Redox reactions with colloidal metal oxides. Comparison of radiation-generated and chemically generated RuO2·2H2O

Abstract

Colloids of RuO₂· 2H₂O and MnO₂ have been produced by chemical and radiolytic methods. The colloids slowly aggregate upon standing in water over several weeks but radiolysis gives much smaller particles. The colloids are active in catalysing water oxidation under chemical and photochemical conditions although there is some corrosion. The chemically formed RuO₂· 2H₂O colloids are quite efficient catalysts for water reduction to H₂ but the radiolytically formed colloids do not promote H₂ formation. Colloidal MnO₂ is a poor catalyst for both H₂ and O₂ generation and it tends to aggregate under operating conditions. The RuO₂· 2H₂O colloids obtained by gamma radiolysis are selective for oxidation processes. They are stable and catalyse O₂ formation with high efficiencies. Such materials appear to be the best catalysts available for use in model systems for the photodissociation of water.