Zeotypes

Zeolites are aluminosilicates characterized by a network of silicon and aluminum tetrahedra with the general formula Mx(A102)x(Si02)Y. The M are cations that are necessary to balance the formal negative charge on the aluminum atoms. The tetrahedra are linked to form repeating cavities or channels of well-defined size and shape. Materials with porous structures similar to zeolites but with other atoms in the framework (P, V, Ti, etc.), as a class are referred to as zeotypes. The structure committee of the International Zeolite Association (IZA http //www.iza-online.org/) has assigned, as of July 1st 2007, 176 framework codes (three capital letters) to these materials. These mnemonic codes do not depend on the composition (i.e. the distribution of different atom types) but only describe the three-dimensional labyrinth of framework atoms. 

Zeolite Y, 2 345t, 5 238-239, 11 678, 679 coke formation on, 5 270 for liquid separation adsorption, 1 674 manufacture, 2 359 structure, 1 675 Zeolite ZSM-5, 11 678 Zeolitic cracking catalysts, 16 835 Zeolitic deposits, 16 813 Zeonex, 10 180 Zeotypes... 

Vimont A, Goupil J-M, Lavalley J-C, Daturi M, Surble S, Serre C, Millange F, Ferey, G, Audebrand N. Investigation of acid sites in a zeotypic giant pores chromium(lll) carboxylate, J. Am. Chem. Soc. 2006, 128, 3218-3227. 

With rapid development of zeotypic materials and mesoporous solids and their application in heterogeneous catalysis, HRTEM shows its advantages in distinguishing the ultrastructural features [40, 41], Carbon materials are used as support in catalytic reactions due to some of their specific characteristics and many publications report the TEM investigations on various forms of carbon related materials [42-48],... 

Overall Milton s concept of hydrothermal crystallization of reactive gels has been followed with various additions and modifications for most of the molecular sieve, zeolite, and zeotype materials synthesis since the late 1940s. 

Gonradsson, T., Dadachov, M.S., and Zou, X.D. (2000) Synthesis and structure of (Me3N)6[Ge32064](H20)4.5, a thermally stable novel zeotype with 3D interconnected 12-ring channels. Micropor. Mesopor. Mat., 41, 183-191. 

Cumene was originally produced with SPA- [57], then FAU- or BEA-based catalysts, and most recently MWW. While most industrial processes use MWW-based catalysts [58], Dow and KeUog co-developed a dealuminated MOR based process called 3-DDM [59]. With each new process generation, conversion and selectivity to cumene has increased. These processes and the chemistry behind them are covered in Section 15.4. As the use of zeoHtes for alkylation reactions in industry increased, so did the study of the reaction and how the zeoHte topology affects the mechanism and selectivity to products, so that now many zeotypes are tested for aromatic alkylation as a way of figuring out a new structure s reaction pattern. Therefore, many zeotypes have been used to catalyze aromatic alkylation (Tables 12.9-12.11). 

Processes such as UOP s Isomar process are used to carry out isomerization of C8 aromatic species so that p-xylene can be removed selectively from the mixture of xylenes. The reaction is equilibrium controlled, so a continuous isomerization process is used. As is seen below, both aluminophosphate and aluminosilicate zeotypes are capable of catalyzing the reaction (Table 12.13). 

Values for channel and cavity sizes for various zeolites and zeotypes are listed in Table 7.1. 

Zeolite/zeotype Structure type code No. of tetrahedra in ring Window diameter (pm) Cavity diameter (pm)... 

Other framework structures based on zeolites have also been synthesized which contain atoms other than aluminium and silicon, such as boron, gallium, germanium, and phosphorus, which are tetrahedrally coordinated by oxygen. Such compounds are known as zeotypes. Pure aluminium phosphate, commonly called ALPO, and its derivatives, can take the same structural forms as some of the zeolites such as sodalite (SOD), faujasite (FAU), and chabazite (CHA) (e.g., ALPO-20 is isostructural... 

Catalysis. - Aluminophosphate molecular sieves (A1PO) form a family of synthetic zeotypes, containing many three dimensional framework structures. Metal substituted aluminophosphates (MAPO) have important applications as catalysts and HFEPR has been used to determine the catalytically active sites. Two very detailed papers on various MAPO have been reported recently22,23 using both echo-detected HFEPR at 95 GHz and 3H and 31P ENDOR. 

The development of mesoporous materials with more or less ordered and different connected pore systems has opened new access to large pore high surface area zeotype molecular sieves. These silicate materials could be attractive catalysts and catalyst supports provided that they are stable and can be modified with catalytic active sites [1]. The incorporation of aluminum into framework sites of the walls is necessary for the establishment of Bronsted acidity [2] which is an essential precondition for a variety of catalytic hydrocarbon reactions [3], Furthermore, ion exchange positions allow anchoring of cationic transition metal complexes and catalyst precursors which are attractive redox catalytic systems for fine chemicals [4]. The subject of this paper is the examination of the influence of calcination procedures, of soft hydrothermal treatment and of the Al content on the stability of the framework aluminum in substituted MCM-41. The impact on the Bronsted acidity is studied. 

Related to guanidinium sulfonates are analogous cation phosphonate structures which can adopt either pillared or zeotype structures. Recently novel tubular morphologies have also been discovered for both classes of compound which may have promise for improving porosity in these types of material. At present, like the guanidinium sulfonates, few phosphonates, are really porous and removal of the guest template generally leads to the collapse of the structures.15... 

Zeotype and Mesoporous Solids Chemistry Design, Synthesis and Catalytic Properties... 

Zeolites, ZEOTYPES AND MESOPOROUS SOLIDS SYNTHETIC ASPECTS. 1... 

Bu et al. investigated the role of methyl amine as the organic template in thesynthesis of a series of zeotype germanates. In the absence of the template a two-dimensional layered structure was formed. In contrast, in the presence of methylamine a three-dimensional framework evolved from these sheets.1191... 

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