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.