generally have a short shelf life, and any storage should be at low temperature, less than say 5°C. In the Metals Division of ICI, in the early 1960s, it was possible to purchase an oily, resinate-based platinum-containing paint which was used in the ceramics industry. However, Beer preferred to make up his own composition. A typical route, later patented, might include dissolving chlor-platinic acid in an alcohol, such as amyl alcohol, and then adding a natural oil, linalool, which has the rather exotic name of 'ex Bois de Rose'. After repetitive paintithermal decomposition sequences to build up a significant loading, Beer proposed improvement to the coating by a post heat treatment (16). While the charge was still at the final decomposition
32
I
Table II Chlorine Overpotential Measurements for Electrode Surfaces, in February 1963 Overpotential in saturated brine
Overpotential in saturated brine at 7OOC. mV Surface Platinum paint (05X) 70/30 Pt/lr paint (IR-1) Platinum paint Ruthenium paint Iridium paint Rhodium paint
1 kA m
10 k A m Z
12 11 8
24 25 11 12 41 43 41 42 30 28 40 42
8 21 27 25 27 19 17 26 28
Surface Flame sprayed platinum Nominal 70/30 Pt/lr electroplate Platinum electroplate Ruthenium electroplate Iridium electroplate Rhodium electroplate
temperature, ammonia was introduced, followed by butane, and finally the atmosphere changed back to air for 60 hours, prior to cooling to ambient temperature. T h e ammonia/butane part often led to a ‘flash over’ or slight explosion as rapid local oxidation ensued. When, for a few months, the Beer route was introduced into production at the Witton site of the Metals Division, it was considered prudent on safety grounds to have a fire tender standing by should the processing get out of control. Nowadays it is commonplace to accept both
1kAm2 71 57 43 60 38 42
18 20 32 33 213 22 1
I
10kAmZ 27 1 195 81 106 63 93 28 33 52 92 306 324
noble metal oxides as well as noble metals as electrocatalysts,but this was not always the case, as there was a reluctance to move away from platinum. The second part of “Development of the Noble MetaVOxide Coated Titanium Electrodes”, will examine the history of the platinum-containing paints used to coat electrodes in mercury cells, diaphragm and chlorate cells for the production of chlorine, and the advent of Ru0,/Ti02 electrodes. It will be published in the April 1998 issue of Platinum Metals Review.
References 1 J. B. Cotton and B. P. Downing, Transactions of the InstituteofMarine Engineers, 1957,69,311-319
2 J. B. Cotton, E. C. Williams and A. H. Barber, Bnzish Patent 877,901; 1958 3 H. B. Beer, British Patent 855,107; 1958 4 J. H. Morgan, “Cathodic Protection: Its Theory and Practice in the Prevention of Corrosion”, Leonard Hill (Books) Limited, London, 1959
5 V. V. Gorodetskii, M. A. Dembrovskii and V. V. Losev, Zh. Prikl. Khinz., 1963, 36, 1543-1 549 6 R. Juchniewicz, First International Congress on Metallic Corrosion, Buttenvorths, London, 1962, p.368 7 R. Juchniewicz, Platinum Metals Rev., 1962, 6, (31, 100
Platinum Metals Rev., 1998, 42, (1)
8 R. Juchniewicz and P. C. S. Hayfield, Third International Congress on Metallic Corrosion, MOSCOW, 1966, 73-82 9 M. A. Warne and P. C. S. Hayfeld, Trans. Metal Finish., 1967, 45, 83-92 10 M. A. Warne and P. C. S. Hayfield, British Patent 1,351,741; 1970 11 A. C. Barber, British Patent 1,457,511; 1973 12 R. M. Vennett, R. W. Seager and M. A. Wame, Mater. Perfown., 1983, 22, 22-30 13 G . K. Chandler, J. D. Genders and D. Pletcher, Platinum Metals Rev., 1997, 41, (2), 54-63 14 J. A. Bittles and E. L. Littauer, Corros. Sci., 1970, 10,2941 15 C. H . Angel1 and M. G. Deriaz, British Patent 885,819; 1960; British Patent 984,973; 1963 16 H. B. Beer, British Patent 964,913; 1962
33
ABSTRACTS of current literature on the platinum metals and their alloys PROPERTIES
CHEMICAL COMPOUNDS
Optical Properties of Platinum Particles Synthesized in Microemulsions
BiYRhBr": A Subbroniicle with Molecular [ (RhBi;)Br~]Clusters
1. F. RIVADULLA, h4.
Ed. B i g / . , 1997,36, (18)! 197 1-1 973 The halogen-rich Bi suhhromide Bi7RhBrx,which consists of discrete molecular clusters of [ IRhBi,; Br,], is reported. In this novel cluster, the Bi atoms are arranged as a pentagonal bipyramid around the central Rh atom, and the IRhBr-; core is then surrounded b y a distorted, square Br\ antiprism. This is in contrast to currently known metal-rich Bi subiodides.
(;.
VERGARA, hi. C. BLANCO,
and J. KIVAS, J . Phys. Clieiri. B, 1997, 101, (44), 8997-9004 Nanoparticles (- 4 nm) of Pt, synthesised from HJ'tCI,, and hydrazine in water-in-oil microemulsions, show a maximum in optical absorption at 220-256 nm, depending on the reaction medium. Ageing uf the solutions changed the optical properties due to cluster formation, as did heating without hydrazine. This colloidal Pt formation was catalysed by light. M A. LOPEZ-QUINTEW
Structure Sensitivity of Methane Dissociation on Palladium Single Crystal Surfaces K. KI.IER,
1. S. HESS and R.
C.;
HEKMAN,
J.
ChJlI.
PhJS.,
1997,107, (lo), 4033-4043 Pd single crystals are active for the C-H bond dissociation of CH, at 400-600 K. Dissociation rates varied by an order of magnitude in the order Pd( 11 1) < Pd(311) < Pd(679), while the activation energies ranged from 32-34 kJ mol I for Pd (1 11) and Pd(31 l), to 44 kJ mol ' for Pd(679). Defects on the Pd(679) surface provide a driving force of 26 kJ mol ' compared to the smooth planar P d ( l l 1 ) surface, and 22 kJ mol ' compared to Pd(3 11).
Effect of Sputtering Pressure of Pd Underlayer on the Perpendicular Magnetic Anisotropy in
hl. KtiCli,Ai~geZo.C h i f . ,Irlt.
Rooin-Teittperattire M o l t e u Ruthenium Tris(bipyricline) I[.
h i . . \ s ~ Iand
K \Y AlLIRRAl', bforg. C&iif.,
Salts
of
1997, 36,
(22), 5118-5126 Attaching poly(ethy1ene glycol)-mono(methy1ether) (MePEG; MW = 350) chains to [Ru(hpy)\]'*complexes via 4,4'-hipyridine ester linkages produced room temperature, highly viscous, molten salts of the f w m [Ru(hpy),(hpy(CO2MePEG-750)2) ,](CIO1): (A7 = 0, 1 and 2). Data are given for the adiabatic Ru(IIIII1) and Ru(III1) electron self-exchange reaction rates in thc purc melts.
Reactivity of Ku( H ) ( H2)CI(PCy:,)r with Propargyl and Vinyl Chlorides: New Methodology to Give Metathesis-Active Ruthenium Carbenes
Coma Multilayered Thin Filiiis
T E WILHELhl. 1' K . Htil.DERKAIN. S . N . BRO\Y'h' and 1997, 16, (1 8), and s.-R. joo, ZEEE Truirs. M ~ i g ~ i . , R. H. t i R U B B S , Or~uifoii/L'r~llllicS) 3867-3869 1997,33, (5), 3655-3657 The magnetic properties of CoiPd multilayers were The reaction of (RuCl,(COD)],, PCy8,H, and NEt. in sec-hutyl alcohol gave Ru(H)(H:)Cl(PCy,): in 95% found to depend on the sputtering pressure of the Pd underlayer. Perpendicular coercivity of the multi- yield. Following a novel insertion-elimination pathway, this hydride can react with propargyl or vinyl layers increased as the Id' underlayer deposition preshalides to make metathesis-active vinyl and alkyl carsure increased from 6 to 25 mTorr, with the increhenc spccies with the formulae (PCy,),CLRu=CHment of the coercivity being larger for films with CH=CR, and (PCy,).CLRu=CHR, respectively, with thinner Co suhlayers. The interface anisotropy energy decreased from 0.390 to 0.255 erg cm I, due to interface tertiary propargyl chlorides giving very high yields. roughening of the multilayers. T h e magneto-elastic effect contrihutcs to the perpendicular anisotropy. ELECTROCHEMISTRY H.-S. OH, B . - I . LEE
Microstructural Analysis of PdlPtIAdPd Ohmic Contacts to InCaPlGaAs D. G. IVEY, K. %I IANG, Z. ABID. s. EICHER and T. 1'. LESTER, J. M a t e r . Sci.: Mater. Elertroii., 1997,8, (5), 28 1-288 T h e microstructure of low resistance PdiPtiAuiPd pohmic contacts to InGaPiGaAs heterofunction hipolar transistors was studied during annealing. T h e Pd and Pt reacted with the lnGaP emitter layer and GaAs base layer to form (Pt,Pdl ,),(In,.GalJ P (0 5 x, .v 5 l), PtAs2and PdGa. Minimum values of 0.104.12 R mm were achieved after annealing a t 4 15-440°C for contacts both with and without Zn.
Platiiiunr Metals Rew., 1998, 42, (l ), 34-39
Carbon Moiioxicle Electrooxiclation on Porous Pt-Ru Electrodes in Sulphuric Acid A. S . ARI(:O, I 40 times, to give 4-ethyltoluene at the rate of 0.92 mmol h ~ ' . The marked increase in the hydrogenation rate was suggested to be due to an increase in the reaction zone and the appearance of new active sites.
Electrochemical Oxidation and Reduction of Rhodium and Iridium Complexes with Fullerenes Cm and C70 L. I. DENISOVICH, S. M . PEREGUDOVA, A. V. USATOV, A. L. SIGAN and Y. N. NOVIKOV, Izv. RAN, ser. Khim.,
1997, (7), 1308-1313 Electrochemical studies on Rh and Ir complexes of the fullerenes C,, and C:, showed that they are capable of oxidation and reduction. The metallo-fullerene complexes were generated in situ froni the interaction of C,,, and Ci0with Rh and Ir hydridocarbonyl phosphine complexes, HM(CO)(PPhl),. The effect of the structure and C 0 2on the redox properties of fullerene complexes is discussed.
Dip-Coated Ru-V Oxide Electrodes for Electrochemical Capacitors Y. TAKASU, T. NAKAMURA, H. OHKAWAUCHI and Y. MURAKAMI, Elecrrochem. SOC.,1997, 144, ( 8 ) ,
3.
2601-2606 Dip-coated RuO?-VO, electrodes were prepared and found to have a large electrochemically active surface area, with an electrode of RuO,(33%)-VO,(67%)/Ti calcined at 450°C having the highest voltammetric charge of- 50 times that of a RuOdTi electrode. This large surface area is characterised by the dispersion of fine V20i particles, the formation of RurV01 and the probable presence of ultrafine RuO,. The voltammetric charge of the electrode of 162 m C cm-' at 0.3-1.1 V at a sweep rate of 50 mV s ' corresponds to 0.76 protons contributed to the adsorption on every Ru ion.
Porous Ruthenium Oxide Electrode Prepared by Adding Lanthanum Chloride to the Coating Solution Y . MURAKAMI, 'I-. KONDO, Y. SHIMODA, H. KAJI, Alloys Contpd., 1997, X.-G. ZHANG and Y. TAKASU,
3.
261, 176-181 Porous R u O D i electrodes were prepared from RuOZLazO,lTi (Ru:La = 7:3) electrodes by the complete dissolution of La ions in HSO,, from the well complexed Ru-La oxide. The voltammetric charges of these electrodes were 20 times larger that those of conventional RuOJTi electrodes prepared by the thermal decomposition method.
-
Platinum Metals Rev., 1998, 42, (1)
PHOTOCONVERSION Photochemistry of M(PPI)HI (M = Ru, 0s; PPa= P(CH2CH2PPh2)r):Preparative, NMR, and Time-Resolved Studies R. OSMAN, D. I. PATTISON, R. N. PERUTZ, C. BIANCHINI, J. A. CASARES and M. PERUZZINI, A m . Chem. Soc.,
3.
1997, 119, (36), 8459-8473 Ru(PP,)HLand Os(PP,)Hz were prepared and their photochemistry studied by various techniques. Key features include: the scavengingof N2by the cyclornetallation product of Ru(PP3);the totally different kinetic selectivity of Ru(PP,) and OS(PPI)compared with Ru(dppe)*;the enhanced reactivity of Ru(PP,) towards benzene and HSiEt,; and the insertion of Os(PP,) into aliphatic C-H bonds of T H F and alkanes.
The Photovoltaic Stability of Bis(isothiocyanato)ruthenium( 11)-bis-2,2'-bipyridine4,4'-dicarboxylic Acid and Related Sensitizers 0 . KOHLE, M. GR,~TZEL, A. F. MEYER and T B. MEYER, Adv. Mater., 1997, 9,( l l ) , 904-906 Endurance tests are reported for sealed photovoltaic cells with cis-Ru"(LH,),(NCS), (LH2= 2,2'-bipyridyl4,4'-dicarboxylic acid) as sensitiser. After > 7000 h of illumination with visible light at 1000 W m ' light intensity, the performance was unchanged. This was due to the speed of the interfacial redox processes during photovoltaic operation. They conclude that the electrolyte in solar cells should contain high iodide concentrations and not dissolve the sensitiser.
Photo- and Thermo-Chromism of a Ruthenium(I1) Complex and ViologenContaining Polymer Film M. SUZUKI, M. KIMURA, K. HANABUSA and H. SHIRAI,
Chem. Commun., 1997, (21), 2061-2062 A polymer film comprising a Ru(I1) complex and a viologen-containing partially quaternised poly( 1vinylimidazole) film is described. Upon light irradiation in air, the film colour changed from orange to blue, then reverted to orange on standing in the dark. Similar changes occurred upon heating (blue) and cooling (orange). Blue to orange changes were slower. The blue colour is due to the formation of viologen radicals formed by electron transfer from the photoexcited Ru(I1) complex to the viologen.
Chemiluminescence in the Oxidation of Sodium Anthracenide and Pyrenide by Ru'" Complex and B. A. TISHIN. Izv. RAN, Ser. m i n i . , 1997, (3), 609-611 Chemiluminescence (CL) during the oxidation of Na organocompounds (Na'R-) (R = anthracene or pyrene) in THF by Ru(bpy)3'' (1) has been studied. Using CL emitters, excited singlet states of polycyclic aromatic hydrocarbons 'R* (2) and Ru(bpy),"' (3) were identified and a mechanism for their formation was proposed. It is suggested that (3) can be formed by reacting Ru(bpy)," with Ru(bpy)," or by energy transfer from (2) to (1).
R. G. BULGAKOV
35
ELECTRODEPOSITION AND SURFACE COATINGS Mesoporous Platinum Films from Lyotropic Liquid Crystalline Phases G. S. ATTARD, P. N. BARTLETT, N. R B. COLEMAN, J. M. ELLIOTT, J. R OWEN and J. H. WANG, Scieme, 1997,
278, (5339), 838-840 Pt was electrodeposited onto polished Au from a liquid crystalline plating mixture consisting of temary systems of a non-ionic surfactant, such as octaetheleneglycolmonohexadecyl ether, H2PtC1,and H,O at 25-65°C. The surfactant was removed with deionised H1O. Transmission electron micrographs showed Pt films consisting of a uniform highly porous hexagonal lattice structure with cylindrical holes. The diameter of the holes can be controlled either by changing the chain length of the surfactant or by adding a hydrophobic additive to the plating mixture.
Fabrication of Epitaxial Diamond Thin Film on Iridium K. OHTSUKA, H. FUKUDA, K. SUZUKl and A. SAWABE,Jpll.
3.Appl. Phys.,Pan2,
1997,36, (9AIB),L121PL1216 Smooth diamond thin films were epitaxially grown o n a (001) Ir surface in a two-step direct current plasma CVD process, using ion irradiation pretreatment and diamond growth. The epitaxial areas of the diamond films, with a mean thickness of 1.5 pm, acted as optical mirrors. The films had an average roughness of 1nm, a low C content, except for diamond, and an area of > l mm'. The depth profiles of the thin films were studied using Confocal Raman spectroscopy.
-
-
APPARATUS AND TECHNIQUE Photoluminescent Oxygen Sensing on a Specific Surface Area Using Phosphorescence Quenching of Pt-Porphyrin and I. OKURA, Anal. Sci.,1997, 13, (4), 535-540 An optical sensor for 02-pressure measurements was developed based on the phosphorescence quenching, by O,, of Pt octaethylporphyrin incorporated in uolvmer films. This sensor had a good ouerational stability and < 10% photobleaching even after storage for > 1 year in the absence of light at room temperature. s.-K. LEE
Simultaneous Aniperometric and Potentiometric Detection of Inorganic Anions in Flow Systems Using Platinum and SilverlSilver Chloride Electrodes Z . CHEN
and D. B. HIBBERT, A I ~Chinz. . Acts, 1997,
350, (1-2), 1-6 An electrochemical detection system for inorganic ions in flow systems uses both amperometric Pt and potentiometric Ag/AgCI electrodes, coupled with ion chromatography. After separation by anion-exchange chromatography, C1 , Br , I , SCN and S 2 0 , ' were determined potentiometrically with a detection limit of 1 x 10 ' M while, simultaneously, NO2-,Br ,I and SCN were determined amperometricallywith a detection limit of 1 x 10 I' M. Ion-interaction chromatography separated and detected Br ,NO, and SCN .
Improved Performances of InGaP Schottky Contact with TilPtlAu Metals and MSM Photodetectors by (NHl)nS,Treatment Solid-State Electron., 1997, 41, ( l l ) , 1715-1719 Studies are reported on the effect of (NH,).S . ,trearment of InGaP on thc high performance of GaAs metal-semiconductor-metal (MSM) photodetectors with InGaP buffer and capping layers. The surface states were reduced by S passivation which improved the InGaP Schottky contact with TiiPtiAu. T h e improved dark current and insensitive response with incident optical power were demonstrated by suitable process control of S passivation.
c.-T. LEE, M.-H. LAN and c.-D. TSAI,
Hydrogen Gas Detection via Photothermal Deflection Measurement Rev. Sci. ItZstnltll., 1997, 68, (9), 3544-3552 A thermal wave H 2 sensor containing a thin film polyvinylidenefluoride film coated with a thin Pd layer was examined by transverse optical beam deflection spectroscopy. The sensitivity to H. resulted from thermal boundary condition changes at the gas-film interface and depended upon the thermophysical properties of the gas. Concentration measurements of 0.1% H2in the presence of a balanced air mixture at room temperature indicated possible sensitivities approaching 100 ppm. K. KALLI, A. OTHONOS and C. CHRISTOFIDES,
~~
Comparison of the Gold Reduction and Stripping Processes at Platinum, Rhodium, Iridium, Gold and Glassy Micro- and Carbon ‘MicroMacrodisk Electrodes A. M. BOND, s. KRATSIS, s MITCHELL and J MOCAK, Analyst, 1997, 122, (lo), 1147-1152 The reduction of Au(II1) and the oxidative stripping of Au in 0.1 M HCI + 0.32 M H N 0 3were studied at Pt, Rh, Ir, Au and glassy C disk electrodes. Pt was the best electrode material and a Pt disk electrode, 50 pm in diameter, generated a maximum (stripping) peak:reduction current ratio, with a sharp, symmetrical, and a very well defined Au oxidation signal.
Platiizu?n Metals Rev., 1998, 42, (1)
Electrocatalytic Oxidation and Flow Amperometric Detection of Hydrazine at an Elmtrop1ymerized4-Viny~pyridinfla~~adi~ Film Electrode and E. WANG, E/ect,oaizalysis, 1997, 9, (1 5), 1205-1208 Electropolymerisation of 4-vinylpyridine onto the surface of a glassy carbon electrode followed by electrodeposition of Pd onto the polymer modified electrode surface gave a poly(4-viny1)pyridineiPd film electrode used for the electrocatalytic detection of hydrazine. Compared with Pdiglassy C electrodes, this electrode displays improved mechanical stability and higher sensitivity with a detection limit of 0.026 ng at 0.5 V and a linear range of 0.2 pM to 1 mM.
T. LI
36
Stabilization of an Osmium Bis-Bipyridyl Polymer-Modified Carbon Paste Amperometric Glucose Biosensor Using Polyethyleneimine J. JEZKOVA, E. I. IWUOHA, M. R. SMYTH and K. VYTRAS,
HETEROGENEOUS CATALYSIS Characteristics of PtlH-beta and PtlHMordenite Catalysts for the Isomerization of n - Hexane and H.-K. WEE, Catal. Today, 1997, 38, (2), 235-242 Bifunctional Pt/H-beta (1) and Pt/H-MOR catalysts were prepared under various pretreatment conditions and tested in the isomerisation of n-hexane. (1) gave a higher yield of high octane dimethylbutanes and greater selectivity than the commercial Pt/H-MOR. This was because a larger number of acid sites were available to bulky reaction intermediates and the Pt clusters were well dispersed to give a proper balance between metallic centres and acid sites in (1).
Electroanalysis, 1997, 9, (13), 978-984 Biosensors were constructed by the immobilisation of a glucose oxidaselos-bis-bipytidyl poly(4-vinylpyridine) polymer electrostatic complex within C paste electrodes, and used as amperometric glucose sensors in the presence or absence of a stabilised polyethyleneimine (PEI). The PEI enhanced the stability of the electrode and its sensitivity. The biosensors showed rapid response, improved substrate specificity, high affinity for glucose, renewable surface and a broad pH range of high sensitivity.
J.-K. LEE
Screen-PrintedRuthenium Dioxide Electrodes for pH Measurements
Catalytic Removal of Nitric Oxide with Hydrogen and Carbon Monoxide in the Presence of Excess Oxygen
and M. MASCINI, Anal. Chini. Acta, 1997, 351, (1-3), 143-149 Cheap, disposable potentiometric p H sensors based on Ru02have been prepared by a highly reproducible, simple, low temperature firing screen-printingmethod on plastic supports. Fast measurements were achieved with good sensitivity (5 1 mVlpH) in acidic and neutral solutions with a linear range of response up to pH 8. There was also no interferencefrom alkaline cations, common anions and complexing ligands, but the pH measurements were strongly affected by the presence of reducing compounds. R. KONCKI
Immobilization of Ruthenium Tris-Bipyridyl Complex for Chlorine Gas Detection Sens. Actuators B, Chenz., 1997, 38-39, (1-3), 195-201 Methods for the physical immobilisation of a trisbipyridyl Ru complex (Ru-TRL) have been examined for the use of TRL, with a fibre-optic based sensing system for C12(g).Polyvinyl pyrrolidone and silicone rubber matrices allowed rapid response to CL with detection limits of 0.675 and 1 ppm, respectively, under Nz. Silicone rubber showed a greater change in fluorescence intensity and speed of response and was less susceptible to humidity changes. Its detection limit, however, rose to 5 ppm in air. T. E. BROOK and R. NARAYANASWAMY,
Fabrication and Characterizationof Ru-Doped Ti02 Composite Membranes by the Sol-Gel Process Muter. Lett., 1997, 33, (1, 2), 101-105 The effects of Ru on the grain growth, pore size and particle diameter of Ru doped TiO, composite membranes were studied on samples prepared by a sol-gel process. The doped TiO, sols were prepared by destabilisation of the colloidal solution process. The thickness of the doped membranes was 50-1000 nm, with a crack-free microstructure and narrow particle size distribution even after calcination at < 800°C. The mean particle size of the Ru doped membrane was smaller than that of the undoped TiO, membrane. D.-S. BAE, K . 4 . HAN and s.-H. CHOI,
Platinum Metals Rev., 1998, 42, (1)
and T. TANAKA, Appl. Surf. Sci., 1997, 121/122,273-277 The removal of NOx with H2in the presence of excess 0 2 was studied over Pt catalysts. Pt/zeolite had a high conversion efficiency but was readily poisoned by CO and hydrocarbons (HCs) and formed NzO as a byproduct. Reducing the oxidation efficiency of Pt gave an improved catalyst, Pt-Mo-Na/SiOZ, which has a higher temperature range of NOx conversion, forms less N 2 0and removes NOx with HCs, HI and CO. K. YOKOTA, M. FUKUI
Investigationon Active Sites in Pt-Mo on Silica Catalysts for Reactions of Hydrocarbons with Hydrogen G . LECLERCQ, S . PIETRZYK, T. ROMERO, A. E L GHARBI, L. GENGEMBRE, J. GRIMBLOT, F. AISSI, M. GUELTON, A. LATEF and L. ECLERCQ Ind. Eng. Chenz. Res., 1997,
36, (lo), 4015-4027 Physico-chemical studies were performed on PtMo/SiOzcatalysts with the same (Pt + Mo) metal atom content but various Mo:Mo + Pt ratios. Pt was completely reduced to metal in H, at 400-7OO0C, independent of the reduction temperature, but only a fraction of Mo was reduced, depending on temperature. Two types of reaction occurred: cyclohexane dehydrogenation, alkane isomerisation and cyclisation, with the rate determining step occurring on Pt; and alkane hydrogenolysis, faster on Pt-Mo than on Pt, due to preferential adsorption on Pt-Mo sites.
Hydrogen Cyanide Synthesison Polycrystalline Platinum and 90 : 10 Platinum-Rhodium Surfaces A. BOCKHOLT, 1. S. HARDING
and R. M. NIX, J . Chem.
SOL.,Faraday Trans., 1997, 93, (21), 3869-3878
HCN has been synthesised from CHi-based feedstocks at relatively low temperatures (< 780°C) and pressures (0.02-0.15 Torr) over pure Pt and Pt-lO%Rh alloy model catalysts. Maximum activity was observed for CH4-NH,-OI in a 1:1:0.5 ratio over Pt. Rh inhibited HCN production and Pt-1O%Rh alloy gave lower HCN yield and selectivity.
37
Vehicle Exhaust Control. I. Influence of Oxygen Content on Methanol Deep Oxidation over Pd/y-A120, and R. WANG, ChineseJ. Catal., 1997, 18, (5), 414-417 Studies on the effect of 0, content on MeOH deep showed that when I'd is preoxidation over P~/.I-ALO, sent in a reduced state on the support, the MeOH oxidation activity and deep oxidation selectivity of the catalyst increase with increasing O?content. However, when the amount of 0, increases to the extent that the Pd is transformed into an oxidised state, the activity and selectivity decrease. MeOH oxidation to formaldehyde was easier over P d - 0 . B. ZHU
Preparation of Palladium Colloids in Block Copolymer Micelles and Their Use for the Catalysis of the Heck Reaction S.KLINGELHOFER, W. HEW%, A. GREINER, S. OESTREICH, s. FOKSTEK and M. ANTONIETTI, J. Awl. Chenr. sac.,
1997,119, (42), 10116-10120 Highly stable colloidal dispersions of nanometre sized Pd colloids have been prepared in block copolymer These micelles of polystyrene-6-poly-4-vinylpyridine. polymerimetal hybrids can be readily dissolved and handled in organic solvents and were successfullv used for the Pd-calalysed C-C coupling of aryl halides with alkenes (Heck reaction). They showed similar reactivity the low molecular weight pd complexes uaditionally used, but were far more stable, remaining catalytically active even after 50,000 turnover cycles without Pd black formation; thus the products may be suitable for pharmaceutical and electro-optical use.
Rh/One-Atomic Layer Ge02/Si02as a New Flow Flow for Ethyl Acetate Hydrogenation at a Low Pressure K. OKUMURA, K. ASAKURA and Y.IW'ASAWA, Chem. Left. Jpn., 1997, (lo), 985-986 Rh,(CO),, precursor was supported on one-atomic layer Ge02/Si02to give, after reduction at 423-523 K, a new FWone-atomic layer GeOJSiO. catalyst. This was active for the selective ( 5 80%) hydrogenadon of ethyl acetate to EtOH under mild reaction conditions (473 K P(HJ = 6 . 6 kI'a), whereas RhibulkGe02and Rh/Si02were inactive for this reaction. The by-product acetaldehyde was produced at higher prereduction temperatures.
Synergism in the Reaction of CO with 0 2 on BimetallicRh-Pd Catalysts Supported on Silica and v DIAZ, J. Chenr. SOC.,Faraday Trans., 1997,93, (21), 3887-3891 The activity of Pd-Rh/SiO, catalysts, prepared by various methods, towards the oxidation of CO with Oi was studied, and a synergistic effect was found to exist between the two metals when the catalysts were prepared by sequential impregnation. This effect was highly dependent on the pretreatment of rhe catalysts. The coexistence of oxidised Rh and reduced Pd was necessary for the synergistic effect to occur. P. AKAYA
Platinum Metals Rev., 1998, 42, (1)
Catalytic Decomposition of N20 over Supported Rhodium Catalysts: High Activitiesof Rh/USY and Rh/AlrO:Iand the Effect of Rh Precursors K YUZAKI,T. YARIMIZU, s.-I. ITO and K. KUNIMORI, Caral. Lerr., 1997, 47, 173-175 The catalytic decomposition of N,O to N, and O1was studied over supported Rh catalysts. RhiAI20, and Rh/USY zeolite catalysts prepared from Rh(NO\)$ had higher activities than the previously reported RhlZSM-5 and RNZnO. RNUSY(N0,)was the most active with a T O F of 26.0 x 10 's I . The activity of RhiALO, was far lower when prepared from RhCII, despite high dispersion of the Rh, probably due to residual CI in the catalyst.
Hydroformylation of Hex-1-ene in the Presence of Rhodium Carbonyl Catalysts Immobilised on Polymeric Organosiloxanes N V. KOLESNICHENKO, G. V. 7'RREKHOVA, A. T. TELESHEV. E. I. ALEKSEEVA and E v SLIVINSKY, Izv. RAN, Ser.
Khint., 1997, (6), 1155-1157 Hydroformylation of hex- 1-ene was catalysed by acacRh(CO)! immobilised on highly active and stable polymeric organosiloxanes. The effects of the nature of the oligomers, the oligomer ratio and the Rh:oligomer ratio in the polymer on the synthesis and catalytic properties of this system were investigated. CURRENT by POb'mer-Bound Catalysis Rh6 Carbonyl Clusters. Selective Hydrogenationof Carbonyl Compounds in the Presence of co and HIO
MIZUGAKI, K. EBII-ANI and K. KANEDA, ~ p p l ~. u r j . Sci., 1997, 121/122, 360-365 meCURRENT ofm,(~-) with functionalised polyCURRENT styrenes gave pobmer-bound cluster complexes which showed high catalytic activity for the hydrogenation of various aldehydes to the corresponding alcohols. The activity depended on the length of the spacers and on the basicity and hydrophilicity of the polymers. These reactions took place in a triphase system of H 2 0 , organic phase and polymer which simplifies work-up procedures. T.
,(,
Hybogenation Isotherms Of Adsorbed Carbon Species on a RdA1203 Catalyst after co Adsorption and CO/H2 Reaction H. ~ M I M. , N A \ W ~ A. . K. BENCHEIKHand D. B ~ C H I ,
R~tll.SOC.Chiin. Belg., 1997, 106, (5), 245-252 Studies of the surface adsorbed C suecies formed on a 3.5'l/uRuiA120acatalyst after chemisorption of either CO or COIH. at 478 K are reported. Exposure to COiHe resulted in rapid formation of various adsorbed species on the Ru and the A1201.The transient isothermal hydrogenation to C H Ishowed three species: linear, bridged and gem-dicarbonyl CO species on the Ru particles. Some adsorbed CO species on the metal and a carbonate on the support are not hydrogenated to methane. Linear C O is the main adsorbed species on the surface. Exposure to CO/Hl gave the same species, except the gem-dicarbonyl and carbonate. Some C,H, species formed on the Ru surface and a formate species formed on the support.
38
HOMOGENEOUS CATALYSIS Palladium-Catalyzed Amidocarbonylation A New, Efficient Synthesis of N-Acyl Amino Acids M.BELLER,M.ECKERT, F.VOLLMULLER,S. BOGDANOVIC and H. GEISSLER, Angew. Chem., Int. Ed. Engl., 1997,
36, (13/14), 1494-1496 I’d halides have been shown to catalyse amidocarbonylation reactions under mild reaction conditions of 80°C and 10 bar CO. Pd(I1) bromide was the most active, giving the highest ever turnover number of 25,000 (mol product per mol Pd-cat) and turnover frequency of > 400 (mol product per mol Pd-cat per hour) seen for this reaction. This system can also produce, in good yield, a much wider range of N-acyl amino acids than with Co catalysts.
Synthesis and Catalytic Application of [Rh(PPhs)a([9]aneS3)]PF6 and J. D. E. T. WILTON-ELY, Organometallics, 1997,16, (21), 45174518 The reaction of [RhCl(PPhl),] with [9]aneS1(1,4,7trithiacyclononane) and NHJ‘F, gave [Rh(PPh,),( [9]aneS3)]PF, (1) which undergoes a range of ligand substitution and oxidative-addition reactions. (1) also effectively catalyses the demercuration of bis(alkyny1)mercurials giving the product in 94% yield, which is higher than obtained with the conventional catalysts [RhCl(CO)(PPhI)r]and [RhCl(PPh~)l]. A. F. HILL
Asymmetric Transfer Hydrogenation Catalyzed by Diamine-Iridium(I) Complexes s.-I.INOUE, K. NOMURA, s. HASHIGUCHI, R. NOYORI and Y . IZAWA, Chem. Lett. Jpn., 1997, (9), 957-958
A series of Ir(1) catalysts was prepared from [IrCl(cod)]>and chiral 1,l -di@-anisy1)ethylenediamine derivatives and used for the asymmetric transfer hydrogenation of a range of aromatic ketones in 2-propanol. Good yields of 2 97% and enantioseJ. J. J. JULIETTE, I. T. HORVATH andJ.A. GLADYSZ, Angew. lectivities of 2 93% were observed in the presence of Chewz., Int. Ed. Engl., 1997, 36, (15), 1610-1612 The “Teflon greaseball” catalyst [RhCl{P[CH2CH2- KOH at room temperature, comparable to enan(CF2),CF3]I)3] (1) wasprepared from [{RhCl(cod)J2] tioselectivities obtained by Rh(I) and Ru(I1) catalysts. and P[CH2CH2(CFr)sCF1]1 in 94 % yield. The catalyst is highly soluble in CF,C,F,, and catalyses a vari- ELECTRICAL AND ELECTRONIC ety of organic transformations. For hydroboration ENGINEERING reactions, catalyst loadings of 0.0 1-0.25 mol% were effective under mild conditions (25-40°C, 1-40 h) Synthesis of the PZT Films Deposited on Ptgiving turnover numbers of 8500, high yields and Coated (100) Si Substrates for Nonvolatile good enantioselectivity. Products can be extracted Memory Applications with organic solvents, and the solution of (1) reused. A. KUMAR, M. R. ALAM, A. MANGIARACINA and Catalytic Asymmetric Hydrosilylation with M.SHAMSUZZOHA,~. Electron. Mater., 1997,26, (1 I), (Triazoliny1idene)rhodium Complexes 1331-1 334 The growth of ferroelectric lead zirconate titanate Containing an Axis of Chirality (PZT) films deposited on Pt-coated (100) Si substrate D. ENDERS, E. GIELEN and K. BREUER, Tetrahedron: by the pulsed laser deposition technique was studAsynznzetry, 1997, 8, (21), 3571- 3574 ied using various deposition conditions. The best crysChiral (triazoliny1idene)rhodiumcomplexes have been talline structure was observed for PZT deposited at synthesised with a diastereomeric excess of de = 575°C in 450 m Torr 0, partial pressure. The rem91-97%. They are effective for the asymmetric nant polarisation and the retained polarisation of hydrosilylation of methyl ketones giving alcohols with the ferroelectric capacitors were 13 and 20 pC cm ’, enantiomeric excesses of 5 44% and 5 90% yield. The respectively. selectivity was dependent on reaction temperature Oxygen Diffusion in Pt Bottom Electrodes and the substituents on the chiral ligand, but independent of the reaction time or amount of catalyst. of Ferroelectric Capacitors Yields however were dependent on the latter two Y. MATSUI, M. SUGA, M. HIRATANI, H. MIKI and conditions. Y. FUJISAKI,JpZ. J.Appl Phys., Pun 2, 1997,36, (9A/B), L1239-L1241 Hydrogenation of Phenylacetylene Catalyzed diffusion through the grain boundaries of by a Dihydridorhodium Complex, Oxygen Pt films during the crystallisation annealing of Pb(Zr, [RhHz(PhZNS)(PPb)i] T i ) 0 3(PZT) was studied for the stacked structure of N. KAMEDA, Y. HASEGAWA and T. YONEDA, Nippon PZT/Pt/TiN, using two Pt films with different strucKaguku Kaishi, 1997, (8), 560-564 tures. For the TiN film exposed to air after deposiThe homogeneous hydrogenation of phenylacetylene tion, the Pt film consisted of polycrystalline grains was performed in the presence of [RhH2(Ph2NI)- with random orientation, while on the TiN film with (PPh&] catalyst under 1 a m H2.Phenylacetylene was Pt sputtered in vacuo the grains were columnar (1 11)reduced to styrene in toluene with the catalytic activ- oriented with continuous grain boundaries normal to ity reduced by increasing reaction temperature and the substrate. Differences in the grain boundary structures determine the O2diffusion rate in Pt which was the addition of triphenylphosphine or 1,3-diphenyldesirably lower on the film exposed to air. triazene. Internal alkynes were not hydrogenated.
Transition Metal Catalysis in Fluorous Media: Practical Application of a New Immobilization Principle to Rhodium-CatalyzedHydroboration
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Platinum Metals Rev., 1998, 42, (1)
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NEW PATENTS ELECTROCHEMISTRY Aniorphous Alloy for Electrodes JAPAN SCI. &TECHNOLOGY CORP.
European Appl. 80 1,15 1A An electrode material for anode electrolysis uses a platinum group metal based amorphous alloy of composition NMlood%CubP,, where N M is at least one metal selected from Pd and Pt, with 1-30% Pt; a, b, and c are atomic % so that a+b = 3045, b/a = 3-7 and c = 18-25. A temperature width A T v of the electrode material in a supercooled liquid region is t 70 K, and A T y = T,-T,, where T, and T, are the crystallisation and glass transition temperatures.
Photocatalyst for Photoreactions World Appl. 97126,99 1A A photocatalyst comprises T i 0 2implanted with Cr, V, Cu, Fe, Mg, Ag, Pd, Ni, Mn and/or Pt ions below the oxide surface in the amount of 1 x 10” ionsig of oxide. The presence of metal ions extends the range of light absorption into the visible, so that reactions can be catalysed by UV to visible light irradiation. The catalyst is used for photoreactions, such as butene isomerisation and nitrogen oxide decomposition. PETROLEUM ENERGY CENT.
Electrode for Chloralkali Cell U.S. Patent 5,645,930 An electrode has a substrate with a porous heterogeneous catalytically active primary phase coating, with a substantial internal surface area having a Pt group metal matrix mixed with a particulate material; a secondary intermediate coating of an adhesion promoting polymer and an electroless metal plating catalyst; and an outer phase metal reinforcing coating. The coatings impart durability to the electrode which has low H2overpotential and is more poison-resistant. DOW CHEM. CO.
Electrochemical Device DAIICHI DENKO K.K. Japaiiese Appl. 91155,157 An electrochemical device comprises an anode made of a Pt-plated conductive porous base material for generating O 2by H z O electrolysis, a cathode consuming 0 2 by the generation of H,, and a solid polymer electrolyte membrane working as a proton exchange membrane. This electrolyte contains fine catalyst particles and is filled in the pores of the base material. This device is used for 0, enrichment, deoxygenation devices or humidifying elements.
Electrode Film Junction Body TANAKA KIKINZOKU KOGYO K.K.
Japanese Appls. 9/165,689-90 An electrode film junction body for electrolysis is produced by ion exchange absorbing Pt ions to a cationic exchange resin film and depositing a Pt metal layer on the surface of the film using a reducing agent. The Pt ion source is a complex salt consisting of a Pt amine complex ion and a hydroxide ion. The process removes CI ions to depress HC1 generation, a by-product, so promoting a stable exchange reaction. The quality of the Pt-film junction body is maintained.
ELECTRODEPOSITION AND SURFACE COATINGS Platinum Coatings U S SEC OF ARMY U.S. Patent 5,650,202 A uniform Pt coating is formed on a non-conductive substrate, such as a glass slide or Si wafer, by immersing the substrate with hydrophobic C black in H2PtCI, and H C H O to reduce the acid and form metallic Pt on the surface. Hydrophobic pretreatment of C black powder with a C F , gas plasma is also claimed. This method is simple, effective and inexpensive, and is used in making mirrors for lasers, protective coatings, in corrosion prevention and electroless plating on non-conductive substrates.
Plating of Iridium YAZAKI COKP. Japanese Appl. 9113,190 Novel Ir plating is carried out using a plating bath containing SeO,’ ions. It is used for plating Ir layers with excellent adherence on electronic components.
Thin Platinum Film MITSUBISHI MATERIALS CORP.
Japanese Appl. 911 57,85 1 A raw material, for forming a thin Pt film by metal organic chemical vapour deposition, is obtained by mixing (1,5-dimethyl-l,5-~yclooctadienyl)Pt with an electron donating compound. It has superior pyrolysis and a very high deposition rate. The Pt film is produced with high efficiencyand purity. Thin Pt films can be formed on an underlying electrode for a dielectric substance used in memory semiconductor devices.
Coating Liquid
Electrode for Electrolysis
SUMITOMO METAL MINING CO.
Japanese Appl. 91157,879 An electrode for electrolysis has a substrate underlayer containing Ta and a covering layer containing Ir, T a and Si oxides, provided through the underlying layer on the substrate. Production of the electrode by pyrolysing the underlying and covering layers is also claimed. The electrode has stability, a prolonged life and superior durability. It is used to electrolyse an electrolyre containingat least one organic compound.
Japairese Appl. 91161,561 A coating liquid (1) used to form dark-colour transparent conductive films is a dispersion of conductive oxide fine particles, which contain Ru oxide, Ir oxide, or Ru- or Ir-based pyrochroa of < 50 nm in diameter, in a polar solvent. The conductive films are formed by coating (1) on a substrate and coating over with a solution containing the polymer of partially hydrolysed alkyl silicate, followed by firing at < 400°C.
T D K CORP.
Platinunt Metals Rev., 1998, 42, (l ), 40-44
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APPARATUS AND TECHNIQUE NOx Sensor NGK INSULATORS LTD. European Appl. 79 1,825A A device to measure NOx in the exhaust from petrol or diesel engines includes a main pumping cell to control the partial pressure of O 1and electrodes contacting the process gas, with at least one comprising a platinum group metal containing 0.01-1% Au. This Au-Pt alloy has a low activity towards NOx, which allows elimination of 0 2 so that NOx can be measured with high stability and accuracy.
Selective Detection of Carbon Monoxide Japanese Appl. 911 13,501 A material for the selective detection of C O gas contains WO,, MOO,and a Pt group metal catalyst which gives a reversible yellow colour change. C O is selectively detected in atmospheres containing mixtures of C O gas and ethanol. KURABE K.K.
Solid Electrolytic Oxygen Pump Japanese Appl. 9/127,05 1 A solid electrolytic 0, pump has an oxygen ion conductive material used as a partition wall with a noble metal electrode on each surface and a Pt electrode collecting net. The Pt nets simultaneously decrease electrode material resistance and electrode reaction resistance. T h e pump has superior Or partial pressure controllability. The 0, concentration in N, or Ar is very low, with O2partial pressure of 10 'latm. The pump is used in producing semiconductors, in controlling 0, strength in alloying processes, heat treatment, inert gas production or anaerobic atmosphere control in fermentation or microorganism culture. MITSUBISHI JUKOGYO K.K.
HETEROGENEOUS CATALYSIS Reduction of NOx in Diesel Engine Exhaust BASF A.G. European Appl. 779,093A A catalyst for the reduction of NOx in diesel engine exhaust gas comprises a spinel of formula Ca,ZnbAl,04, mixed with Pd, Pt, Rh, Ru, Os, Ir or Re and/or rare earth, such as Ln, Ce, V, Ti, Nb, Mo, W and/or their salts; where a + b + c = 3 and a > 0, b > 0 and c > 0. The spinel is preferably impregnated with C e 0 2in an amount of 0.5-15 wt.%, especially 1-8 wt.%. T h e catalyst has high stability and effectively purifies exhaust gases.
Non-Selective Oxidation Catalyst INST FRANCAIS DU PETROLE
European Appl. 780,15 6A A non-selective oxidation catalyst comprises a monolithic substrate, an inorganic refractory porous support, and an active phase containing Ce, Zr, Fe and at least one metal selected from Pd and Pt. The Pd and/or Pt content is > 3 g I-' of the catalyst and the porous support is 200-400 g 1-' of the catalyst. This catalyst is used for the catalytic combustion of fuels, such as HC, CO, H2and their mixtures, and especially natural gas, for automotive exhaust gas de-pollution.
Platinum Metals Rev.,1998, 42, (1)
Reduction Purification of NOx COSMO OIL CO. LTD. European Appl. 78 1,592A T h e reduction purification of a NOx-containing exhaust gas involves contacting the gas with a catalyst in an oxidative atmosphere containing excess 0, and in the presence of at least one reducing agent selected from a hydrocarbon and an 02-containing organic compound. The catalyst comprises Sn, and Ru,Pd, Rh and/or In. The process effectively reduces NOx in the presence of excess 0, and in a gas containing H,O vapour or SO:.
Staged Fuel Injection INST. FRANCAlS DU PETROLE
European Appl. 784,188A A staged fuel injection catalytic combustion process comprises a catalytic zone containing a catalyst made of a monolithic substrate, a porous refractory inorganic oxide-based support and an active phase consisting of (based on weight of porous support) 0.>20% Ce, 0.01-3.5% Fe and 0-20% Zr together with Pd and/or Pt in an amount of > 3, preferably 5-15 g I-' of the catalyst. It is used for catalytic combustion in radiant panels and tubes, catalytic stoves, gas turbines, etc. The process has high stability during operation and start-up and provides improved performance, especially in the catalytic combustion of methane, CO, H2 and their mixtures.
I.C.E. Exhaust Gas Treatment FORD MOTOR CO. European Appl. 785,017A A catalyst system for the conversion of hydrocarbons, C O and NOx in exhaust gas from an I.C.E. comprises first, second and third catalyst bricks consisting of a porous substrate and a metallic catalyst arranged in series in the exhaust gas passage downstream of the manifold. T h e first brick, coated with Pd, has the smallest volume, and is closely coupled to the exhaust gas manifold and is positioned adjacent to and spaced apart from the second catalyst by 5 10 inches. T h e system provides good conversion even at cold-start and has high temperature durability.
Catalytic Converter System FORD MOTOR CO. European Appl. 7 8 6,2 84A A closely coupled catalytic converter system exhibiting rapid light-off and low start-up emissions has two catalytic elements. T h e first has a thermally stable washcoated substrate with > 100 g fif of large particle Pd deposits and is closely coupled to the exhaust manifold of an I.C.E. The second is a washcoated substrate with deposited metals efficient at reducing HC, C O and/or NOx emissions from an exhaust gas stream with higher O2capacity than the first element.
selective Hydrogenation of ~ i ~ l ~ f i ~ ~ PETROLEUM pH*LLIPS .'CO ' European Appl. 792y685A PETROLEUM CO A catalyst for the selective hydrogenation of 3-12C diolefins comprising Pd metal and/or Pd oxides, at least one alkali metal iodide, and at least one inorganic support is prepared by impregnating and heating in a non-oxidising gas at 300-600°C. The catalyst has a high activity, selectivity and catalyst life.
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Emission Control from Gasoline Engine
Colloidal Palladium-GoldAlloy Catalyst
WorldAppl. 97120,619A Emissions from a fuel direct injection type gasoline engine are controlled using an exhaust purifying catalyst containing a Pt group metal, such as Pt, and transition metals. The purification of exhaust gas with a wide variation in the composition and temperature, resulting from frequent change of the air:fuel ratio, can be simplified.
World Appl. 97133,690A A colloidal Pd-Au supported catalyst for the selective production of vinyl acetate from ethylene, acetic acid and O2 is produced by forming an aqueous solution of H20-solublePd and Au compounds, dispersing the solution in a hydrophobic solvent to form a microemulsion which is treated with a reducing agent, impregnating a support with the mixture, and drying. A uniform microstructure of Pd and Au on the supDort is achieved bv reduction of the metals before impregnation. The catalyst has improved selectivity over an extmded time span.
ICT CO. LTD
HydrodechlorinationCatalyst World Appl. 97120,629A The durability of a supported Group VIII metal hydrodechlorination catalyst is improved by treatment with a non-elemental halide compound, such as a chlorohydrocarbon or an alkali(ne earth) metal chloride, but which is not a mineral acid. A preferred catalyst is Pt or Pd on an oxide support, and the metal, in the zero valent state, mainly resides at the surface and is vi!ible under a microscope having a resolution of 5 A. AKZO NOBEL N.V.
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Hydrogenation Catalysts World Appl. 97125,142A Hydrogenation catalysts comprise supported Pd and an alkali metal. They are used for the hydrogenation of halofluorocarbons and hydrohalofluorocarbons to produce hydrofluoroalkanesfor use as CFC replacements in refrigeration and air conditioning. Product selectivities of > 95% are obtained.
IMPERIAL CHEM. IND. PLC
Production of Mono-olefins UNIV. MINNESOTA World Appl. 97126,987A T h e production of mono-olefins, used as gasoline octane improving components, from gaseous 2C+ para& hydrocarbons is reported. This involves reacting the hydrocarbons and 0,in the presence of a highly active and selective Pt catalyst modified with Sn and/or C u and supported on a ceramic monolith.
Improved Diesel Trap Performance CLEAN DIESEL TECHNOL. INC.
World Appl. 97128,358A The operation of a diesel engine equipped with a diesel trap is improved by combusting the fuel-air mixture and introducing at least half of a lt' group metal directly into the exhaust gases, with a combustible organic liquid, to partially load the diesel trap for more effective regeneration. The Pt group metal is present at 0.05-1 .O ppm as an alcoholate, sulfonate, etc., to reduce the balance point temperature. At least half of an auxiliary metal composition, selected from Ca, Mg, Mn, etc., is introduced into the fuel prior to combustion.
Hydrogen Peroxide Production ERlK BENGTSSON PROCESS DESIGN
WorldAppl. 97132,811A H2 and 0, are contacted in the presence of a Pd or Pt supported catalyst in a hydroquinone solvent (1) which has no H,O phase and a limited solubility for the HIOLproduct and HiO. (1) can also contain HSO, or HJ'O, to improve the yield and reaction velocity. H202,used in cellulose bleaching, is formed at 50% concentration and 5 95% yield.
Platinum Metals Rev., 1998, 42, (1)
HOECHST CELANESE COW.
"ydrogenolysis
PETROLEUM CO
E. I . DU PONT DE NEMOURS & CO.
U.S. Patent 5,629,462 The catalytic hydrogenolysis of fluorohalo(hydro)carbon(s) is achieved at 1255350°C using a hydrohalogenation catalyst prepared by impregnating a C support (with an ash content of < 0.2 wt.%) with 5-95 wt.% Au, and 95-5 wt.% of Ru, Rh, Pd, Os, Ir and/or Pt, and heating at < 350°C to dry the composition and reduce the metals. For the hydrogenolysis of 2,2dichloro-l,I, 1,2-tetrafluoroethane, a selectivity of 97.7% and conversion of 33.4% were obtained. PETROLEUM CO CO SupportedPETROLEUM L E E R BROS. CO. DIV. CONOPCO INC.
U.S. Patent 5,643,849 A catalyst consisting of Pd and Bi on a C support is prepared by suspending 1-10 wt.% Pd (on a C support) and 0.1-10 wt."/oBi in H,O at a Pd:Bi ratio of 6:l-6:2; and adding 5-15% (by wt. of the catalyst support on C) of an aldehyde. The catalyst is used for the oxidation of an aldose to a salt of aldonic acid. It gives high selectivity, high oxidation rates and a low coloured product. Conversions of lactose to Na lactobionate of 99.7% can be achieved.
AlkanelCycloalkane Isomerisation Catalyst PHILLIPS PETROLEUhi CO. U.S. patent 5,654,254 A Group VIII catalyst containing CI is prepared by impregnating at least one of Pt, Pd and Ni, and ALO, as the support, with at least one organoaluminium chloride, heating the material obtained in an inert gas and treating with a hydrogen chloride-containing gas at 630-750°C. T h e catalyst is used in alkane/ cycloalkane isomerisation. It has high activity which is maintained for long periods.
Catalytic Partial Oxidation of Hydrocarbon UNIV. MINNESOTA U.S. Patent 5,654,491 The catalytic partial oxidation of a hydrocarbon, for a rapid and effective production of oxygenate(s), comprises passing a feed gas mixture containing 9 and a hydrocarbon with at least one normal 2 4 C alkane, such as butane, through a Group VIII metal (preferably Rh and Pt) catalyst gauze structure of 2 80% transparency. T h e exit gas mixture comprises C O and CO, with a total C selectivity of 5 70 molecule YOC. Liquid fuels and chemicals from lower alkanes associated with remote sources of natural gas are obtained.
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Production of 3-Chloropropyltrichlorosilane Pentenoic Acid Preparation SHINETSU CHEM. IND CO. LTD.
E. I. DU PONT DE NEMOURS & CO.
Japa~ieseAppl. 91192,494 A catalyst for the production of 3-chloropropyltrichlorosilane (CPTCS) from allylchloride and trichlorosilane comprises a tertiary amine, such as quinoline, and a colloidal Pt catalyst. T h e amount of tertiary amine is preferably 0.1-5.5 equivalents with respect to 1 mol of Pt. Allylchloride reduction, a side reaction, is suppressed, so CPTCS is obtained in high yield. It is used as a silane coupling agent.
World Appl. 97129,069A Pentenoic acid or a pentenoate ester, used in preparation ofnylon, etc., is produced by contacting a mixture of pentenoic acid chloride, chlorobutene and a Pd catalyst with H,O or alcohol. The molar ratio of H,O or alcohol : pentenoic acid chloride is < 1.2 and that of chlorobutene : Pd > 10 during a major part of the preparation. Decomposition of the Pd catalyst is avoided and the relatively stable end products can be separated from the reaction mixture by distillation. Almost no reaction of chlorobutene with HzO or alcohol to an undesired by-product occurs.
High Octane Aviation Benzine LENGD. LENNEFrKHIM. RES. PRODN. ASSOC
Russian Patent 1,438,228 High octane aviation benzine is produced by the catalytic reforming of an atmospheric benzine fraction, at 440470°C and elevated pressure, in the presence of a catalyst containing Pt, CL and ALO;. The catalyst additionally contains a synthetic erionite zeolite (I), at a ratio (in wt.%): Pt 0.1-1.0, CL 0.1-1.0, (I) 10-50 with the balance ALO,. The method improves the quality of the product and simplifies technology.
Catalyst for Removing Organic Compounds VORONEZHSINI'EZKAU(:HUR STOCK CO.
Russian Patent 2,072,898 An aluminosilicate carrier in the form of spherical granules is impregnated with a 0.8-2.5 g I ' solution of chloroplatinic acid or I'd chloride at a ratio of solution to carrier of 0.6-0.8: 1 by volume, to an absorption level of 5 100%. The catalyst is then sulfided with H,S and dried. The catalyst has a high mechanical strength, high thermal stability and increased activity, and gives 99-99.55% removal of organics and oxidation products from industrial waste gases.
Preparation of y-Butyrolactone BEIJING CHEM. IND. INST. MIN.
Chiuese Patem 1 , l l 1,167 A catalyst comprises Cu, Zn and Al oxides as a matrix with a surface coating of Pd or Pt. The unreduced catalyst matrix comprises (in wt.%): 20-65 CuO, 20-55 ZnO and 5-30 ALO, and the ratio of Pd or Pt to the matrix is 0.005-0.1. The catalyst size is 5 mm in diameter and 5 mm in length. When used at 280"C, 1 atm and a Hxanhydride molar ratio of 40, the catalyst gives 100% conversion of cis-butandioic anhydride to give y-butyrolactone in 92.7%)yield.
HOMOGENEOUS CATALYSIS Preparation of Hydrogen Peroxide S.P.A. Europeaii Appl. 788,998A H102is prepared from CO, O2and H,O in the presence of a soluble Pd acetate catalyst, an anine or phosphine ligand and H S O Iin an organic solvent, preferably chlorobenzene, such that the solubility of H:O in the solvent is 0.025-0.035%). The process is carried out in cycles with the ligand regenerated and recycled into the reaction. The use of H2 is avoided and yields are improved by the solvent.
ENICHEM
Plariuuui Merals Reo., 1998, 42, (1)
Carbonylation Catalyst DAICEL CHEM. IND. LTD. Japairese Appl. 91173,860 A catalyst for the carbonylation of acetylene or unsaturated olefins, to give (un)saturated organic carboxylate, contains a Pt source, organic phosphine and an organic carboxylic acid. This catalyst has a higher stability, giving higher conversion and yield in liquid phase reactions, for example 99.2% ofpropylene was converted to methyl methacrylate in 92.0% yield.
Preparation of P,y-Uusaturated Compounds MIIXXISHI CHEM. COW. Japanese Appl. 91176,05 1 The preparation of p,y-unsaturated compounds (1) with a skeletal structure derived from a massive conjugated alkadiene, comprises reacting a conjugated alkadiene with an active H-containing compound using a Pd compound and a trivalent P compound. (1) are obtained in high yield and selectivity and are used for plasticisers or aromatics, or are easily converted to olefins for co-monomers.
FUEL CELLS Gas Permeable Electrode AUTOMOBILES CITROEN S.A.
Europeau Appl. 788,174A A gas permeable electrode for membrane fuel cells is produced by pre-impregnating C with a solution of Pt anions or cations, mixing with an ionomer solution and reducing the Pt electrochemically by mounting the electrode as a cathode and conducting electrolysis with an aqueous electrolyte. The electrodes have in situ Pt deposits, where Pt/Pt+C > 20% for a thickness of 10-20 pn with a homogeneous particle size of 2-5 nm, and a percentage of Pt in contact with the ionomer and the C of the order of 100%.
Selective Oxidiser for Fuel Cell Power Plant INT. FUEL CELLS cow. World Appl. 97125,752A An assembly, for selectivelyoxidising hydrocarbon fuel gas and converting CO in a reformed fuel gas to COL, has a gas flow section with Pt catalyst coated passages joined by a common wall to a section containing coolant passages. The flat construction allows the heat exchange per unit volume of the catalyst in intimate contact with the heat exchange surface to be increased so that the volume of the oxidiser can be reduced.
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Electrical Interconnect Device
Formation of Platinum Silicide Plugs
CERAMIC FUEL C E I I S L.TD.
World Appl. 97135,34912 An electrical interconnect device for planar solid oxide fuel cells has a plate-like Cr-containing substrate with fuel gas-flow channels on one side and an oxidationresistant coating on the sides which contact the anode. The outer 0, barrier layer of the coating is 0.5-100 pm thick and comprises one or more of Ni, Pt, Pd, Au, Ir, Rh and Ru, especially Ni.or Pt or their alloys. An electrically conductive metal barrier layer 0.5-100 pm thick comprising Nb, Ta, Ag or their alloys lies between the substrate and the outer 1ayer.The planar fuel cell assembly is also claimed.
1.. G . SEMICON. CO. LTD. U.S. Parent 5,645,887 A PtSi plug is produced by forming an insulating layer on a Si substrate, which has a conductive layer on part of it, patterning to form a contact hole and exposing the conductive layer to air to form a native oxide film. A poly-Si film is formed on the native oxide to completely fill the hole and etched back to expose the insulating layer, forming a plug in the contact hole. A Pt layer is formed on the Si plug and the insulating layer is heat treated to convert the plug into PtSi. T h e remaining Pt is removed. This method is used to form contact plugs of high aspect ratio in LSI devices.
Fuel Cell
Permanent Magnetic Film
(:AI.IFORNIA IKST. O F TECHNOL.
N E C COKP Japanese Appl. 9163,020 A permanent magnetic film on a magnetoresistive head has a closed packed structure of 8-25 wt.% CoCr-Pt alloy, with the Cr-Pt composition being 9-12 wt.%. It is very corrosion proof, and has increased resistance to organic solvent, peeling liquid and developingletching solution. It stabilises the vertical magnetic field, improves the symmetry of the reproduced waveform and avoids the Barkhausen noise effect.
U.S. Puren! 5,656,388 A fuel cell has an electrolyte, a fuel electrocatalysing anode and an 0: electrocatalysing cathode of a temary metal alloy, AB, >X,,where A is one or more rare earth metals; B is one or more of Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Mn, Cd, Hg and Al; X is at least one element E selected so that at least one binary alloy AE or BE has an enthalpy of formation greater than that of the binary alloy La-Sn; and t 0. T h e cathode alloy in hydride form has a good structural integrity and H 1 capacity.
Phosphoric Acid Electrolytic Fuel Cell FUJI ELECTRIC CO. I.TD. Japanese Appl. 91134,728 A fuel cell, for fuel and air electrodes, comprises a porous matrix, impregnated with phosphoric acid and placed between layers of acetylene black supporting a Pt catalyst containing PTFE binder. T h e mixing ratio by wt. of PTFE : C is 0.2-0.8. The lifetime of the cell is increased by suppressing the transfer of phosphoric acid to the fuel electrode.
ELECTRICAL AND ELECTRONIC ENGINEERING Multichip or Hybrid Circuit Module DIEHI. G m
b H & CO Eio-opun Appl. 795,902A This module has a multilayer ceramic substrate on which the dies are positioned with wire bonds at sites with Bi or Ag-Pd metallisation. There is an electrically conductive adhesive layer under each die to which a heating current is injected from a D C or AC power source by a pair of probes in a slotted manipulator. This allows reworking without thermal stress. World Appl. 97131,370A A grain oriented multilayer perpendicular recording medium has layers of common grain structure alternating between a magnetic Co alloy layer < 50 I% thick and a thinner noble metal layer, which includes at least one of Pd and Pt, 2 2.2 A in thickness. The overall atomic concentration of Co is in the range 60-95% and includes a non-homoeeneouslv disDersed maenetic element. Archival data can be stored with a very small distance between adjacent magnetic transitions. DENSITEK C O W .
I
Plarinuiir Metals Rev., 1998, 42, (1)
Japanese Appl. 9164,300 A ferroelectric memory has a lower electrode comprising a Pt film and an electrically conductive oxide film with a perovskite structure on which a ferroelecUic film and an upper electrode are sequentiallyformed. This prevents deterioration of the crystal state of the ferroelectric film and greatly improves its efficiency.
OK1 ELECTRIC IND. C O . I.TD.
Magnetic Recording Medium KAO C O W Japaviese Appl. 9169,44 1 A magnetic recording medium has an amorphous C substrate and a magnetic layer at the surface of the substrate consisting of 6-1 1% Cr, 6-10% Pt, 4-10% B, and the remainder is Co. A high holding force is obtained that corresponds to a high density recording.
Printed Circuit Structure S. SERIZAWA Japanese Appl. 91172,237 A printed circuit structure includes Pd-Ni plated on a Cu foil or a C u plating, formed as a top layer on a foundation layer made of resin ceramics or an alloy, over which Au plating is formed by electroless substitution. The structure offers superior bonding capability, inhibits diffusion and is heatproof.
Piezoelectric Element
Grain Oriented Recording Media
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Ferroelectric Memory Using Platinum Film
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MATSUSHITA DENW SANGYO K.K.
Japanese Appl. 9118 1,369 The manufacture of a reduced size piezoelectric element involves forming a Pt layer 0.1 pm thick on a 80 pm thick polyimide film. A 100 mJ s cm ’ pulse W laser beam is irradiated onto the Pt layer at room temperature to form a PbTiO, thin film on the Pt layer.
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The New Patents abstracts have been prepared from material published by Dement Information Limited.
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