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

Aromatization of n-hexane and disproportionation of toluene over H-ZSM-5 an d 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 aci dity 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 th e aromatization of n-hexane on Zn-ZSM-5 is probably the formation of carbon ium ions by hydride abstraction with acid sites in zeolite and that Zn spec ies have a decisive role in oligomerization of cracking products and in deh ydrogenation of cyclic intermediates.