Synthesis and characterization of a ruthenium oxide-zeolite Y catalyst for photochemical oxidation of water to dioxygen

Abstract

In an integrated scheme for photochemical splitting of water to oxygen and hydrogen, there is a need for catalysts that couple the charge separated species to the redox reactions of water. Ruthenium oxide is well known as an efficient catalyst for photochemical four-electron oxidation of water to O₂. Zeolites are an excellent host for creating long-lived photochemically generated charge-separated species. There is a need for mild methods of incorporation of catalysts onto zeolites for water oxidation reactions. We report here that thermal decomposition of RU₃(CO)₁₂ on zeolite Y at 170°C produces Ru metal which is readily oxidized to RuO₂ by air. The morphology of RuO₂ on the zeolite is strongly dependent on the temperature at which air oxidation occurs. Samples of RuO₂-zeolite made by air oxidation at 200°C produce fibers of RuO₂ of approximate dimensions of length of 50 nm and widths of 5 nm. This material is found to be an efficient catalyst for oxidation of water to oxygen by photochemically generated Ru(bpy)³⁺₃ in solution. This study demonstrates that a specific morphology of RuO₂ is optimum for an effective catalyst, thereby suggesting that particular crystal faces of RuO₂ provide catalytic sites.