A Ce 0.9 Pr 0.1 O 2-δ solid solution was prepared by a sol-gel method. Changes in microstructure of the solid solution under different atmospheres (O 2 , He, and H 2 ) and temperatures were characterized by an in situ X-ray diffraction (XRD) technique. Raman peaks at 460 cm -1 ascribed to the F 2g vibration mode of CeO 2 in the fluorite structure and at 570 cm -1 ascribed to oxygen vacancies in the solid solution were studied by in situ Raman spectroscopy using 785-and 514-nm excitation laser lines, providing bulk and surface information, respectively. With a 785-nm laser line, the A 570 /A 460 ratio reflecting the oxygen vacancies concentration increased under O 2 and He while it first increased and then decreased under H 2 with increasing temperature. With a 514-nm excitation laser line, the A 570 /A 460 ratio decreased with increasing temperature under all atmospheres. The growth of the A 570 /A 460 ratio under the 785-nm laser line was due to the positive effects of high temperature and high concentration of oxygen vacancies and the negative effect of reduction of the sample under reducing atmospheres (He and H 2 ), while the decline in the A 570 /A 460 ratio under 514 nm was due to the dominant negative effect of the migration of surface Pr from surface to bulk during the heating process.

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Nanosized CuO-CeO 2 catalysts with high surface area (>90 m 2 g -1 ) were prepared by a modified citrate sol-gel method with incorporation of N 2 thermal treatment. CO temperature-programmed reduction results indicated that there are three CuO species in the catalyst, namely, the finely dispersed CuO, the bulk CuO, and the Cu 2+ in the CeO 2 lattice. Using CO oxidation as a model reaction, catalytic activity of each species was evaluated. It was found that the finely dispersed CuO species had the highest activity (183.3 mmol CO g Cu -1 h -1 ) and the bulk CuO had medium activity (100.4 mmol CO g Cu -1 h -1 ), while the Cu 2+ in the CeO 2 lattice had the lowest activity (21.3 mmol CO g Cu -1 h -1 ). Furthermore, the Cu 2+ species in the CeO 2 lattice could migrate to the catalyst surface to form finely dispersed CuO under high-temperature calcination or under reaction conditions, which could consequently enhance the catalytic activity.

Ce 0.9 Pr 0.1 O 2-δ , Ce 0.95 Cu 0.05 O 2-δ , and Ce 0.9 Pr 0.05 Cu 0.05 O 2-δ mixed oxides and pure CeO 2 were prepared with a sol-gel method and were characterized by XRD, in situ Raman, and in situ DRIFTS techniques. The XRD results confirmed the formation of Ce-Pr-O solid solution. The Raman results indicated that a higher concentration of oxygen vacancies was obtained on the Pr-doped samples compared to the Ce 0.95 Cu 0.05 O 2-δ and pure CeO 2 samples. Surface chemical states of the Ce 0.9 Pr 0.1 O 2-δ and Ce 0.9 Pr 0.05 Cu 0.05 O 2-δ mixed oxides were determined by in situ Raman spectroscopy, which indicated that the surfaces of the two mixed oxides were both close to oxidation state during the reaction, despite of the presence of reducing reactant CO in the gas mixture. The in situ DRIFTS results evidenced the chemisorption of CO in the Cu-containing samples. The catalysts were tested for CO oxidation, and it was found that the enhanced reactivity was closely related to the higher concentrations of the oxygen vacancies and the chemisorbed CO in the catalysts, due to the fact that the oxygen vacancies provide activation centers for O 2 and the Cu + ions provide chemisorption sites for CO.