Identification of active sites for CO and CH4 oxidation over PdO/Ce1−xPdxO2−δ catalysts

Abstract A PdO/Ce 1− x Pd x O 2− δ catalyst containing surface PdO x ( x  = 1–2) species and Ce 1− x Pd x O 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 CeO 2 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 CH 4 oxidation. For CO oxidation, the specific reaction rate of the surface PdO x species ( 673 .4 μ mol CO g Pd − 1  s − 1 ) was 249 times as high as that of the Ce 1− x Pd x O 2− δ solid solution ( 2 .7 μ mol CO g Pd − 1  s − 1 ), due to the fact that the surface PdO x species provided CO chemisorption sites. While for CH 4 oxidation, the specific reaction rate of the Ce 1− x Pd x O 2− δ solid solution ( 7 .5 μ mol CH 4 g Pd − 1  s − 1 ) was higher than that of the PdO/Ce 1− x Pd x O 2− δ catalyst ( 2 .8 μ mol CH 4 g Pd − 1  s − 1 ), due to the covered Ce 1− x Pd x O 2− δ surface by surface PdO x species.