Surface and catalytic properties of gamma-irradiated CuO/Al 2O 3 solids

Abstract

Copper/aluminum mixed oxide solid, having the composition 0.25 CuO:Al 2O 3, was prepared by impregnating Al(OH) 3 with cupric nitrate using a pore-filling method, followed by heating in air at 300°C. The obtained solid was exposed to different doses of γ-irradiation, viz. 20, 40, 80, 120 and 160 Mrad. The surface area ( S BET), the total pore volume ( V p) and mean pore radius ( r ) of various treated solids were investigated by N 2 adsorption at 77 K. The catalytic oxidation of CO by O 2 on different irradiated catalysts was carried out at 95–145°C and a total pressure of 2 torr using a static technique. The results obtained revealed that γ-irradiation effected a decrease of 15–40% in the S BET and a decrease of 18–33% in the V' p of the treated solids. The doses up to 120 Mrad induced no important effect in the value of r which was found to increase (76%) by the exposure to a dose of 160 Mrad. In contrast, the irradiation process effected a considerable increase of 250–500% in the catalytic activity of the treated catalysts, depending on the dose employed and the temperature of the catalytic reaction. The activation energy of the catalytic reaction remained almost unchanged (9 ± 1 kcal/mol -1), indicating that the catalytic reaction took place via the same mechanism over different irradiated catalysts. These results were attributed to an increase in the concentration of the catalytically active sites, Cu 2+ cations, via desorption of strongly-bound chemisorbed oxygen and removal of OH groups from the outermost surface layers of the catalyst by absorption of γ-ray dose.