In Situ Surface Chemistries and Catalytic Performances of Ceria Doped with Palladium, Platinum, and Rhodium in Methane Partial Oxidation for the Production of Syngas

Methane partial oxidation (MPO) chemically transforms natural gas into syngas for the production of gasoline. CeO2 doped with transition-metal ions is one type of catalyst active for MPO. A fundamental understanding of MPO on this type of catalyst is important for the development of catalysts with high activity and selectivity for this process. CeO2-based catalysts, including Pd-CeO2-air, Pd-CeO2-H-2, Pt-CeO2-air, Pt-CeO2-H-2, Rh-CeO2-air, and Rh-CeO2-H-2, were synthesized through doping noble-metal ions in the synthesis of CeO2 nanoparticles. The catalytic activity and selectivity in the production of H-2 and CO through MPO on these ceria-based catalysts as well as their surface chemistries during catalysis were investigated. They exhibit quite different catalytic performances in MPO under identical catalytic conditions. In situ studies of their surface chemistries during catalysis, using ambient-pressure X-ray photoelectron spectroscopy (AP-XPS), revealed quite different surface chemistries during catalysis. Correlations between the catalytic performances of these catalysts and their corresponding surface chemistries during catalysis were developed. Differing from the other four catalysts, Rh doped in the surface lattice of a CeO2 catalyst, including Rh-CeO2-air and Rh-CeO2-H-2, is in a complete ionic state during catalysis. Correlations between the in situ surface chemistry and the corresponding catalytic performance show that Rh ions and Pt ions doped in the lattice of CeO2 as well as metallic Pd nanoparticles supported on CeO2 are active components for MPO. Among these catalysts, Rh-doped CeO2 exhibited the highest catalytic activity and selectivity in MPO.