Enhanced Activity for CO Oxidation over Pr- and Cu-Doped CeO2Catalysts: Effect of Oxygen Vacancies

Ce 0.9Pr 0.1O 2-δ, Ce 0.95Cu 0.05O 2-δ, and Ce 0.9Pr 0.05Cu 0.05O 2-δmixed oxides and pure CeO 2were 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 0.95Cu 0.05O 2-δand pure CeO 2samples. Surface chemical states of the Ce 0.9Pr 0.1O 2-δand Ce 0.9Pr 0.05Cu 0.05O 2-δmixed 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 2and the Cu +ions provide chemisorption sites for CO.