Structural, redox and acid–base properties of V2O5/CeO2 catalysts

CeO2 supported V2O5 catalysts were prepared by the wetness impregnation technique and their surface structures were characterized by O2 chemisorption, X-ray diffraction (XRD) and Raman spectroscopy (LRS). The surface acidity and basicity were measured by using microcalorimetry and infrared spectroscopy (FTIR) for the adsorption of NH3 and CO2. Temperature programmed reduction (TPR) was employed for the redox properties. In particular, isopropanol probe reactions with and without the presence of O2 were employed to provide the additional information about the surface acidity and redox properties of the catalysts. Variation of loading of V2O5 and calcination temperature brought about the changes of surface structures of dispersed vanadium species, and hence the surface acidic and redox properties. Structural characterizations indicated that V2O5 can be well dispersed on the surface of CeO2. The monolayer dispersion capacity was found to be about 8 V/nm2, corresponding to about 10% V2O5 by weight in a V2O5/CeO2 sample with the surface area of 80 m2/g. Vanadium species in the catalysts (673 K calcined) with loading lower than 10% were highly dispersed and exhibited strong surface acidity and redox ability, while higher loading resulted in the formation of significant amount of surface crystalline V2O5, which showed fairly strong surface acidity and significantly weakened redox ability. Calcination of a 10% V2O5/CeO2 at 873 K resulted in the formation of mainly CeVO4 on the surface, which showed low surface acidity and redox ability. The probe reaction seemed to suggest that the calcination at higher temperature might cause the decrease of surface acidity more than redox ability. Thus, the 10% V2O5/CeO2 catalyst calcined at 873 K exhibited much higher selectivity to benzaldehyde as compared to other V2O5/CeO2 catalysts studied in this work, although its activity for the conversion of toluene was relatively low.