Acetic acid undergoes ketonization on iron oxide. The activation energy of the reaction depends on the region of temperature in which the reaction is carried out, indicating the dependence of the mechanism of the reaction on temperature. The nature of the primary activities of the catalyst effective in the ketonization, as well as the mechanistic model for ketonization, have been deduced from the study of the reaction in the presence of alcohols using the technique of competitive reactions. Below 400 °C, the ketonization reaction is a surface phenomenon involving the interaction of two adsorbed molecules of acetic acid, one of them forming ketene as an intermediate. At higher temperatures, the reaction takes place through the formation of a salt. © 1977.