Effect of γ-irradiation on some surface and catalytic properties of Cr2O3/Al2O3 solids precalcined at 700°C

The effects of gamma-irradiation (20-160 Mrad) on the surface characteristics (S-BET, V-p and (r) over bar) and catalytic properties (in CO oxidation by O-2) of chromia/ alumina solids have been investigated. The solids were prepared by mechanical mixing of CrO3 with finely powdered Al(OH)(3), followed by drying at 120 degrees C and calcination in air at 700 degrees C. The amounts of chromia in the samples were 8.2 wt% and 27.1 wt%, respectively. The results obtained show that doses of 20-40 Mrad brought about a measurable increase in the surface characteristics (S-BET, 46%; V-p, 93%; (r) over bar, 31%) of the sample containing 27.1 wt% Cr2O3 but doses above this limit had the opposite effect. However, the various surface parameters of the sample treated with 160 Mrad were still higher than those of the untreated sample. With the sample containing 8.2 wt% Cr2O3, varying the dosage of gamma-irradiation in the range 20-160 Mrad led to smaller variations in the surface parameters. The catalytic activities of both types of sample were decreased by gamma-irradiation, with the decrease being more pronounced for samples rich in chromia. Curves relating catalytic activity to dosage exhibited minima at 40 Mrad. The observed decrease in catalytic activity with gamma-irradiation was attributed to a decrease in the concentration of catalytically active sites taking part in chemisorption and catalysis of the oxidation of CO by O-2 without any change in their energetic nature.