An in situ IR technique was used to study the role of Au and Ag additives on photocatalytic reaction of ethanol on TiO2 at 300 K. Au and Ag additives increased water/ethanol coverage and decreased the rate of ethanol's C-H scission, a step involving in scavenging photogenerated holes. Au and Ag promoted adsorption of ethanol as monodentate ethoxy, accelerated its conversion to formate (HCOOad-) and acetate (CH(3)C00(ad)(-)). In contrast, adsorbed ethanol on TiO2 did not produce IR-observable products and exhibited a Stark effect with a decreased C-H intensity upon accumulation of photogenerated electrons. (C) 2015 Elsevier B.V. All rights reserved.