Raman and X-ray photoelectron spectroscopy study of CeO2-ZrO2 and V2O5/CeO2-ZrO2 catalysts

The evolution and physicochemical characteristics of CeO2-ZrO2 and VO5/CeO2-ZrO2 samples under the influence of thermal treatments from 773 to 1073 K were investigated using X-ray diffraction (XRD), BET surface area, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The CeO2-ZrO2 mixed oxide was synthesized by a coprecipitation method, and a nominal 12 wt % V2O5 was deposited over the calcined support (773 K) by a wet impregnation technique. The X-ray powder diffraction analysis suggests formation of a Ceo(0.75)Zr(0.25)O(2) cubic phase at 773 K. With increasing calcination temperature, better crystallization of this phase and incorporation of more zirconium into the ceria lattice were noted. The mean crystallite size and a cell parameter values obtained from XRD measurements strongly support this observation. The results further suggest that impregnation of vanadium oxide over the CeO2-ZrO2 surface accelerates the crystallization of Ce0.75Zr0.25O2 and incorporation of more zirconium into the ceria lattice, thereby facilitating appearance of zirconia-rich phases. A preferential formation of CeVO4 compound was also noted at higher calcination temperatures. The XRD and Raman results, in particular, provide direct evidence about the formation of CeVO4. The XPS measurements reveal stabilization of Ce(III) at higher calcination temperatures and no significant changes in the oxidation states of Zr(IV) and V(V).