THE ELECTRONIC MODIFICATION EFFECT OF METAL OXIDE ADDITIVES ON Pt/η-Al_2O_3 CATALYST
Yang Xi-yao, Liu Jia and Pang Li (Department of Chemistry, Beijing University)
The electronic modification effect of various metal oxides on Pt/η-A12O3 catalyst has been studied by TPR, HOT, competitive hydrogenation method and reactions of hydrogenation of benzene and hydrogenolysis of cyclopentane. The relative adsorption coefficients of toluene to benzene (KT/B) determined by competitive hydrogenation method for Pt/η-Al2O3 containing various oxide additives indicate that KT/B values of catalysts containing oxide of Zn, Ni, Sn, W or Cr are larger than that of mono Pt/η-Al2O3, the oxide additives act as electron acceptor and induce an additional electron deficiency of Pt, i. e. Pt becomes more electrophilic. However, KT/B values of catalysts containing oxide of Mo, La, Mg or Cc are smaller than that of Pt/-Al2O3, these additives act as electron donor and alleviate the electrophilic character of Pt.When plotting the KT/B vs the activity of catalysts for hydrogenation of benzene, hydrogenolysis of cyclopentane and dehydroaromatization of hexane, two volcano-shape curves and a valley-shape curve are obtained respectively.From the above facts, it is concluded that the electronic effect of metal oxides upon, the supported Pt catalyst is a universal effect, which modifies significantly the electronic state of Pt, and so alters the catalytic behavior of catalysts.