Identification of active sites for CO and CH4 oxidation over PdO/Ce_(1-x)Pd_xO_(2-δ) catalysts

摘要

A PdO/Ce_(1-x)Pd_xO_(2-δ) catalyst containing surface PdO_x (x=1-2) species and Ce_(1-x)Pd_xO_(2-δ) solid solution was prepared by a solution combustion method. It was found that the surface PdO_x species could be removed by nitric acid treatment. Also, partial Pd~(4+) cations in the CeO2 lattice migrated to the surface to form surface PdO_x species after high temperature calcination (500 °C). The catalyst was tested for catalytic CO and CH4 oxidation. For CO oxidation, the specific reaction rate of the surface PdO_x species (673.4 μmolco g_(Pd)~(-1) s~(-1)) was 249 times as high as that of the Ce_(1-x)Pd_xo_(2-δ) solid solution (2.7 μmol_(co) gp_(Pd)~(-1) s~(-1)), due to the fact that the surface PdO_x species provided CO chemisorption sites. While for CH4 oxidation, the specific reaction rate of the Ce_(1-x)Pd_xO_(2-δ) solid solution (7.5 μimol_(CH4) g_(Pd)~(-1) s~(-1)) was higher than that of the PdO/Ce_(1-x)Pd_xO_(2-δ)catalyst (2.8 μmol_(CH4) g_(Pd)~(-1) s~(-1)), due to the covered Ce_(1-x)Pd_xO_(2-δ) surface by surface PdO_x species.