Catalytic decomposition of H2O2 on Co3O4 doped with MgO and V2O5

The effects of doping of Co3O4 with MgO (0.46 mol%) and V2O5 (0.20-0.75 mol%) on its surface and catalytic properties were investigated using nitrogen adsorption at - 196 degrees C and decomposition of H2O2 at 30-50 degrees C. Pure and doped samples were prepared by thermal decomposition in air at 500-900 degrees C, of pure basic cobalt carbonate and basic carbonate treated with different proportions of magnesium nitrate and ammonium vanadate. The results revealed that, V2O5 doping followed by precalcination at 500-900 degrees C did not much modify the specific surface area of the treated Co3O4 solid. Treatment of Co3O4 with MgO at 500-900 degrees C resulted in a significant increase in the specific surface area of cobaltic oxide. The catalytic activity in H2O2 decomposition, of Co3O4 was found to suffer a considerable increase by treatment with MgO. The maximum increase in the catalytic reaction rate constant (k) measured at 40 degrees C on Co3O4 due to doping with 3 mol% MgO attained 218, 590 and 275% for the catalysts precalcined at 500, 700 and 900 degrees C, respectively. V2O5-doping of Co3O4 brought about a significant progressive decrease in its catalytic activity. The maximum decrease in the reaction rate constant measured at 40 degrees C over the 0.75 mol% V2O5-doped Co3O4 solid attained 68 and 93% for the catalyst samples precalcined at 500 and 900 degrees C, respectively. The doping process did not modify the activation energy of the catalyzed reaction but much modified the concentration of catalytically active constituents without changing their energetic nature. MgO-doping increased the concentration of CO3+-CO2+ ion pairs and created Mg2+-CO3+ ion pairs increasing thus the number of active constituents involved in the catalytic decomposition of H2O2 . V2O5-doping exerted an opposite effect via decreasing the number of CO3+-CO2+ ion pairs besides the possible formation of cobalt vanadate. (C) 2000 Elsevier Science B.V. All rights reserved.