Carbon doping of ceria-supported palladium for the low-temperature oxidation of methane

Abstract

Cerium oxide-supported palladium nanoparticles (Pd/CeO₂) are poorly active toward the remediation of lean-burn exhausts at a “cold start” (operation temperature <300 °C) due to the presence of excessive palladium oxide (PdO) over the surface. Pd/CeO₂ was prepared by the wetness-impregnation method and subjected to a gas stream of methane (CH₄) and oxygen (O₂) at 230 °C. The supported Pd nanoparticles were partly converted to palladium carbide (PdC_x) due to carbon doping during this atmosphere treatment. This atmosphere-treated Pd/CeO₂ material exhibited improved catalytic performance towards remediation of a simulated lean-burn exhaust containing CH₄ and excessive O₂. Comprehensive characterization (scanning transmission electron microscopy, X-ray photoemission spectroscopy, thermogravimetry analysis/differential thermal analysis) of the material demonstrated that the improved catalytic performance of atmosphere-treated Pd/CeO₂ could be attributed to the oxidative decomposition of PdC_x species during catalysis, which created surface Pd sites to promote remediation of the lean-burn exhaust at <300 °C.