Raman and X-ray Photoelectron Spectroscopy Study of CeO₂−ZrO₂ and V₂O₅/CeO₂−ZrO₂ Catalysts

The evolution and physicochemical characteristics of CeO 2 −ZrO 2 and V 2 O 5 /CeO 2 −ZrO 2 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 CeO 2 −ZrO 2 mixed oxide was synthesized by a coprecipitation method, and a nominal 12 wt % V 2 O 5 was deposited over the calcined support (773 K) by a wet impregnation technique. The X-ray powder diffraction analysis suggests formation of a Ce 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 CeO 2 −ZrO 2 surface accelerates the crystallization of Ce 0.75 Zr 0.25 O 2 and incorporation of more zirconium into the ceria lattice, thereby facilitating appearance of zirconia-rich phases. A preferential formation of CeVO 4 compound was also noted at higher calcination temperatures. The XRD and Raman results, in particular, provide direct evidence about the formation of CeVO 4 . 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).