Platinum supported on active carbon (Pt/C) is introduced as a novel kind of catalyst for the single-stage self-condensation and subsequent hydrogenation of acetone to methyl isobutyl ketone (MIBK) in the gas phase. The reaction was conducted in a continuously operated, backmixed Berty reactor at 1 MPa and 623 K. The nature of the acid-base sites catalyzing the aldol condensation was investigated by artificial alteration of the active carbon surface chemistry through oxidative pretreatments. Unexpectedly, the oxygen functional groups on the carbon surface were found to be of minor importance for the catalytic performance. Rather, there are strong indications that certain mineral components such as alkaline earth oxides and hydroxides embedded and finely dispersed within the carbon structure might be responsible for the activity in the aldol condensation. The main advantage of the Pt/C catalysts under investigation refers to their excellent stability in prolonged catalytic runs.