Toluene methylation on Al13- and GaAl12-pillared clay catalysts

The catalytic activity and selectivity of montmorillonite pillared with Al- 13 and GaAl12 polyoxycations have been investigated at temperatures between 573 K and 673 K for the gas-phase microcatalytic alkylation of toluene wit h methanol. A mixture of xylenes (XYs) was obtained as the main reaction pr oducts: 69% and 74% of xylenes for the Al- and GaAl-PILC catalysts, respect ively, at 573 K. Trimethylbenzenes (1,2,4- and 1,2,3-isomers) were also fou nd (31% and 26% for the Al and GaAl catalysts, respectively, at 573 K). The XY-isomer distribution followed the order o>p>m. The influence of the toluene concentration in methanol (2.5; 1.0; 0.5 M) up on the conversion of toluene and the selectivities of the products were als o investigated. An increase in toluene molarity produced a decrease in tolu ene conversion and an increase in xylene selectivity for both the Al and Ga Al catalysts. A good correlation was obtained between catalytic activity and increase in acid sites, as determined by pyridine and dimethylpyridine chemisorption in the gas-phase. (C) 1999 Elsevier Science B.V. All rights reserved.