Effect of High Temperature Water Steaming on the Active Centers of ZnHZSM-5

Abstract

The effects of high temperature water steaming (HTWS) on the structure of HZSM-5 and ZnHZSM-5 catalysts have been investigated using XRD, XPS and IR spectrum of adsorbed pyridine, and the aromatization of propane has been tested as a probe reaction to show the change of catalytic performance. The result indicate that the treatment of HTWS nearly has no significant effect on the crystallinity of zeolite catalysts, but it lead to the dealumination of zeolite framework and the migration of zinc ions departing from the cation positions and results in the enrichment of aluminum and zinc content on the outer surface of zeolite crystallites and the decrease of catalyst acidity, and comparing the variation of Si/Al with Zn/Si and Zn/Al, it is shown that the framework aluminum species with zinc counterions are more difficult to detach from the framework than those with proton counterions. The variation of the reaction activity and selectivity of propane aromatization also verifies that the active centers of B and Zn-L acids are diminished differently depending on the treatment of HTWS processing.