Hydrogen thermo-photo production using Ru/TiO2: Heat and light synergistic effects

Abstract

A series of ruthenium – anatase solids with noble metal loadings from 1 to 10 wt. %. was tested in the gas phase thermo-photo production of hydrogen using methanol as a sacrificial agent. Samples were characterized using X-Ray diffraction, UV–vis, X-ray photoelectron and absorption spectroscopies as well as transmission electron microscopy. A pure, high surface area anatase was present in all catalysts. It supports a ruthenium co-catalyst displaying a core-shell structure having an hcp metallic core and a RuO2-type shell structure. Activity, particularly under the combined use of light and heat, was analyzed by means of “excess” functions; the reaction rate and the quantum efficiency of the process were studied for thermo-photo vs. thermo/photo processes to provide conclusive evidence that the ruthenium-anatase materials display a strong synergistic use of both energy sources when utilized simultaneously. Optimum thermo-photo performance was achieved with a 5 wt. % Ru/TiO2 catalyst. An in-situ infrared study of the behavior of the gas-solid interface under the isolate or simultaneous action of heat and light was carried out to interpret the activity and analyze reaction mechanism. The study points out the key role of the ruthenium-anatase interface in activating carbon-containing species leading to carbon monoxide species subsequently transformed through a water gas shift type reaction. Activity seems directly correlated with the promotion of this step by light and heat within the context of a mechanism where methanol is previously oxidized in titania sites and such species evolves at the mentioned interface to generate hydrogen and carbon oxide molecules.