Localized partial oxidation of acetic acid at the dual perimeter sites of the Au/TiO₂ catalyst - Formation of gold ketenylidene

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.