Effect of Al₂O₃ and MoO₃ Doping of Co₃O₄ Solid on its Surface and Catalytic Properties

Abstract

Pure and doped COP4 samples were prepared by thermal decomposition at 500-IOOO"C of pure basic cobalt carbonate and of the basic carbonate treated with aluminium nitrate and ammonium molybdate. The amounts of dopants added were varied within the range 0.75-6 mol% Alp, and 0.025-6 mol% MoO,. The influence of this treatment on the specific surface areas and catalytic activities of the COP4 solids was investigated using nitrogen adsorption at -196"C and studies of the decomposition of HPz at 3D-50"C.The results obtained revealed that doping of cobaltic oxide solids with either Alp) or MoO), followed by calcination at 500"C and 700"C, resulted in a progressive increase in the BET surface areas. This increase was, however, more pronounced in the case of MoO) doping. Calcination of the doped solids at 900"C led to an increase in the BET surface areas of the Alp,-treated solids and to a small decrease in the specific surface areas of the MoO,-doped samples.Calcination of the variously doped solids at 500-900"C brought about a decrease in their catalytic activity to an extent proportional to the amount of dopant added. Thus, treatment of COP4 solids with 6 mol% Alp, followed by calcination at 500"C, 700°C and 900°C effected a decrease of 36.9, 42.8 and 67.5% in their activities (expressed as reaction rate constant per unit area) measured at 300c. The decrease in the catalytic activity of COP4 solids due to MoO, doping was greater than that effected by Alp, doping. The doping process did not change the mechanism of the catalytic reaction but effectively decreased the concentration of CO)<--C0 2< ion pairs acting as the active sites involved in the catalytic process.