Surface and catalytic properties of cobaltic oxide supported on an active magnesia

Abstract

The surface and catalytic properties of Co 3O 4 loaded on MgO were investigated using nitrogen adsorption measurements conducted at −196°C and oxidation of CO by O 2 at 150–300°C. The amounts of cobaltic oxide were 23, 37.5 and 47.5 wt.% Co 3O 4. The supported samples were prepared by impregnating a known amount of magnesium carbonate with cobalt nitrate dissolved in the least amount of distilled water followed by drying and calcination at 300–700°C. The results obtained revealed that the specific surface areas of various samples decreased monotonically as a function of both precalcination temperature and extent of loading. Moreover, the activation energy of sintering, Δ E s, was found to increase by increasing the amount of Co 3O 4 present. On the other hand, the catalytic activity of different samples were found to increase progressively by increasing the amount of Co 3O 4 present reaching a maximum value at 37.5 wt.% Co 3O 4 and decreased by increasing the extent of loading above this limit. The catalytic activity, expressed as reaction rate constant per unit surface area, was found to increase by increasing the precalcination temperature from 300°C to 400°C, then decreased progressively by increasing the temperature from 400°C to 700°C. This treatment did not modify the mechanism of the catalytic reaction but changed the number of catalytically-active sites taking place in chemisorption and catalysis CO-oxidation reaction by changing their energetic nature.