A pure Co₃O₄/Al₂O₃ sample was prepared by the wet impregnation method using finely powdered aluminium hydroxide and cobalt nitrate dissolved in the least amount of distilled water. Maintaining the amount of Co₃O₄ constant at 16.7 mol%, different samples were doped by impregnating with known amounts of cerium or vanadium nitrates prior to impregnation with cobalt nitrate. The pure and doped samples were precalcined at 600°C and 800°C, respectively. The dopant concentrations employed were 0.5, 1.0, 2.0 and 3.0 mol% CeO₂ or V₂O₅. The resulting materials were studied by XRD and EDX methods, N₂ adsorption at −196°C and CO oxidation by O₂ at 130–220°C.

The results obtained revealed that the surface concentrations of cobalt species in pure and variously doped Co₃O₄/Al₂O₃ solids precalcined at 600°C were more than twice those present in the bulk of these solids. Heating the doped solid at 600°C and 800°C increased the degree of dispersion of Co₃O₄ by decreasing the crystallite size. This effect was more pronounced in the case of V₂O₅ doping, with the surface concentration of cobalt species being increased to a greater extent than with CeO₂ doping. Similarly, heating the doped solid at 600°C resulted in a progressive but measurable increase in the lattice parameter of Co₃O₄ due to the formation of solid solutions.

On heating the V₂O₅-doped solid at 800°C, a portion of the added V₂O₅ inter-acted with Co₃O₄ to yield cobalt vanadate while the other portion contributed to the formation of a solid solution. Doping followed by heating at 600°C increased the catalytic activity of the doped solids in CO oxidation by O₂. In contrast, solids precalcined at 800°C exhibited the opposite effect. The doping process changed the concentration of active sites involved in the catalytic reaction rather than changing the mechanism of the catalytic reaction.