Selective oxidation of CO in the presence of H2, H2O and CO2utilising Au/α-Fe2O3catalysts for use in fuel cells

Abstract

Au/Fe₂O₃ catalysts prepared using co-precipitation are described and discussed for the preferential oxidation of CO in the presence of H₂, H₂O and CO₂. A catalyst prepared using a two-stage calcination procedure (400 °C followed by 550 °C) achieves target conversion and selectivity (>99.5% CO conversion and >50% selectivity, based on O₂, for the competing conversion of H₂ with O₂ at 80–100 °C) for the competitive oxidation of dilute CO in the presence of moist excess H₂ and CO₂. The effect of the preparation method of the uncalcined precursor is described and the effects of calcination on the catalyst activity in the absence of H₂, CO₂ and H₂O is initially explored. The catalysts are characterised in detail using electron microscopy (TEM), X-ray photoelectron spectroscopy and Mössbauer spectroscopy. For the target conversion to be achieved, it is necessary that the activity for the reverse water gas shift activity (CO₂ + H₂ → CO + H₂O) of the catalyst is suppressed, since under the fuel cell conditions this reaction reforms CO at high CO conversions due to the presence of excess CO₂ and H₂. It is proposed that the two stage calcination procedure removes active sites for the water gas shift reaction whilst retaining active sites for preferential CO oxidation.