Catalytic promotion of NiO/MgO system by doping with some transition metal cations

Abstract

A nickel oxide–magnesium oxide sample having the formula 0.25 NiO/MgO was prepared by the homogeneous citrate method and subjected to heat treatment at 350 °C. This sample was impregnated with different proportions of cobalt, copper or manganese nitrate dissolved in the least amount of distilled water making pastes. The pastes were dried at 100 °C and then calcined at 500 °C. The extent of nickel was fixed at 20 mol% and those of dopant was varied between 0.5 and 7.4 mol% cobalt, copper and manganese ions, respectively. The analytical tools for characterization of different solids were atomic absorption, ion chromatograph IC, XRD, nitrogen adsorption at −196 °C and catalytic decomposition of H 2O 2 at 20–40 °C. The results revealed that the doping of the investigated system with copper and manganese species followed by calcination at 500 °C resulted in a decrease in the crystallite size of MgO phase while cobalt doping exerted an opposite effect. The doping process was, however, accompanied by an increase in the specific surface areas of the treated solids. Pure and doped samples precalcined at 500 °C consist of NiO/MgO solid solutions. The doping process brought about a considerable increase in the catalytic activity of the treated system. The increase was, however, much more pronounced in the case of manganese doping, which attained more than 350-fold for the reaction conducted at 20 °C. The doping process did not change the activation energy of the catalyzed reaction but much increase the concentration of active sites involved in H 2O 2 decomposition via creating new ion pairs.