Oxidative methylation of toluene with methane catalyzed by cesium modified molecular sieves

摘要

Cesium exhanged zeolites (X, Y, and ZSM-5) and cesimum impregnated molecular sieve AlPO_4-5 were studied as catalysts for oxidative methylation of toluene with methane. The effects of structure and basicity were examined. XRD analysis indicated that in the exchanged zeolites, cesium was finely dispersed while in the impregnated molecular sieve a CsCl phase was obtined. IR spectroscop was more informative than XRD analysis as regards the crystallinity of the catalysts after modification with cesium. The most appropriate structure for the best selectivity and yield of ethylbenzene+styrene was found to be that of CsAlPO_4-5. A uniform distribution of the CsCl phase in accessible sites of the crystal lattice of CsAlPO_4-5 Was assumed. It was established that the best catalyst CsAlPO_4-5 possessed weak basic sites. The performance of the basic sites was related both to the crystallgraphic structure and to cesium location.