Ceria supported group IB metal catalysts for the combustion of volatile organic compounds and the preferential oxidation of CO

Abstract

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 O2, which includes O2 consumed both for CO and H2 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°C) and Cu/CeO2 at higher temperature (maximum of 96.8% for CuCP at 150°C), whereas Ag catalysts always exhibited very low CO conversions (maximum of 16.7% for AgCP at 80°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, H2-TPR, surface area measurements, H2–D2 isotopic exchange, N2O and H2–O2 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.