Catalytic combustion of volatile organic compounds (VOC) and preferential oxidation of CO (PROX) were investigated over IB metal/ceria catalysts prepared by deposition-precipitation (DP) or coprecipitation (CP). The activity towards the deep oxidation of VOC was in the order: Au/CeO2 >= Ag/CeO2 > Cu/CeO2 >> CeO2. The same trend was also found in the PROX reaction in terms of total conversion of O-2, which includes O-2 consumed both for CO and H-2 oxidation. A different behaviour was observed in the CO conversion to CO2. that is the desired PROX reaction. For this reaction, in fact, Au and Cu catalysts gave high CO conversions, Au/CeO2 at low temperature (maximum of 84.3% for AuDP at 70 degrees C) and Cu/CeO2 at higher temperature (maximum of 96.8% for CuCP at 150 degrees C), whereas Ag catalysts always exhibited very low CO conversions (maximum of 16.7% for AgCP at 80 degrees C). Both for PROX and VOC combustion the Au sample prepared by DP was more active than the CP one, whereas a reverse behaviour was found on Ag and Cu catalysts. On the basis of characterization data (XRD, H-2-TPR, surface area measurements. N-2-D-2 isotopic exchange, N2O and H-2-O-2 chemisorption) it was proposed that a higher atomic radius of the IB metal and the presence of smaller crystallites of both IB metal and ceria result in a larger enhancement of mobility/reactivity of surface ceria oxygens, involved in both investigated reactions through a Mars-van Krevelen mechanism. The very low PROX activity of Ag/CeO2 samples was related to the low capacity of silver to activate the CO molecule. (C) 2010 Elsevier B.V. All rights reserved.