Transformation of m-Xylene over Al-Pillared Clays and Ultrastable Zeolite Y

Abstract

The reaction of m-xylene has been carried out at 623 K over Al-pillared beidellite and montmorillonite, and over ultrastable zeolite Y (USY) as a reference catalyst. These microporous acidic solids exhibit similar open porosities and, therefore, the activity toward disproportionation and/or isomerization is not primarily ruled by geometrical limitations but merely reflects the relative amount and strength of the acid sites, strong Brønsted acid sites being required for disproportionation and weaker ones for isomerization. in terms of overall conversion and disproportionation selectivity, USY is more active than the pillared clays. This is due to a higher content of strong acid sites and to the greater micropore volume of USY. Al-pillared beidellite is more active than Al-pillared montmorillonite, which is interpreted in terms of framework substitution differences between the two clays. The OH/Al molar ratio of the starting pillaring solution does not confer to the pillared materials any significant effect on their catalytic performances. Deactivation is observed for all the catalysts, and there is some evidence that the stronger sites would deactivate first.