Toluene methylation on AlPO4-Al2O3 catalysts (5–15 wt.% Al2O3)

Abstract

The alkylation of toluene with methanol over AlPO4-Al2O3 (5–15 wt.% Al2O3) catalysts produces a mixture of xylenes (XYL) although trimethylbenzenes (TMB) were also found. The TMB selectivity increased with temperature at the expense of XYL selectivity. Isomer distribution was approximately 48, 24 and 27 mol% foro-, m- andp-XYL, and 74, 26 and 0 mol% for 1,2,3-, 1,2,4- and 1,3,5-TMB, both quite different from the equilibrium isomer composition. The catalytic activity increased with alumina content, however, it decreased on increasing the calcination temperature in the 923–1273 K range. Good correlations between catalytic activity and the increase in acidic properties with Al2O3 loading (as determined by base chemisorption, in the gas phase,versus pyridine and 2,6-dimethylpyridine) have been obtained.