Surface and catalytic properties of the Co3O4/MgO system doped with Ag2O and MoO3

The effects on their surface and catalytic properties of doping 0.2Co(3)O(4)/MgO solids with Ag2O or MoO3 (0.2-1.0 wt\%) were investigated using nitrogen adsorption at -196degreesC, the oxidation of CO by O-2 at 200-250degreesC and the decomposition of H2O2 at 30-50degreesC. The results revealed that doping the investigated system followed by calcination at 500-900degreesC 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 700degreesC and 900degreesC. However, this increase was more pronounced with MoO3 doping. On the other hand, the catalytic activity of the investigated system in CO oxidation by O-2 expressed as the reaction rate constant per unit surface area ( (k) over bar) was found to decrease on increasing the amount of Ag2O and MoO3 added. Calcination of the investigated system at 900degreesC led to the effective dissolution of most of the cobalt oxide added into the MgO lattice to yield a CoO-MgO solid solution. Doping 0.2Co(3)O(4)/MgO solid followed by heating at 500, 700 and 900degreesC 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.