Structural Characterization of Nanosized CeO₂−SiO₂, CeO₂−TiO₂, and CeO₂−ZrO₂ Catalysts by XRD, Raman, and HREM Techniques

Abstract

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.

Sol–Gel Synthesis of Tunable Cerium Titanate Materials

“…[6] Furthermore, numerous reports have studied the CeO 2 -TiO 2 mixed oxide from its catalytic properties. [7][8][9] Ce 2 Ti 2 O 7 pyrochlore is formed by Ce 3+ and Ti 4+ ions in eight and six-fold coordination respectively. The ionic radii of Ce 3+ and Ti…”

Recent Advances in Hydrogen Production Via Autothermal Reforming Process (ATR): A Review of Patents and Research Articles

“…Replacement of cerium ions by cations of different size and/or charge modifies ionic mobility inside the lattice resulting in the formation of a defective fluorite structured solid solution. Such modifications in the structure of CeO 2 confer new properties to the catalysts, such as better resistance to sintering and high catalytic activity [83,95,98].…”

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.…”

“…The redox and catalytic properties of CeO 2 are strongly influenced when it is combined with other transition metals. In addition, when the particle size is decreased below 100 nm, the materials become nanophasic, where the density of defects increases, such that up to half (50%) of the atoms are situated in the cores of the defects, promoting fast catalyst activation and reaction kinetics (Reddy et al, 2005). Thus, a study of the synthesis and reaction characteristics of nano-sized ceria-based mixed oxides is very important for utilizing the oxygen transport capacity and redox properties.…”