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

Abstract

Five weight percentage of Pd/gamma-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 degreesC. 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. (C) 2004 Elsevier B.V. All rights reserved.