Effect of gamma-irradiation on surface and catalytic properties of CuO-ZnO/Al2O3 system

A copper, zinc and aluminium mixed oxides sample having the nominal composition 0.25 CuO/0.03 ZnO/Al2O3 was prepared by impregnating Al(OH)(3) with copper and zinc nitrate solutions, drying at 100 degrees C then heating in air at 600 degrees C. The obtained solid was exposed to different doses of gamma-rays (20-160 Mrad). The surface characteristics namely SBETVP and r of different treated adsorbents were determined from N-2 adsorption isotherms measured at -196 degrees C. The catalytic activity of various irradiated solids was determined by following up the kinetics of CO-oxidation by O-2 at 150-200 degrees C. The results showed that the doses up to 80 Mrad resulted in no significant change in the S-BET but increased slightly the V-P (20%) of the treated adsorbents. The irradiation at 160 Mrad caused an increase of 20% in the S-BET of the irradiated solid sample. The catalytic activity increased progressively by increasing the dose, a dose of 160 Mrad brought about an increase of 140% in the catalyst's activity. The apparent activation energy of the catalytic reaction decreased monotonically by increasing the absorbed dose of gamma-rays which was attributed to a parallel induced decrease in the value of pre-exponential term of the Arrhenius equation. The observed increase in the catalytic activity due to gamma-irradiation has been interpreted as a result of increasing the concentration of catalytically-active sites contributing in chemisorption and catalysis of CO-oxidation via a possible fragmentation of CuO crystallites.