SHAPE-SELECTIVITY OVER HZSM-5 MODIFIED BY CHEMICAL VAPOR-DEPOSITION OF SILICON ALKOXIDE

Alkylation of toluene with methanol and toluene disproportionation have been carried out over HZSM-5 zeolites modified by chemical vapor deposition of silicon alkoxide. As the silica amount increased, the selectivity to m- and o-xylenes decreased, whereas that to p-xylene increased. The fraction of the para isomer in xylenes increased to more than 98%. From adsorption measurements and test reactions, it was found that this modification resulted in the narrowing of the pore-opening size and the inactivation of the external surface. The high para-selectivity was caused primarily by the narrowing of the pore-opening size. © 1991.