Co(II, III) Hydroxides Supported on Zeolite Acting as an Efficient and Robust Catalyst for Catalytic Water Oxidation with Ru(bpy)33+

Abstract

A novel highly efficient and stable for many cycles catalyst (1% Со-ZSM-5(17)) for water oxidation was developed using the method of polycondensation for stabilization of oxo/hydroxo complexes of cobalt (II, III) and nanosize Co3O4 in zeolite channels. In a weak-alkaline medium (pH 8.0, 9.2, 10.0) in the presence of a one-electron oxidant (Ru(bpy)33+), the catalyst provided the yield of oxygen as high as 56, 73 и 78% of the stoichiometric quantity, respectively. Catalysts based on ZSM-5 zeolite exhibited higher catalytic activity as compared to the catalysts based on the MOR, BEA, Y. Inspection of the electron states of cobalt in the Co-containing zeolite-based catalysts using TPR-H2 and UV–Vis DR techniques revealed that α-Co(OH)2-like polynuclear clusters and hydrocomplexes stabilized in the zeolite channels were most active to catalytic oxidation of water, while their transformation to Co3O4-like clusters/nanoparticles and Co2+ oxocomplexes, respectively, during thermal treatment led to some decrease in the catalyst efficiency. Coarsening of Co3O4-like clusters/nanoparticles caused the further decrease in the system efficiency. The minimal activity was observed with the catalysts containing predominantly isolated Co2 +Oh ions. The result obtained indicates a kind of at least polynuclear structure of the catalytically active center ConOx, where n > 2.