An observation of homogeneous and heterogeneous catalysis processes in the decomposition of H 2O 2 over MnO 2 and Mn(OH) 2

Abstract

The kinetics of peroxide decomposition by manganese dioxide (MnO 2) and manganese hydroxide (Mn(OH) 2) have been studied in alkaline solutions. The activity for peroxide decomposition on Mn(OH) 2 was generally higher than MnO 2 and the kinetics for the decomposition of H 2O 2 were first-order in the case of MnO 2 catalysts, but 1.3-order for Mn(OH) 2 catalysts. It is suggested that H 2O 2 is mainly homogeneously decomposed by Mn 2+ ions (in the form of HMnO 2 ions in concentrated alkaline solutions) dissolved in the solution in the case of Mn(OH) 2. Compared with the results reported for the decomposition of H 2O 2 in the presence of 1 ppm Co − 2 ions, it is concluded that the kinetics of the homogeneous decomposition of H 2O 2 are directly influenced by the concentration of the active species in the solution.