Partial oxidation and autothermal reforming of methane on Pd/CeO2–Al2O3 catalysts

Abstract

The surface properties and catalytic behavior of Pd/xCeO2–Al2O3 catalysts in partial oxidation of methane and autothermal reforming of methane were investigated. There was an increase on ceria's apparent crystallite sizes with the increase of CeO2 loadings and with the rise of the calcination temperatures of the supports from 500 to 900 °C. A decrease on the density of Pd sites was observed with the use of supports calcined at lower temperature and with the increase of CeO2 loadings. However, CO linearly bonded/CO bridged bonded intensity ratios showed an opposite trend. This apparent disagreement could be due to the partial coverage of Pd sites by CeOx species. Pd/Al2O3 catalyst was strongly deactivated during partial oxidation or autothermal reforming of methane, while catalysts with higher ceria loadings exhibited superior stability. Pd/xCeO2–Al2O3 catalysts show an increase of activity for autothermal reforming of methane with the increase of CeO2 loading. Therefore, the activity and stability apparently decrease with Pd dispersion. This fact was ascribed to partial coverage of Pd by [CePdxO]Pd0 species, which show high ability to promote the gasification of coke. The formation of [CePdxO]Pd0 species results in a decrease of the density of Pd sites but led to higher accessibility of the active sites to methane.