MODIFICATION OF HZSM-5 BY CVD OF VARIOUS SILICON-COMPOUNDS AND GENERATION OF PARA-SELECTIVITY

The modification of HZSM-5 zeolite was carried out by a method of chem ical vapor deposition of various silicon alkoxides. We thus obtained t he HZSM-5 zeolites with the different pore-opening sizes and with the varied extents of inactivation of acid sites on the external surface. Among the various silicon compounds used in this study, the SiOCH3(C3H 7)(3) was effective in selective inactivation of acid sites on the ext ernal surface of HZSM-5 zeolite without affecting its intracrystalline void space. From the characterization of the modified HZSM-5 zeolites , and its relationship with the shape selectivity, we concluded that t he enhancement of para-selectivity in the methylation of toluene was a scribable more closely to controlling the pore-opening size than to th e inactivation of acid sites on the external surface. (C) 1996 Academi c Press, Inc.