The PdO/Ce1–x Pd x O2−δ catalyst prepared by a solution-combustion method contained free surface PdO species and PdO species in Ce1–x Pd x O2−δ solid solution, whereas the PdO/CeO2 catalyst prepared by an impregnation method contained only free surface PdO species. The free surface PdO species could be removed by nitric acid. Contributions of the PdO species to catalytic CO oxidation were quantitatively evaluated. The free surface PdO species in the PdO/Ce1–x Pd x O2−δ catalyst had the highest activity (969.3 μmolCO gPd –1 s–1), those in the PdO/CeO2 catalyst had medium activity (109.0 μmolCO gPd –1 s–1), and the PdO species in the Ce1–x Pd x O2−δ solid solution had the lowest activity (13.2 μmolCO gPd –1 s–1). Synergetic effects of PdO species were responsible for the enhanced reactivity of the PdO/Ce1–x Pd x O2−δ catalyst, as the free surface PdO species provided CO chemisorption sites and the Ce1–x Pd x O2−δ solid solution generated more oxygen vacancies for oxygen activation.

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This study focuses on developing a catalyst for the removal of volatile organic compounds (VOCs) accompanied chlorinated volatile organic compounds (CVOCs). By a combination of depositionÀprecipitation and impregnation methods, a Pd/Cr 2 O 3 ÀZrO 2 catalyst was prepared and tested for catalytic oxidation of dichloromethane, ethyl acetate, and toluene. It was found that the Pd/Cr 2 O 3 ÀZrO 2 catalyst are very active for the catalytic oxidation of all these three different organics, due to the bifunctional catalysis of Pd and Cr. By comparing the catalytic performance of Cr 2 O 3 ÀZrO 2 , Pd/ZrO 2 , and Pd/Cr 2 O 3 ÀZrO 2 catalysts, it suggested that the Cr species are more active for dichloromethane and ethyl acetate oxidation, while the Pd species play a very important role in toluene oxidation.