Surface and Catalytic Properties of γ-Irradiated Cr 2 O 3 /Al 2 O 3 Solids

Abstract

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°C and calcination at 400°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 γ-rays (20–160 Mrad). The surface and catalytic properties of the different irradiated solids were investigated using nitrogen adsorption at −196°C and the catalysis of CO oxidation by O₂ at 300–400°C.

The results revealed that γ-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, r̄ (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°C was 59% and 100% for the first and second catalyst samples, respectively. The induced effect of γ-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 O₂ without changing their energetic nature. This was achieved by a progressive removal of surface hydroxy groups during the irradiation process.