Pt and Au@TiO2 photocatalysts for methanol reforming: role of metal nanoparticles in tuning charge trapping properties and photoefficiency

Metal-loaded TiO2 is, by far, one of the most important class of photocatalysts in hydrogen production through photoreforming of organics and water photosplitting. In this study anatase loaded with Au and Pt nanoparticles (Au/TiO2 and Pt/TiO2) by an impregnation-reduction method was investigated as for morphological, electronic (XPS) and photocatalytic properties in hydrogen production by methanol photoreforming. The electron and hole trapping centers, Ti3+ and O-, respectively, formed under UV-vis irradiation of the photocatalysts, were studied by in situ electron spin resonance (ESR) spectroscopy. The nature of the loaded metal affected both the H-2 evolution rate and the distribution of the methanol oxidation products. The better performance of Pt/TiO2 is attributable to the greater ability of Pt with respect to Au to act as electron sink, slowering the recombination of photoproduced electron-hole couples. Direct evidence of this effect was obtained by ESR analysis, showing that the amount of Ti3+ active sites follows the order TiO2 >Au/TiO2 >> Pt/TiO2, thus confirming easier electron transfer from Ti3+ to Pt, where the H+ reduction to H-2 occurs.