Ethanol photoreaction to Hydrogen over Au/TiO(2) catalysts: Effect of Au particle size and TiO(2) bulk structure

Abstract

Solar hydrogen production from renewables such as ethanol and water is potentially a key means of fuel generation either for direct combustion or to power fuel cells. To achieve this few methods are possible among them are those involving photocatalytic processes on semiconductor materials due to the simplicity of the concept and its technical feasibility. However, no materials have been found, to date, that can be used for this process. Among the most promising photo-catalysts are those composed of TiO2 based material in presence of a transition metal such as Au or Pd because of the simplicity of their structure and the present industrial knowledge. Gold catalysts with finite nanoparticle size have been found to be very active for specific reactions in dark conditions such as CO oxidation , . Yet, their potential as active materials for photoreactions has only received sporadic attention , , , and considerable work is needed because the size of Au, the size of the TiO2 particulate support and the nature of TiO2 can each, in turn, influence the photo-reaction rate. The rate of H2 production from water is so far very small to be used as a model system for materials study. Alcohol are known however to act as hole scavengers and when used in the appropriate environment (i.e., in presence of only traces of O2 as in the liquid phase) can be used in a systematic way to test for materials properties and help the design of the better photo-catalysts. We have opted for ethanol as an alternative feedstock to methanol for two main reasons. Firstly, ethanol is produced from renewable sources and secondly it is a realistic prototype for larger molecules as it has a carbon-carbon bond and thus serves as a prototype for larger organic compounds. In this work we are focusing on the effect of TiO2 polymorphs and size while keeping the Au particle size constant in order to extract information on the reaction rate. In addition we compare the effect of the polymorph of TiO2: Anatase and rutile separately and together