Surface and catalytic properties of γ-irradiated Fe 2O 3Cr 2O 3/Al 2O 3 solids

Abstract

An iron, chromium, aluminium mixed oxides specimen having the nominal molar composition 0.125 Fe 2O 3 0.06 Cr 2O 3/Al 2O 3 was prepared and subjected to thermal treatment at 700°C. The calcined sample was exposed to different doses of γ-rays varying between 20 and 160 Mrad. The surface and catalytic properties of the different irradiated solids were studied using nitrogen adsorption at −196°C and catalysis of CO oxidation by O 2 at 225–300°C. The results showed that γ-irradiation at doses between 20 and 80 Mrad resulted in a progressive increase of specific surface area (10–36%), total pore volume (55–175%) and mean pore radius (41–105%) of treated adsorbents. Irradiation at doses above this limit led to a significant decrease in the magnitudes of different surface parameters which still measured higher values than those found for the un-irradiated sample. The catalytic activity increased monotonically as a function of the dose absorbed. The catalytic reaction rate constant, measured at 225, 250 and 300°C increased by 400, 170 and 115%, respectively by exposure to a dose of 160 Mrad. The increase in the reaction rate constant per unit surface area measured at the same reaction temperatures due γ-irradiation at 160 Mrad was 370, 155 and 102%. This treatment did not modify the mechanism of the catalytic reaction, but increased the number of catalytically active sites taking part in chemisorption and catalysis of CO oxidation reaction without changing their energetic nature.