Effect of Alkaline Earth on Crystal Sizes of ZSM-5 Type Zeolites and Their Catalytic Properties for Alkylation of Toluene with Methanol

摘要

Various ZSM-5 type zeolites containing alkaline earth metals with SiO_2/Al_2O_3 ratio 160 were synthesized by varing the OH~-/SiO_2 ratio in the synthesis mixture. The crystal shape, acidity, steaming durabilities and catalytic properties for the alkylation of toluene with methanol were investigated. Pyridine TPD shoed that the total amount of acid sites is equal to the amount of Al in H-ZSM-5 structure regardless of containing alkaline earth metals. H-ZSM-5 containing alkaline earth metals had the same amount of total acid sites, however it had larger crystal size and amount of weak acid sites than H-ZSM-5 without alkaline earth metals. H-ZSM-5 containing alkaine earth had larger total amount of acid sites, especially weak acid sites after steaming treatment at 973 K than H-ZSM-5 without alkaline earth metals. H-ZSM-5 containing alkaline earth metals had better catalytic alkylation activities of toluene with methanol. H-ZSM-5 containing Mg especially showed superio p-xylene selectivity to equilibrium p-xylene selectivity in xylene products.