ROLE OF 18-CROWN-6 AND 15-CROWN-5 ETHERS IN THE CRYSTALLIZATION OF POLYTYPE FAUJASITE ZEOLITES

Phases obtained during crystallization of the cubic and the hexagonal end-member of the family of faujasite polytype zeolites and of their i ntergrowths from aluminosilicate hydrogels containing 15-crown-5 ether , 18-crown-6 ether, or a mixture of these ethers were characterized by XRD, IR, SEM, Si-29 and C-13 MAS NMR, TGA, and nitrogen. adsorption. The siting of crown ethers in the intracrystalline voids of the zeolit es is derived from TGA and nitrogen adsorption data. The EMT content o f FAU/EMT intergrowths is determined by multiphase Rietveld refinement of XRD patterns. Correlations between gel composition, crystallizatio n kinetics, and EMT content of end products are established. A molecul ar model for crystallization consistent with the observed correlations is proposed.