Oxidation of water by MnO4– mediated by thermally activated ruthenium dioxide hydrate

Abstract

The kinetics of oxidation of water to oxygen by MnO₄^–, mediated by thermally activated ruthenium dioxide hydrate, has been studied. The rate of catalysis is 0.8 order with respect to the surface concentration of MnO₄^–(which in turn appears to fit a Langmuir adsorption isotherm) and proportional to the catalyst concentration, but is independent of the concentration of manganese(II) ions. The catalysed reaction appears to have an activation energy of 50 ± 1 kJ mol^–1. These observed kinetics are readily rationalised using an electrochemical model in which the catalyst particles act as microelectrodes providing a medium for electron transfer between the highly irreversible oxidation of water to O₂ and the highly irreversible reduction of MnO₄^– to Mn²⁺.