C-C Cleavage by Au/TiO₂ during Ethanol Oxidation: Understanding Bandgap Photoexcitation and Plasmonically Mediated Charge Transfer via Quantitative in Situ DRIFTS

Research into photoenhanced heterogeneous catalysis with Au/TiO₂ has gained traction in recent years because of the potential for activity enhancement due to its localized surface plasmon resonance effects, including oxidation reactions. While others have observed and described the effects of C-C cleavage by Au/TiO₂, how C-C cleavage occurs has not been reported to date. To elucidate the mechanism and to understand the fundamental impacts of visible and ultraviolet (UV) photoexcitation on the dynamics of gas phase ethanol oxidation, an in situ, quantitative diffuse reflectance infrared fourier transform spectroscopy analysis of the surface of Au/TiO₂ and neat TiO₂ was performed. Key findings from the study include (i) discovery of exclusive oxalate species, a critical precursor to C-C cleavage, which is also an indicator of selective ethanol adsorption at the Au-TiO₂ interfacial perimeter, (ii) fortification of C-C bond cleavage by Au/TiO₂ via detection of single-carbon species such as formate and carbon monoxide on Au/TiO₂ in the dark under visible light illumination, (iii) validation of previous postulations regarding ethanol adsorption on TiO₂ followed by oxygen activation at the Au-TiO₂ interfacial perimeter, and (iv) in situ re-enactment of the different impacts by bandgap photoexcitation and plasmonically mediated charge transfer, under UV and visible light illumination, respectively, on ethanol oxidation by Au/TiO₂ and neat TiO₂. (Chemical Equation Presented).