Decomposition of H 2O 2 over manganese-chromium oxide catalyst in aqueous and alkaline solutions

Abstract

β-manganese dioxide with 0.1 chromic anhydride was thermally treated at different temperatures (250, 500, 750 and 1000 °C). The decomposition products were characterized by X-ray diffraction measurements. The catalytic activity of the thermal products for H 2O 2 decomposition was tested in aqueous and alkaline solutions. X-ray diffraction analysis revealed that the addition of 0.1 M CrO 3 stabilizes the β-MnO 2 crystalline form at 500 °C. The transformation of β-MnO 2 into cubic Mn 2O 3 was detected after heating at 750 °C. At 1000 °C a crystalline Mn 3O 4 was produced. The addition of 0.1 M CrO 3 to β-MnO 2 decreased the catalytic activity for H 2O 2 decomposition in aqueous solution. The addition of sodium hydroxide to the solution of H 2O 2 much enhanced the rate of decomposition. The activity of the mixed catalysts was found to be higher than that for pure β-MnO 2. This effect can be attributed to the intrinsic instability of H 2O 2 in alkaline medium and to the base catalysis by OH −.