ALKYLATION OF TOLUENE OVER DOUBLE STRUCTURE ZSM-5 TYPE CATALYSTS COVERED WITH A SILICALITE SHELL

Zeolite catalysts, having layered structure of ZSM-5 or borosilicate core covered with a silicalite shell, were prepared by hydrothermal crystallization of silicalite in the presence of ZSM-5 or borosilicate seeds. Characteristics of the prepared catalysts were examined by X-ray diffraction, scanning electron microscopy and temperature-programmed desorption. Comparison of these double-structured catalysts to ZSM-5 type catalysts, showed that they exhibited considerably higher para-selectivity in toluene alkylation reactions, but had slightly lower activity. The former showed higher para-selectivity at the same conversion level. This result suggests that para-selectivity could be enhanced by selectively inactivating the external acid sites without changing the pore mouth size.