CHARACTERISTICS,STATES AND REACTIVITY OF DEHYDROCYCLIZATION ACTIVE CENTER OVER Pt-Al_2O_3 CATALYSTS
Pan Yun, Yang Xi-yao and Pang Li (Department of Chemistry, Peking University)
Two different types of dehydrocyclization (DHC) active site, i. e. high temperature active site and low temperature active site, over Pt-Al2O3 catalyst were evidenced by temperature programmed surface reaction method. By H2SO4 solution extraction, it was proved that there existed soluble Pt (i.e. unreduced Pt ions) in the high temperature reduced Pt-Al2O3,the relative amount of soluble Pt increased with decreasing the Pt content of catalyst. High temperature active site and low temperature active site were concerned with soluble Pt and metallic Pt respectively, the former was consisted of ionic and super dispersed (or isolated) atomic Pt, and the latter was consisted of three dimensional dispersed metallic Pt. Low temperature active site was favourable to the hydrogenolysis, but strongly inhibited the DHC. High temperature active site was unfavourable to the hydrogenolysis, its hydrogenolysis behavior showed little effect on DHC.