Catalytic performances and the reaction mechanism of Co3O4/AC (AC=activated carbon) for aerobic oxidation of alcohols carried out in the liquid phase were investigated. Co3O4/AC shows a high activity for aerobic oxidation of benzyl alcohol, comparable to noble metal catalysts (e.g., Au/AC) even in the absence of additives or promoters (e.g., NaOH). Changing preparation conditions, such as treatment temperature and/or time, can affect the catalytic performances of Co3O4/AC, due to decomposition of surface groups of the carbon support. Careful studies show that low alcohol conversions are obtained with either Co3O4 or AC alone, which indicates that the high conversion observed over the Co3O4/AC is due to a synergistic effect between Co3O4 and AC. Parallel experiments using a high-surface-area covalent triazine framework or oxygen-inert carbon nitride as support for the Co3O4 catalyst also show lower conversions, which suggest that the ability of AC (in Co3O4/AC) to activate molecular oxygen is essential for the reaction. FTIR and XPS spectra taken from catalysts before and after the reaction confirm that oxygen activation proceeds mainly on the carbon support. As a result, it can be assumed that the alcohol dehydrogenation step proceeds on the metal oxide, whereas the oxygen activation step occurs mainly on the carbon support.