Effect of Ag 2O doping on surface and catalytic properties of cobalt–magnesia catalysts

Abstract

Magnesia-supported Co 3O 4 catalyst, doped with 0.7–3.5 wt.% Ag 2O, was prepared by wet impregnation method then calcined in air at 500°C and 700°C. The produced phases were identified by XRD analysis. The surface properties of the pure and doped solids were studied by using N 2 adsorption at −196°C and their catalytic activities were determined by studying the oxidation of CO by O 2 at 150–300°C. The obtained results revealed that pure and doped mixed solids preheated in air at 500°C and 700°C consist of MgO and poorly crystalline Co 3O 4 phases. Doping with silver oxide resulted in a decrease in the specific surface areas for the treated solids calcined at 700°C and an increase in their values for doped solids fired at 500°C. However, this treatment brought about a significant modification in the catalytic activity of the doped solids. Doping with 0.7 wt.% Ag 2O at 500°C led to an increase of about 78% in the specific catalytic activity which was found to decrease on increasing the percentage of Ag 2O above this limit, falling to values smaller than that measured for the undoped catalyst. Doping at 700°C led to a progressive decrease in the activity of the treated solids to an extent proportional to the amount of dopant present. The doping process at 500°C and 700°C did not modify the mechanism of the catalytic reaction but altered the number of catalytically active sites contributing in the catalysis of CO oxidation by O 2 without changing their energetic nature.