Operando DRIFTS was applied to the study of the evolution of surface species formed on a Pd (2 wt.%)/gamma-Al2O3 catalyst in various conditions. No differences were observed as a function of the initial oxidation state of palladium. Formates/carbonates species were identified at low temperature (< 400 degrees C) and disappeared when CO2 production started. These species come from the Pd-catalyzed interaction of CO with the alumina support, while CO2 induces hydrogenocarbonates formation at low temperature (< 300 degrees C). Their presence does not explain the inhibiting effect of CO2 observed in CCM on Pd/gamma-Al2O3 catalysts. (c) 2005 Elsevier B.V All rights reserved.