Effects of water on CO catalytic oxidation over Pd/CeO2

The role of water in CO oxidation was investigated on Pd/CeO2 with different morphologies (rods (R), cubes (C) and octahedrons (O)). Compared with the absence of water, CO oxidation activity increases 2 times in the presence of water on Pd/CeO2-C; but a decrease is found on Pd/CeO2-R. Catalyst characterization reveals that Pd is mainly in the form of solid solution (PdxCe1-xO2-sigma) on Pd/CeO2-R and a mixture of metal and PdxCe1-xO2-sigma solid solution on Pd/CeO2-C. The strong interaction between Pd and CeO2-R results in the form of stable bidentate carbonates species; while the relatively weak interaction between Pd and CeO2-C leads to the produce of unstable monodentate carbonates species. The effects of water on CO oxidation activity closely relate with the Pd chemical state and the types of carbonates species. Water restrains CO adsorption on PdxCe1-xO2-sigma solid solution, but it has negligent effects on metallic Pd species. In the presence of water, bidentate carbonates species remains stable but the decrease in the amount of monodentate carbonates species is observed. (C) 2020 Published by Elsevier B.V. on behalf of Chinese Society of Rare Earths.