DEALUMINATION OF HEXAGONAL POLYTYPE OF FAUJASITE BY TREATMENTS WITH SILICON TETRACHLORIDE VAPOR

The hexagonal polytype of faujasite with Si/Al ratio of 3.26 is synthesized according to the procedure outlined by Delprato et al. (Zeolites for the Nineties - Recent Research Reports, 8th IZC, Amsterdam, July, 1989, 127). This material is dealuminated with silicon tetrachloride vapour at temperatures between 573 and 823 K to give a series of crystalline materials with framework Si/Al ratios ranging from 4.76 to 26.43. After subsequent washing and ammonium exchange, the solids are extensively characterized using a variety of physicochemical methods. The dealumination with SiCl4 does not produce observable losses in structural integrity. Unit-cell dimensions decrease from a = 17.326 angstrom and c = 28.323 angstrom for the as-synthesized material to a = 17.067 angstrom and c = 27.885 angstrom for the most highly dealuminated sample. Continuous changes in material properties at different degrees of dealumination are observed by Si-29 MASNMR, IR, ammonia temperature-programmed desorption, and Ar adsorption measurements.