Understanding Plasmon and Band Gap Photoexcitation Effects on the Thermal-Catalytic Oxidation of Ethanol by TiO2-Supported Gold

To date there has been a lack of understanding on how photoexcited electron charge transfer can be beneficially combined in a hybrid photo-thermal-catalytic reaction. The effect of different excitation wavelengths on photo-thermal-catalytic oxidation by Au/TiO2 and TiO2 nanoparticles was studied via the gas-phase oxidation of ethanol over a temperature range of 100-250 °C under either visible light or UV illumination. Catalytic performance was assessed by monitoring the CO2 yield. Despite being a weak thermal catalyst (5% catalytic enhancement in comparison to neat TiO2 under thermal catalytic conditions), Au/TiO2 displayed a considerable photo-thermal synergism in the photo-thermal regime (>175 °C), with over 50% and 100% increases in catalytic performance in comparison to neat TiO2 under visible light and UV illumination, respectively. Photo-thermal-catalytic results and detailed probing of postreaction surface carbon species on Au/TiO2 indicated that photo enhancement under UV illumination was due to congruent roles of the photo and thermal catalysis, while photo enhancement under visible light illumination was due to plasmonic-mediated electron charge transfer from the Au deposits to the TiO2 support.