Molecular sieve phosphates, synthesis

Szostak R 1998 Synthesis of molecular sieve phosphates Molecular Sieves Science and Technology vol 1, ed H G Karge and J Weitkamp (Berlin Springer) pp 157-85... 

The second most important class of molecular sieves besides the alumo-silicates are without any doubt the alumophosphates and their derivatives containing elements other than aluminum and/or additional elements in the framework. Chapter 6 authored by R. Szostak is a review covering the synthesis of these molecular sieve phosphates. 

In 1982, Union Carbide reported the synthesis of the first phosphate-based molecular sieves (95, 96). This finding would include aluminophosphates (A1P04) and gallophosphates (GaP04) as well as silicoaluminum phosphates (SAPO) and metalloaluminum phosphates [MAPO, M = first-row transition metal (TM)]. The... 

These structures are unique for several reasons. First, they represent three new multidimensional 12-MR systems, which are rare even among zeolites. Second, the amount of framework substitution by metals such as Mn2+ and Mg2+ was unknown prior to this series. Also, the ease of forming both gallium and aluminum phosphates appear to be comparable. Finally, it would appear the charge-matching approach has proven to be a successful strategy for the synthesis of new molecular sieves. It is not clear whether these materials are thermally or hydrothermally stable but they do represent novel pore structures that should impart some unusual properties. 

Gier, T.E., and Smcky, G.D. (1991) Low-temperature synthesis of hydrated zinco(beryllo)-phosphate and arsenate molecular sieves. Nature, 349, 508-510. 

Chen, C. and Jehng, J. (2003) Effect of synthesis pH and H20 molar ratio on the structure and morphology of aluminum phosphate (AlPO-5) molecular sieves. Catal. Lett., 85 (1-2), 73-80. 

Sinha, A.K., Sainkar, S., and Sivas-anker, S. (1999) An improved method for the synthesis of the silicoalumino-phosphate molecular sieves, SAPO-5, SAPO-11 and SAPO-31. Micropor. Mesopor. Mater., 31, 321-331. 

Conditions for A1PQ4-H3 and MCM-1 Synthesis. From previous section it cSh Be concluded that as far as the coordination of A1 is concerned, AlPC -EU is a hybrid between the aluminum phosphate hydrates like variscite and metavariscite and the aluminophosphate molecular sieves. It can be expected that the synthesis conditions under which it crystallizes will also be intermediate between those of hydrates and molecular sieves. Literature together with the present new data seem to confirm this. 

The typical A1P0 synthesis gel contains four components an alumina source, a phosphate source, water, and an organic amine or quaternary ammonium salt. The relative concentrations and, of course, the individual characteristics of these reactants are important factors in the preparation of A1P0<, molecular sieves. One factor is particularly evident, namely, without the organic no A1P0<, molecular sieves are formed. The concept of a template in molecular sieve synthesis is not new. A template is a spec-... 

The synthesis of aluminophosphate molecular sieves in 1980s represents a breakthrough in the development of microporous materials. Since then, much of the worldwide synthetic efforts have been directed toward nonsilicate microporous materials. Many novel framework topologies could be found with phosphates, and many other elements could be incorporated into phosphates to produce additional new framework topologies or new compositions. 

The use of molecular sieves as catalysts or catalyst components for synthesis of intermediates and fine chemical has increased impressively over the last two decades. A large number of reactions has been explored over a growing number of microporous materials. Also the level of imderstanding of the catalytic chemistry and the structure-activity relationships has greatly improved. Since the first review of Venuto and Landis in 1968 [1] and the one of Venuto in 1994 [2] the discovery of medium pore zeolites such as ZSM-5 [3] and of phosphate based molecular sieves [4] had the largest impact on the field. 

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