The ketonization of monocarboxylic acids was studied in the presence of seven different Indian Ocean manganese nodules. The reactions were performed in a continuous flow reactor with varying temperatures, flow rates of reactant and amounts of catalyst. The activity of manganese nodules increases with the increase in MnO2, alkali and alkaline earth metal/oxides content. Complete conversion with high selectivity was achieved at 375 degrees C for acetic acid. A decrease in activity with increase in chain length of monocarboxylic acid was also observed.