Dealumination of hexagonal polytype of faujasite by treatments with silicon tetrachloride vapour

Abstract

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 Å and c= 28.323 Å for the as-synthesized material to a= 17.067 Å and c= 27.885 Å for the most highly dealuminated sample. Continuous changes in material properties at different degrees of dealumination are observed by ²⁹Si MASNMR, IR, ammonia temperature-programmed desorption, and Ar adsorption measurements.