The ketonization of acetic acid has been studied on a chromia catalyst at 460 °C and at a contact time of 0.7 sec at various partial pressures in presence of tertiary butyl alcohol and benzyl alcohol. There is no inhibition of the ketonization of acetic acid in presence of tertiary butyl alcohol which undergoes only dehydration giving isobutylene and water. Benzyl alcohol, which undergoes only dehydrogenation to give benzaldehyde and hydrogen, suppresses the ketonization of acetic acid. Comparative studies of the reaction of isopropyl alcohol in mixture with acetic acid and also with propionic acid, under identical conditions, confirm the conclusion that the ketonization is caused by the same activity of the catalyst that is responsible for dehydration and dehydrogenation. It is suggested that the ketonization occurs through the interaction of two acetic acid molecules adsorbed on the surface of chromia, one of them utilizing the dehydrogenation activity for adsorption and the other utilizing the dehydration activity. © 1969.