Ketonisation of acetic acid to acetone was studied in the gas phase using gamma-Al2O3, TiO2, ZrO2 and CeO2 as the catalysts in the temperature range of 180-350 degrees C and ambient pressure. Catalyst activity was found to increase in the order Al2O3 < < TiO2 < ZrO2 < CeO2 . CO2-TPD showed that relatively weak base sites on oxide surfaces are essential for the ketonisation activity, whereas no relation between oxide acidity and catalytic activity was observed. Catalyst resistance to deactivation increased in the order CeO2 < < ZrO2 < TiO2 in parallel with the amount of coke formed. TiO2 (Degussa P25) and ZrO2 were found to exhibit the best performance as represented by their activity and stability to deactivation. CeO2 and ZrO(2)could be regenerated by air calcination to regain their activity. DRIFTS studies of acetic acid adsorption on oxide surfaces found facile exchange between adsorbed bidentate bridging acetate species and gas-phase acetic acid at 130 degrees C, well below temperature threshold of acid ketonisation, indicating fast equilibration of different forms of surface acetate species in the ketonisation system. At higher temperatures typical for acid ketonisation, in the absence of gas-phase acetic acid, the adsorbed bidentate bridging acetate-d(3) species were found to undergo H/D exchange with proton sites on oxide surfaces. This provides experimental evidence supporting the intermediacy of enolate species in acid ketonisation.