Surface and Catalytic Properties of the Co 3 O 4 /MgO System Doped with Ag 2 O and MoO 3

Abstract

The effects on their surface and catalytic properties of doping 0.2Co₃O₄/MgO solids with Ag₂O or MoO₃ (0.2–1.0 wt%) were investigated using nitrogen adsorption at −196°C, the oxidation of CO by O₂ at 200–250°C and the decomposition of H₂O₂ at 30–50°C. The results revealed that doping the investigated system followed by calcination at 500–900°C brought about a progressive increase in the specific surface area to an extent proportional to the amount of dopants added. This led to an increase in the catalytic activities of the doped solids towards H₂O₂ decomposition, especially for solids calcined at 700°C and 900°C. However, this increase was more pronounced with MoO₃ doping. On the other hand, the catalytic activity of the investigated system in CO oxidation by O₂ expressed as the reaction rate constant per unit surface area (k̅) was found to decrease on increasing the amount of Ag₂O and MoO₃ added. Calcination of the investigated system at 900°C led to the effective dissolution of most of the cobalt oxide added into the MgO lattice to yield a CoO-MgO solid solution. Doping 0.2Co₃O₄/MgO solid followed by heating at 500, 700 and 900°C did not alter the mechanism of the catalytic reaction but increased the concentration of Co³⁺-Co²⁺ ion pairs acting as active sites in the process.