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

Abstract

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.

Sol–Gel Synthesis of Tunable Cerium Titanate Materials

“…[18] This metastable phase could be related to a CeO 2 -TiO 2 mixed oxide with 1:1 atomic ratio, which has been investigated by Reddy et al by various techniques. [19,20] The optical features of cerium makes it a good candidate for colouring applications since the lowest Ce 3+ 4f 1 5d 1 absorption transition takes place in the blue spectral region leading to a yellow-orange body colour. As an example, Ce…”

Selective catalytic reduction of NO by NH3 over a Ce/TiO2 catalyst

“…The wide application of cerium oxide either as a promoter or as an active catalyst is due to its unique redox and acid-base properties. Labile oxygen vacancies and bulk oxygen species with relatively high mobility are easily formed during the redox shift between Ce 3+ and Ce 4+ under oxidizing and reducing conditions, respectively [15]. Long and Yang studied the performance of cerium oxide catalysts supported on Fe-ZSM-5 [16] and Fe-Ti-PILC [17] for the SCR of NO with NH 3 and concluded that cerium oxide enhanced the oxidation of NO to NO 2 , resulting in an improvement of activity.…”

Utilization of Nanoparticles Produced by Aqueous-Solution Methods – Formation of Acid Sites on CeO2-TiO2 Composite and 1-D TiO2 for Dye-Sensitized Solar Cells

“…To increase the temperature stability and ability of ceria to store and release oxygen, other transition and non transition metal ions (such as Al 3+ , Si 4+ , Ti 4+ and Zr 4+ ) are normally introduced into the ceria cubic structure (Reddy et al, 2003(Reddy et al, , 2005Rynkowski et al, 2000;Masui et al, 2002b). The redox and catalytic properties of CeO 2 are strongly influenced when it is combined with other transition metals.…”

“…A few studies on CeO 2 -TiO 2 composite nanoparticles (Reddy et al, 2003(Reddy et al, , 2005Rynkowski et al, 2000;Masui et al, 2002b) (Rynkowski et al, 2000), and stated the existence of the CeO 2 -TiO 2 composite. Masui et al also synthesized CeO 2 -TiO 2 composite nanoparticles, and reported the deactivation of the thermal and photocatalytic properties of this species by the formation of the CeO 2 -TiO 2 composite (Masui et al, 2002b).…”

“…Another is its structure: the stable structure of cerium oxide at room temperature under atmospheric pressure is the cubic fluorite structure in which oxygen ions do not have a close-packed structure. Owing to this structure, cerium oxide can easily form many oxygen vacancies while maintaining the basic crystal structure (Reddy et al, 2003). Cerium has a family of related mixed-valency binary oxides, which are anion-deficient and fluorite-related Ce 2 O 2n-2m between Ce 2 O 3 and CeO 2 at lower temperatures (Kang & Eyring, 1997).…”