Preferential Oxidation of Carbon Monoxide in the Presence of Hydrogen (PROX) over Noble Metals and Transition Metal Oxides: Advantages and Drawbacks

The steam reforming reaction of hydrocarbons and organic fuels, in general, is followed by a two-stage reaction of water gas shift, which allows increasing the hydrogen yield and a final purification step for CO removal to use hydrogen in an ammonia plant or a PEM fuel cell. This paper is focused on the CO Preferential Oxidation, CO PROX (or CO selective oxidation in excess hydrogen) reaction, considered as the simplest and cost effective process to achieve the less than 10 ppm CO. The objective of this paper is to review the performances of noble metals (Pt, Ru, Rh, Pd), gold and transition metal oxides catalysts in this reaction. Although the results reported are largely influenced by the experimental conditions (reactant flow composition, mass of catalyst, duration of experiment …) a comparison of advantages and drawbacks for each type of catalysts is proposed in terms of activity and selectivity as well as of CO2 and H2O influences. A special attention will be paid to copper-doped ceria catalysts which appear to be very active and selective in a range of temperatures appropriate for fuel cell application. The performances, the stability and the low cost of these formulations compared to noble metal-based catalysts make them very attractive for an industrial application.