H-2/CO2 mixtures derived from biomass degradation may be regarded as a renewable source of hydrogen that could be used for hydrogenation reactions. The practicality of directly using a CO2-containing H-2 feed was evaluated during the hydrogenation of toluene to methylcyclohexane at 75 degrees C and ambient pressure. An operando DRIFTS study was carried out to unravel some of the mechanistic features of this reaction over a 0.88% Pt/Al2O3 catalyst, in particular to rationalize the loss of activity observed in the presence of CO2. We report, for the first time, a quantitative link between the loss of activity for hydrogenation and the formation of carbonyls adsorbed on the platinum, while the deactivation could not be correlated to the species formed onto the alumina, e.g. carbonates, hydrogenocarbonates and formates. (C) 2010 Elsevier Inc. All rights reserved.