Surface and catalytic properties of gamma-irradiated Cr2O3/Al2O3 solids

Two samples of Cr2O3/Al2O3 were prepared by mixing a known mass of finely powdered Al(OH)(3) with a calculated amount of CrO3 solid followed by drying at 120 degrees C and calcination at 400 degrees C. The amounts of chromium oxide employed were 5.66 and 20 mol\% Cr2O3, respectively. The calcined solid specimens were then treated with different doses of gamma-rays (20-160 Mrad). The surface and catalytic properties of the different irradiated solids were investigated using nitrogen adsorption at -196 degrees C and the catalysis of CO oxidation by O-2 at 300-400 degrees C. The results revealed that gamma-rays brought about a slight decrease in the BET surface area, S-BET (15\%), and in the total pore volume, V-p (20\%), Of the adsorbent containing 5.66 mol\% Cr2O3. The same treatment increased the total pore volume, V-p (36\%), and the mean pore radius, (r) over bar (43 \%), of the other adsorbent sample without changing its BET surface area. The catalytic activities of both catalyst samples were found to increase as a function of dose, reaching a maximum value at 80-160 Mrad and 40 Mrad for the solids containing 5.66 and 20 mol\% Cr2O3, respectively. The maximum increase in the catalytic activity measured at 300 degrees C was 59\% and 100\% for the first and second catalyst samples, respectively. The induced effect of gamma-irradiation on the catalytic activity was an increase in the concentration of catalytically active sites taking part in chemisorption and in the catalysis of CO oxidation by O-2 without changing their energetic nature. This was achieved by a progressive removal of surface hydroxy groups during the irradiation process.