EFFECTS OF IN-SITU CHEMICAL-VAPOR-DEPOSITION USING TETRAETHOXYSILANE ON THE CATALYTIC AND SORPTION PROPERTIES OF ZSM-5

The external surface of HZSM-5 crystals was gradually modified by in-s itu CVD of tetraethoxysilane. Using the particular procedures describe d in the paper, it was shown from probe reactions in combination with sorption studies that the external surface was deactivated and the por e-opening size was reduced while the intracrystalline pore space remai ned unmodified. The positive effect of the CVD treatment procedure on the shape selective properties of HZSM-5 was demonstrated by an enhanc ement in p-selectivity during toluene disproportionation. The paper di scusses the relation between the effects of the CVD treatment procedur e on catalytic properties, sorption properties and structural properti es and conclusions are made on the use of the conversion of 1,2,4-trim ethylbenzene, 1,3,5-triisopropylbenzene, toluene and n-hexane, respect ively, to probe the effects of external surface modifications on prope rties of ZSM-5. (C) 1998 Elsevier Science B.V. All rights reserved.