Catalytic carbon monoxide oxidation on X-irradiated alumina

Abstract

The catalytic oxidation of carbon monoxide in the presence of alumina has been studied in a flow system over the temperature range 25 ° to 400 °C. In the course of the reaction, the catalyst has been submitted to irradiation with X-rays (55 kV) at a dose rate of 2 × 10 19 eV g −1 h −1. Comparison of the results obtained under similar conditions with and without irradiation, indicates that, at a temperature below 300 °C, the catalytic activity of irradiated alumina is much higher. This fact may be related to the very important lowering of the activation energy under irradiation: 18 kcal for the unirradiated catalyst, about 0 kcal in the temperature range 80–300 °C and about 4 kcal at lower temperature for the irradiated one. Nevertheless the reaction order under irradiation remains the same as for unirradiated catalysts: it approaches unity with respect to CO pressure, and is comprised between one-fifth and one-half with respect to O 2 pressure. These results as well as previous ones related to the sorption of CO, O 2, and CO 2 on alumina submitted to irradiation lead to the conclusion that the rate-determining step for the catalytic oxidation of CO on Al 2O 3 is the chemisorption of O 2. This step is accelerated to a considerable extent by the irradiation of alumina.