Selective oxidation of CO in H2-rich stream over Au/CeO2 and Cu/CeO2 catalysts: an insight on the effect of preparation method and catalyst pretreatment

Selective oxidation of CO in H2-rich stream was studied on Au/CeO2 and Cu/CeO2 catalysts, investigating the effect of both the preparation technique and the catalyst pretreatment towards the catalytic performance. It was found that in the case of Au catalysts the sample prepared by deposition–precipitation was more active than that prepared by co-precipitation. The opposite trend was instead observed on Cu samples. On all tested catalysts a higher pre-calcination temperature of catalysts resulted in a lower CO conversion. The extent of this effect was strong on Au samples and less evident on Cu ones. On both Au and Cu samples selectivity towards CO oxidation decreased on increasing reaction temperature, being almost independent from preparation and pretreatment. On the basis of characterisation data (H2-TPR, XRD, XPS, and BET surface area) the effect of preparation method and catalyst pretreatment was accounted for both the different particle size and surface amount of active species (Au or CuOx). According to a Mars-van Krevelen mechanism, implying lattice oxygens of the cerium oxide and CO (and H2) adsorbed on the active species, it was suggested that on Au/CeO2 the PROX reaction is strongly affected by the status of gold, which has a key role in the CO activation step, whereas on Cu/CeO2 the performance are significantly influenced by the ceria morphology/reactivity.