Templates in zeolites

Quaternary ammonium bromides and hydroxides (quats) are applied as templates in the synthesis of zeolites with relatively high Si/Al ratio. Examples will be given of the use of mon-, di-, poly- and associated quats as templates in zeolite growth. Templated zeolites of the MFI-type can be grown in a lateral or in an axial way onto metal supports, providing promising composite systems, for separation and catalysis, respectively. 

Synthesis of silica-based materials with controlled skeleton structures, such as zeolites, requires controlling the structure of oligomeric silicate species at the first reaction step. Organic quaternary ammonium ions, which are known as organic templates in zeolite synthesis (1 ), have a role in making up the specific structures of silicate anions, whereas silicate anions randomly polymerize in aqueous solutions containing alkali metal ions, resulting in the presence of silicate anions with different structures. 

The role of organic templates in zeolite synthesis has been studied extensively, but no general principles have been delineated. 

The effect of the location of framework negative charge on the ordering of templates in zeolite IFR... 

P-ll - Isodimorphism of templates in zeolites. New crystal chemistry of analcime and its analogues... 

An example of tme templating in zeolite synthesis is the preparation of the MFl-type materials mentioned above, for example, ZSM-5 (with Si/Al ratio varying... 

The first inverse of the ship-in-bottle synthesis, in which the zeolite cage is constructed around a porphyrin template, was reported by Li and Zhan. " The Fe(II) and Mn(II) derivatives of tetra(Af,A, Af-trimethylanilinium)porphyrin and H2(TMPyP) were used as cationic templates in zeolite hydrothermal synthesis. Attempts to incorporate an anionic porphyrin species, metallo-tetra(4-sulfunatophenyl)por-phyrin, were unsuccessful and trials with neutral TPP species resulted in trace encapsulation. High activity for the catalytic oxidation of cyclohexene by terf-butyl hydroperoxide was reported. 

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