The Alkylation of Mononuclear Aromatic Hydrocarbons and Related Reactions over H-ZSM-5 Catalysts Modified with Lanthanum and Cerium Oxides

摘要

The ethylation of ethylbenzene and the disproportionation of toluene were examined over H-ZSM-5 impregnated with lanthanum and cerium oxides. The selectivities for p-diethylbenzene and p-xylene were improved in both reactions by the impregnation of these oxides: lanthanum modification was more effective than cerium modification. The cracking of 1, 3, 5-triisopropylbenzene was effectively deactivated by the impregnation with both oxides, whereas the activity for the cracking of cumene was maintained over modified H-ZSM-5 catalysts. Adsorption of o-xylene was retarded significantly by lanthanum modification, whereas the adsorption to cerium modified H-ZSM-5 was in almost the same level as unmodified H-ZSM-5 although the rate of adsorption decreased by the modification. From these results, the improvement of the selectivities of p-isomers in both the ethylation of ethylbenzene and the disproportionation of toluene is due to the retardation of the isomerization of p-isomers at the external acid sites. The improvement of p-selectivity for H-ZSM-5 modified with lanthanum oxide is also due to the reactant selectivity by preferential diffusion of p-isomers from pores narrowed by the modification.