Modification of the acidic properties by introduction of zinc into ZSM-5 zeolites

Aromatization ofn-hexane and disproportionation of toluene over H-ZSM-5 and Zn-ZSM-5 prepared by ion-exchange with aqueous solution has been studied. Introduction of zinc into ZSM-5 does not significantly affect the total acidity determined by TPDA, but causes redistribution in the strength and type of acid sites. From the results it was concluded that the first step in the aromatization ofn-hexane on Zn-ZSM-5 is probably the formation of carbonium ions by hydride abstraction with acid sites in zeolite and that Zn species have a decisive role in oligomerization of cracking products and in dehydrogenation of cyclic intermediates.