Surface and catalytic properties of gamma-irradiated CuO and NiO catalysts

Abstract

The effects of gamma-irradiation (20–160 Mrad) on surface and catalytic properties of CuO and NiO were investigated. The surface characteristics namely S BET, V p , and r ̄ of various solids were determined from nitrogen adsorption isotherms conducted at −196 °C and their catalytic activities were measured by following up the kinetics of CO-oxidation by O 2 using a static method. The results showed that gamma rays brought about a small increase (24%) in the S BET of CuO till a dose of 40 Mrad, and a dose of 80 Mrad was found to increase considerably its S BET (224%) due to narrowing of its pores ( r ̄ decreased from 110 to61Å). In the case of NiO solid its S BET was found to vary in a complex manner up on exposure to different doses of γ-rays. Gamma rays modified the catalytic activity of CuO catalyst in a complex manner. The catalytic activity of NiO, being expressed as the reaction rate constant k, was found to decrease progressively by increasing the dose in the range 20–120 Mrad. However, the reaction rate constant per unit surface area ( k ̄ ) of NiO decreased slightly (18%) by exposure to a dose of 20 Mrad. By increasing the dose to 40 Mrad a maximum specific catalytic activity ( k ̄ ) was observed. The further increase of the dose to 80 Mrad resulted in a sudden drop (69%) in the specific catalytic activity ( k ̄ ) of the treated solid. Irradiation at 120 Mrad brought about an increase (14%) in the value of k ̄ .