Synergetic Effects of PdO Species on CO Oxidation over PdO–CeO2 Catalysts

Abstract

The PdO/Ce1–xPdxO2−δ catalyst prepared by a solution-combustion method contained free surface PdO species and PdO species in Ce1–xPdxO2−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–xPdxO2−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–xPdxO2−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–xPdxO2−δ catalyst, as the free surface PdO species provided CO chemisorption sites and the Ce1–xPdxO2−δ solid solution generated more oxygen vacancies for oxygen activation.