Chemisorbed acetate species derived from the adsorption of acetic acid have been oxidized on a nano-Au/TiO2 (∼3 nm diameter Au) catalyst at 400 K in the presence of O2(g). It was found that partial oxidation occurs to produce gold ketenylidene species, Au2=C=C=O. The reactive acetate intermediates are bound at the TiO2 perimeter sites of the supported Au/TiO2 catalyst. The ketenylidene species is identified by its measured characteristic stretching frequency ν(CO) = 2040 cm -1 and by 13C and 18O isotopic substitution comparing to calculated frequencies found from density functional theory. The involvement of dual catalytic Ti4+ and Au perimeter sites is postulated on the basis of the absence of reaction on a similar nano-Au/SiO 2 catalyst. This observation excludes low coordination number Au sites as being active alone in the reaction. Upon raising the temperature to 473 K, the production of CO2 and H2O is observed as both acetate and ketenylidene species are further oxidized by O2(g). The results show that partial oxidation of adsorbed acetate to adsorbed ketenylidyne can be cleanly carried out over Au/TiO2 catalysts by control of temperature.