Surface Characterization of CeO₂/SiO₂ and V₂O₅/CeO₂/SiO₂ Catalysts by Raman, XPS, and Other Techniques

X-ray diffraction, Raman, and X-ray photoelectron spectroscopy were utilized to characterize CeO 2 /SiO 2 supports and V 2 O 5 /CeO 2 /SiO 2 catalysts calcined at different temperatures from 773 to 1073 K. The CeO 2 /SiO 2 support was obtained by an aqueous deposition precipitation method, and vanadium oxide was applied to the calcined support (773 K) by using a wet impregnation technique. The XRD and Raman results suggest that the CeO 2 /SiO 2 carrier is thermally quite stable up to 1073 K calcination temperature and primarily consists of a CeO 2 overlayer on the SiO 2 substrate. The CeO 2 /SiO 2 support also accommodates a layer of vanadia in a highly dispersed state on its surface. In particular, no crystalline V 2 O 5 was observed. The O 1s, Si 2p, Ce 3d, and V 2p core level photoelectron peaks of CeO 2 /SiO 2 and V 2 O 5 /CeO 2 /SiO 2 are sensitive to the calcination temperature. The XPS line shapes and the corresponding binding energies indicate that the dispersed vanadium oxide interacts selectively with the ceria portion of the CeO 2 /SiO 2 carrier and readily forms CeVO 4 . The XRD and Raman techniques, in particular, provide direct evidence about the formation of CeVO 4 . The V/Ce and V/Si atomic ratios, as determined by XPS measurements, reveal that vanadia is mainly confined to ceria at all calcination temperatures. No significant changes in the oxidation states of V(V) and Si(IV) are noted with increasing calcination temperature. However, in the case of cerium oxide stabilization of Ce(III) was observed at higher calcination temperatures.