Effects of gamma-irradiation on physicochemical state of surface and catalytic properties of CuO/MgO and NiO/MgO systems

Copper and nickel oxide samples supported on MgO were prepared by wet impregnation method. The obtained solids were heated at 350degreesC and 450 degreesC. The extent of copper and nickel oxides was fixed at 16.7 mol%. The effect of gamma-irradiation (0.2-1.6 MGy) on the surface and catalytic properties of the solids were investigated. The techniques employed were XRD, nitrogen adsorption at -196 degreesC and H2O2 decomposition. The results revealed that the gamma-irradiation up to 0.8 MGy of CuO/MgO-450 degreesC effected a measurable decrease in the crystallite size of CuO phase with subsequent increase in its degree of ordering. Irradiation at a dose of 1.6 MGy brought about a complete conversion of MgO into Mg(OH)(2) during its cooling from 450 degreesC to room temperature via interacting with atmospheric water vapor. The S-BET and total pore volume of CuO/MgO precalcined at 350 degreesC and 450 degreesC increased progressively as a function Of gamma-ray dose reached a maximum limit at 0.8 MGy. Gamma-irradiation of NiO/MgO-450 degreesC solids up to 0.8 MGy increased the degree of ordering of MgO and NiO phases without changing their crystallite size. The exposure of these solids to 1.6 MGy led to an effective transformation of some of NiO (not dissolved in MgO lattice) into Ni(OH)(2) via interacting with atmospheric water vapor during cooling from 450 degreesC to room temperature. Gamma-irradiation led to a measurable increase in the S-BET and V-p of NiO/MgO system. Gamma-irradiation of the two investigated systems resulted in both increase and decrease in their catalytic activities in H2O2 decomposition depending mainly on the irradiation dose and calcination temperature. This treatment, however, did not modify the mechanism of the catalytic reaction, but changed the catalytic active sites without changing their energetic nature.