Selective oxidation of CO in H2-rich stream over gold/iron oxide: An insight on the effect of catalyst pretreatment

Selective oxidation of CO in H2-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 (H2-TPR, XRD, TEM) it was pointed out that, provided gold particles are small enough to be able to activate CO and H2, 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 H2 adsorbed on gold particles.

The performance of Au/iron oxide catalysts towards PROX reaction was found to be strongly affected by catalyst pretreatment. This was related to the change in the iron oxide phase caused by pretreatment. CO oxidation activity of iron oxide species was found in the order: ferrihydrite > hematite > magnetite. A Mars-van Krevelen mechanism, involving lattice oxygen of the iron oxide and CO and H2 adsorbed on gold, was proposed.Figure optionsDownload as PowerPoint slide