Low-temperature deactivation and oxidation state of Pd/γ-Al2O3 catalysts for total oxidation of n-hexane

Five weight percentage of Pd/γ-Al2O3 catalysts were used for the oxidation of n-hexane. The activities of catalysts were greatly influenced by pre-treatments. The hydrogen-treated catalysts mainly with metallic palladium showed higher oxidation activities than the air-treated catalysts mostly with palladium oxide, even if the palladium oxide was known to be the active phase for high-temperature combustion of methane. The XPS and XRD analyses suggested that the oxidation state of palladium did not change during oxidation reaction at lower temperature of 180 °C. The reduced catalysts whose initial activities at lower temperatures were higher than the oxidized catalysts showed a gradual deactivation. This kind of low-temperature deactivation was attributed to the deposit of carbonaceous intermediates, which were evidenced through temperature-programmed analyses such as TGA and TPO.