Structural Characterization of CeO2−TiO2 and V2O5/CeO2−TiO2 Catalysts by Raman and XPS Techniques

Structural characteristics of ceria−titania and vanadia/ceria−titania mixed oxides have been investigated using X-ray powder diffraction (XRD), Raman spectroscopy (RS), and X-ray photoelectron spectroscopy (XPS) techniques. The (1:1 mole ratio) mixed oxide was obtained by a coprecipitation method, and a nominal 5 wt % V 2 O 5 was deposited over its surface by a wet impregnation technique. Both of the materials were then subjected to thermal treatments from 773 to 1073 K and were characterized by the above-mentioned techniques. The XRD results suggest that the CeO 2 −TiO 2 mixed oxide calcined at 773 K primarily consists of poorly crystalline CeO 2 and TiO 2 -anatase phases and that a better crystallization of these oxides occurs with increasing calcination temperature. The “ a ” cell-parameter values suggest some incorporation of titanium into the ceria lattice. Impregnation of vanadia on ceria−titania enhances the crystallization of CeO 2 and TiO 2 oxides. However, no crystalline V 2 O 5 could be observed from XRD and RS measurements. Furthermore, the dispersed molecular vanadium oxide (polyvanadate), evidenced by Raman measurements, interacts preferentially with the CeO 2 portion of the mixed oxides and forms the CeVO 4 compound at higher calcination temperatures. The XRD and RS results provide direct evidence about the formation of CeVO 4 . The XPS electron-binding energies indicate that ceria, titania, and vanadia are mainly in their highest oxidation states, Ce(IV), Ti(IV), and V(V). The formation of Ce(III) has also been noticed in both CeO 2 −TiO 2 and V 2 O 5 /CeO 2 −TiO 2 samples at all temperatures.