Selective oxidation of CO in H-2-rich stream over gold/iron oxide: An insight on the effect of catalyst pretreatment

Selective oxidation of CO in H-2-rich stream was studied on iron oxide supported Au catalysts prepared by deposition-precipitation (AuDP) or coprecipitation (AuCP) and for comparison on commercial gold reference catalyst (AuRef), investigating in detail the effect of catalyst pretreatment towards the catalytic performance. On AuDP and AuCP samples CO conversion strongly decreased on increasing calcination temperature. On the AuRef sample the influence of calcination was, instead, less evident. On all tested catalysts a higher reduction temperature resulted in a lower CO conversion, the effect of reduction on catalysts activity exceeding that of calcination. On all samples selectivity towards CO oxidation decreased appreciably on increasing reaction temperature. The dependence of selectivity from pretreatment was negligible. On the basis of characterization data (H-2-TPR, XRD, TEM) it was pointed out that, provided gold particles are small enough to be able to activate CO and H-2, the catalytic behaviour of the Au/iron oxide system in the PROX reaction is strongly related to the support phase, being sensitive to the microcrystalline structure and the oxidation state of the iron oxide. CO oxidation activity of different iron oxide species was found in the order: ferrihydrite > hematite > magnetite. It was concluded that on Au/iron oxide the PROX reaction occurs through a Mars-van Krevelen type mechanism which involves lattice oxygen of the iron oxide and CO and H-2 adsorbed on gold particles. (C) 2008 Elsevier B.V. All rights reserved.