CeO2-supported vanadium oxide catalysts for soot oxidation: the roles of molecular structure and nanometer effect

The nanometer CeO2 powder was prepared by the method of microwave-assisted heating hydrolysis, and the nanometer CeO2- supported or ordinary CeO2-supported vanadia catalysts with different vanadium loadings (atomic ratios: 100V/Ce=0.1, 1, 4, 10, and 20) were prepared by an incipient-wetness impregnation method. Spectroscopic techniques (XRD, FT-IR, Raman and UV-Vis DRS) were utilized to characterize the structures of VOx/CeO2 catalysts. The results showed that the structures of CeO2-supported vanadium oxide catalysts depended on the vanadium loading. Isolated mono-vanadate species were present on the surface of catalysts at low V loading, and poly-vanadate species existed at medium V loading, but CeVO4 crystallites were formed at high V loading (V10 and V20). The catalytic performances of these catalysts for diesel soot oxidation were investigated with temperature-programmed oxidation reaction (TPO). For soot oxidation, the poly-vanadate species were mainly active sites in ordinary CeO2-supported vanadyl catalysts, but nanometer CeO2 was mainly active components in nanometer CeO2-supported vanadium oxide catalysts. Due to the nanometer effect and the good contact between the catalyst and the soot, nanometer CeO2 exhibited a very high catalytic activity for soot combustion.