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 % V2O5 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 CeO2−TiO2 mixed oxide calcined at 773 K primarily consists of poorly crystalline CeO2 and TiO2-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 CeO2 and TiO2 oxides. However, no crystalline V2O5 could be observed from XRD and RS measurements. Furthermore, the dispersed molecular vanadium oxide (polyvanadate), evidenced by Raman measurements, interacts preferentially with the CeO2 portion of the mixed oxides and forms the CeVO4 compound at higher calcination temperatures. The XRD and RS results provide direct evidence about the formation of CeVO4. 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 CeO2−TiO2 and V2O5/CeO2−TiO2 samples at all temperatures.

Microstructure evolution of ceria-based mixed oxides CeO2−MO2 (M = Si4+, Ti4+, and Zr4+) after thermal treatments in the temperature range of 773−1073 K were investigated by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and other techniques. The CeO2−SiO2 was synthesized by a deposition precipitation method, and a coprecipitation procedure was adopted to make CeO2−TiO2 and CeO2−ZrO2 binary oxides. The XRD measurements revealed the presence of crystalline cubic CeO2 on the surface of SiO2 in CeO2−SiO2, CeO2 and TiO2 (anatase) in CeO2−TiO2, and Ce0.75Zr0.25O2 and Ce0.6Zr0.4O2 phases in CeO2−ZrO2 samples. The crystallinity of these phases increased as the calcination temperature increased. Estimations of the cell parameter a indicated an expansion of the CeO2 lattice in the case of CeO2−TiO2 samples, whereas a contraction was noted in the case of CeO2−ZrO2. Some incorporation of Si4+ ions into the CeO2 lattice was noted at higher calcination temperatures for the CeO2−SiO2 samples. Raman measurements revealed the presence of oxygen vacancies, lattice defects, and the displacement of oxide ions from their normal lattice positions in the case of the CeO2−TiO2 and CeO2−ZrO2 samples. The XPS studies revealed the presence of silica, titania, and zirconia in their highest oxidation statesSi4+, Ti4+, and Zr4+at the surface of the materials. Cerium is present in both Ce4+ and Ce3+ oxidation states, but in different proportions, depending on the mixed-oxide system and the calcination temperature used.

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Structural characteristics of nanosized ceria-silica, ceria-titania, and ceria-zirconia mixed oxide catalysts have been investigated using X-ray diffraction (XRD), Raman spectroscopy, BET surface area, thermogravimetry, and high-resolution transmission electron microscopy (HREM). The effect of support oxides on the crystal modification of ceria cubic lattice was mainly focused. The investigated oxides were obtained by soft chemical routes with ultrahighly dilute solutions and were subjected to thermal treatments from 773 to 1073 K. The XRD results suggest that the CeO(2)-SiO(2) sample primarily consists of nanocrystalline CeO(2) on the amorphous SiO(2) surface. Both crystalline CeO(2) and TiO(2) anatase phases were noted in the case of CeO(2)-TiO(2) sample. Formation of cubic Ce(0.75)Zr(0.25)O(2) and Ce(0.6)Zr(0.4)O(2) (at 1073 K) were observed in the case of the CeO(2)-ZrO(2) sample. Raman measurements disclose the fluorite structure of ceria and the presence of oxygen vacancies/Ce(3+). The HREM results reveal well-dispersed CeO(2) nanocrystals over the amorphous SiO(2) matrix in the cases of CeO(2)-SiO(2), isolated CeO(2), and TiO(2) (anatase) nanocrystals, some overlapping regions in the case of CeO(2)-TiO(2), and nanosized CeO(2) and Ce-Zr oxides in the case of CeO(2)-ZrO(2) sample. The exact structural features of these crystals as determined by digital diffraction analysis of HREM experimental images reveal that the CeO(2) is mainly in cubic fluorite geometry. The oxygen storage capacity (OSC) as determined by thermogravimetry reveals that the OSC of the mixed oxide systems is more than that of pure CeO(2) and is system dependent.

The evolution and physicochemical characteristics of CeO2−ZrO2 and V2O5/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 Ce0.75Zr0.25O2 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).