高温水蒸气处理对ZnHZSM-5活性中心的影响

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

应用X-射线衍射、能谱表面分析和吡啶吸附红外光谱研究了高温水蒸气处理对HZSM-5和ZnHZSM-5催化剂的影响，并以丙烷芳构化作为探针反应考查了催化活性中心的变化．高温水蒸气处理对分子筛的结晶度影响不大，但水蒸气处理使得分子筛骨架铝脱出，脱出的铝在表面富集，分子筛锌交换位的骨架铝脱出较难，脱铝导致分子筛的酸性减弱．高温水蒸气处理后的HZSM-5和ZnHZSM-5催化剂的丙烷反应活性都降低，在ZnHZSM－5上丙烯的选择性增加，反映了具有脱氢活性的锌的强L酸中心数目相对B酸中心减少较少。

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 asidity, 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.