The effects of CO2 and H2O on the preferential CO oxidation in H-2-rich gases (PROX) over Au/alpha-Fe2O3 have been studied by kinetic and IR spectroscopic measurements at 80 degreesC. Addition of CO2 reduces the CO oxidation rate and the selectivity, which based on a blue shift of the linearly adsorbed CO in the IR spectra is attributed to coadsorption of CO2 on the gold particles or at the gold-metal oxide interface. Furthermore, deactivation is accelerated due to increased carbonate formation on the catalyst surface. Addition of H2O results in opposite effects. It increases the selectivity by suppressing the competing H-2 oxidation reaction. The CO oxidation rate is slightly accelerated. The deactivation is significantly diminished, which is ascribed to the transformation of surface carbonates into thermally less stable bicarbonate species. The extent of the effect of water addition depends strongly on the reaction temperature, being most pronounced at lower temperatures (40 degreesC). Under realistic conditions (25% CO2, 10-15% H2O, 80 degreesC) water reduces, but cannot completely compensate, the negative influence of CO2 on the PROX performance compared to CO2-free gas mixtures. (C) 2003 Elsevier Inc. All rights reserved.