Catalytic decomposition of H2O2 on Co3O4 doped with Ag2O or ZnO

The effects of doping Co3O4 with Ag2O (0.40-3.00 mol%) or ZnO (0.75-6.00 mol%) on the surface and catalytic properties of the solid were investigated via nitrogen adsorption at -196 degreesC and the decomposition of H2O2 at 30-50 degreesC. Pure and doped samples were prepared by the thermal decomposition in air at 500-900 degreesC of pure cobalt carbonate and carbonate samples treated with different proportions of silver or zinc nitrates. The results, showed that Ag2O doping followed by precalcination at 500-900 degreesC resulted in a significant decrease (ca. 25%) in the BET surface areas of the treated Co3O4 samples. Treatment of Co3O4 with ZnO followed by precalcination over the same temperature range effected a corresponding increase in the specific surface areas (ca. 28%). The addition of Ag2O to Co3O4 effected a record increase in the corresponding catalytic activity towards the decomposition of H2O2. Thus, the maximum increase noted in the catalytic rate constant (k) measured at 30 degreesC over Co3O4 doped with 3.00 mol% Ag2O exhibited a 36-fold, 26-fold and 3.5-fold increase for catalysts precalcined at 500 degreesC, 700 degreesC and 900 degreesC, respectively. Treatment of Co3O4 with ZnO also effected an increase in the catalytic activity of the resulting solid. Thus, treatment of Co3O4 with 6.00 mol% ZnO followed by precalcination at 500 degreesC, 700 degreesC and 900 degreesC effected an increase of 109%, 28% and 36%, respectively, in the catalytic activity expressed in terms of the reaction rate constant measured at 30 degreesC. The doping process did not modify the activation energy of the catalyzed reaction but increased the concentration of catalytically active constituents considerably without changing their energetic nature. Doping with Ag2O or ZnO led to an increase in the concentration of Co3+-Co2+ ion pairs in the system and also generated corresponding Ag+-Co2+ and Zn2+-Co3+ ion pairs, thereby increasing the number of active constituents involved in the catalytic decomposition studied.