Quantitative spectroscopic characterization of surface metal oxide catalytic active sites.

摘要

A quantitative spectroscopic method was successfully developed by the combination of Raman spectroscopy (both UV and Visible excitation) and UV/Vis Diffuse Reflectance Spectroscopy (DRS). This method has the potential ability to quantitatively characterize the structure of surface species and intermediates, as well as reaction mechanism of supported molybdena and vanadia catalysts in real time and under various conditions (ambient, dehydrated and reaction condition). It was found that the edge energy values of molybdena and vanadia coordination are LIEANERLY degree with the degree of polymerization, this linear relationship could be used to quantitatively determine surface structure of metal oxide. In this approach, for the first time, the surface concentration of monomeric/polymeric VO4 species on supported vanadia catalysts can be measured; and the turnover frequency of monomic/polymeric VO4 on propane oxidative dehydration can be separately determined. The results concluded V-O-support bond is the active site for the propane oxidative dehydration. In this approach, for the first time, the surface structure of Mo/HZSM5 will be assigned as isolated MoO4 and the surface Al-(MoO 4)3 is the active site for methane activation.