Side-chain alkylation of toluene with methanol over alkali-exchanged zeolites X, Y, L, and beta

摘要

Alkali-exchanged zeolites (X, Y, L, and beta) and alkali-impregnated mesoporous alumina were studied as catalysts for toluene alkylation with methanol, The effects of zeolite basicity; zeolite particle size, and port: dimensionality were examined. At 680-690 K and atmospheric pressure,highly basic, alkali-exchanged zeolites X and Y were active for toluene alkylation but primarily decomposed methanol to carbon monoxide. Cesium-exchanged zeolites L, and beta were also active alkylation catalysts but required higher temperatures to attain similar aromatic yields. More importantly, very little carbon monoxide was produced over the L and beta catalysts. Reactivity results for a ball-milled Y zeolite suggested that variations in particle size did not account fur the observed differences in methanol decomposition over the catalysts. Infrared spectroscopy and thermogravimetric analysis indicated that alkali-exchanged X and Y zeolites adsorbed orders of magnitude greater amounts of CO2 than CsL and Cs beta zeolites. Apparently, zeolites with low base site densities and appropriate base strengths selectively alkylate toluene without decomposing methanol to carbon monoxide. The observed activities of L, beta, X, and Y demonstrate that zeolites with one-, two-, and three-dimensional pore networks catalyze side-chain alkylation, Mesoporous alumina modified with cesium and boron was inactive for toluene alkylation but decomposed methanol to carbon monoxide. The inactivity of a basic, mesoporous alumina for conversion of toluene suggests that physical constraints and proximity of acid/base sites within molecular sieve environments may facilitate the side-chain alkylation reaction. (C) 1998 Academic Press. [References: 37]