Catalytic Effect of Configuration Structures of Transition Metal Ions in Catalysts with Highly Dispersed and Isolated Active Sites on the Selective Oxidation of Propane

Abstract

The catalytic performances of the potassium-modified silica-supported catalysts with highly dispersed and isolated active sites containing a tiny amount of transition metal oxide(i.e.,K-M/SiO2(n(K)∶ n(M)∶n(Si)=10∶ 1∶ 1000);M=V,Cr,Mn,Fe,Co,Ni,Cu,Zn) for the selective oxidation of propane were evaluated.The structures and physico-chemical properties of these catalysts were characterized by means of UV-Raman,CO2-TPD.The relationships among the catalytic performances of this series of catalysts for the selective oxidation of propane and their configuration structures of the transition metal cations were studied.The results indicate that the configuration structures of transition metal cations have large effect on the catalytic performances of the catalysts for the selective oxidation of propane.The stable cation structures with d-orbitals,which are fully occupied or empty,are good for the selective oxygenation of propane.But the cations,which have the relatively unstable d-electron structures with mixed valences,are good for the deep oxidation of propane.This relation between the cation structures of highly dispersed and isolated active sites of the catalysts and their catalytic performances is very similar to that found in the selective oxidation of ethane,which further demonstrates that the configuration structures of transition metal cations in the catalysts with highly dispersed and isolated active sites is the most important controlling factor to affect the catalytic performances of this kind of catalysts for the selective oxidation of low alkanes.