The First High Specific Surface Area, Pillared, Layered Phosphate with ...

J. CHEM. SOC., CHEM. COMMUN.,

751

1989

The First High Specific Surface Area, Pillared, Layered Phosphate with a Narrow Pore Size Distribution P. Olivera-Pastor,*a A. Jimenez-Lopez,a P. Maireles-Torres," E. Rodriguez-Castellon,a A. A. G. Tomlinson,*b and L. Alagnab a b

Departamento de Quimica Inorganica, Cristalografia y Mineralogia, Universidad de Malaga, 29071 Malaga, Spain I.T.S.E., Area della Ricerca di Roma, C.N.R., C.P. 10 Monterotondo Staz., 00016 Rome, Italy

[A11304(OH)24(0H2)12]7+ has been intercalated under mild conditions into a-tin phosphate monohydrate to give a-Sn{ [A11304(0H)~4(0H)2)12]o.14H(P04)2~nH20} ('AIl3SnP'); calcination of 'AIl3SnP' at 400 "C gives rise to an aluminium oxide-pillared material with a BET surface area of 228 m2 g-1 and a very narrow pore-size distribution centred at a radius of 22 p\.

Insertion of large cations into smectite clays can produce expanded porous materials.' Such 'pillaring' of layered aluminosilicates has given rise to many attempts to prepare new high surface area materials. Such attempts have involved the Keggin-like polyoxocation [A113O4(OH)24(OH2)1*l7+as the pillar, because calcination would be expected to give rise to an aluminium oxide pillar cross-linking to the phosphate sheets. Unfortunately, such cross-linked porous clays have non-accessible pores. We now report that this aluminium oligomer can be inserted into layered phosphates, giving rise to the first pillared phosphate with a high specific surface area. An aqueous solution of n-propylamine (PrnA) was contacted with a-Sn(HP04)2.H20for 1 day (25 "C; ultrasonic bath; I 0 [a-SnP] : [PrnA] = 1: 1). The colloidal suspension obtained is 0" very stable (months, as for the a-ZrP analogue).4 (NMe4)Cl m equivalent to 10 times the cationic exchange capacity (c.e.c.) 3 0was added to this suspension. After contact for 1 day, the half-exchanged material a-Sn(NMe4)o.9-l.oH(P04)2.H~Ot E c

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2.0 4.0 6.0 8.0 10.0 12.0 meqlAI130~(OH)~~(OH2)1~]~* added/g NMeLSnP

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t The compositions of all the materials reported have been confirmed by chemical analysis and thermogravimetry.

Figure 1. Uptake of [A11304(OH)24(OH2)12]7+by a-Sn(NMe4)o.el.oH(P04)2H20, The arrow indicates the material used to obtain 'Al&P.'

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Figure 3. Exchange of divalent transition metal ions into the pores formed after calcination of ‘A113SnP’at 400 “C.

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meso-pores. In contrast, ‘AlI3SnP’(400 “C) shows a relatively high specific surface area, 228 m2 g-1 and a very narrow pore-size distribution, most pores being centred at a radius of 22 8, (Figure 2). Moreover, ‘AlI3SnP’ (400°C) retains ion-exchange characteristics (Figure 3), Co2+ and Ni2+ being taken up to virtually theoretical maximum c.e.c. (2.5 mequiv. 14g-l), based on the empirical formulation a-Sn[A113016]o. (HP04)20nH20 (n = 1,2). Cu2+ is taken up in a greater amount than the c.e.c. (4.1 mequiv. g-1). This points to either cation-exchange occurring at the pillar for Cu2+ as well as at the pendant P-OH groups lying within the cavity,6 or Cu2+ forming &(OH)+ (in agreement with the higher hydrolysis constant for Cu2+)7, which is the species that exchanges. Formation of stable colloidal suspensions of “Me4] exchanged a-tin phosphate precursor also provides a general route to other polyoxocation-pillared materials { e.g. with [Cr3(OH)2(OAc)6]+}8,and other layered phosphates such as the a-ZrP analogue, which give a similar uptake isotherm with chlorohydrol. Using such simple methods the road is now open for size-engineering of pores in such materials. We thank the E.E.C. Euram Programme (Contract No. MAlE/0027/I) and C.A.I.C.Y.T. (Project PB861244) for financial support. +-

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Figure 2. (A); Adsorption-desorption curves (B.E.T. method; N2). (B); Pore-size distribution of ‘Al&nP’ calcined at 400 “C.

Received, 23rd November 1988; Com. 8104643C

(interlayer distance dOo2= 17.5 A) was separated by highspeed centrifugation, washed well and air-dried. It was re-suspended in aliquots of [A11304(OH)24(OH2)12I7+, prepared as in ref. 5; (pH 4.4; 25 “C; 1 day). The products were filtered off, separated by centrifugation, washed and dried (P205). The uptake isotherm of Figure 1shows that maximum uptake corresponds to the formula, a-Sn{ [All3O4(OH)24(OH2)12]0.14H(P04)2.nH20} (‘A113SnP’) (do02 = 19.27 A;no organic matter present). Calcination of this material at various temperatures shows that interlayer collapse occurs at >500 “C, but that a layered structure (dOo2= 13.5 A) is still present at 400 “C. a-Sn(HP04)2.H20itself is a non-porous solid with a low specific surface area [ l l m2 8-1; BET(N2)I and high ionexchange capacity, ‘Al13SnP’possesses a specific surface area of 85 m2 g-1 with a wide distribution of micro- and

References 1 R. M. Barrer, J . Chem. S O C . ,1955, 434; J . Inclusion Phenomena, 1986, 4, 109. 2 D. E. W. Vaughan, Catal. Today, 1988, 2 , 187. 3 E. P. Giannelis, E. G. Rishtor, and T. J. Pinnavaia, J. Am. Chem. SOC., 1988, 110, 3880. 4 G. Alberti, M. Casciola, and U. Costantino, J . Colloid Interface Sci., 1985, 107, 256. 5 M. Tokarz and J. Shabtai, Clays and Clay Minerals, 1985, 33, 89. 6 C. Ferragina, M. A. Massucci, P. Patrono, A. La Ginestra, and A. A. G. Tomlinson, J . Chem. SOC., Dalton Trans., 1988, 851. 7 C. Baess and F. Mesmer, ‘The Hydrolysis of Cations,’ Wiley Interscience, New York, 1976. 8 E. Rodriguez-Castellon, A. Jimenez-Lopez, P. Olivera-Pastor, and A . A. G. Tomlinson, 5th Internat. Symp. Inclusion Phenoma and Molecular Recognition, Orange Beach, Alabama (USA), Sept. 18-23rd, 1988, Abstracts, D13.