The water-gas shift (WGS) reaction over Au/Fe2O3 was studied by operando diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) combined with mass spectrometry (MS). Au/Fe2O3 and Fe2O3 were exposed to high temperature (400 degrees C) in He, followed by CO, H-2, or H2O treatment at 25 and/or 200 degrees C, respectively. The results showed that carbonate-like species and hydroxyl groups are present on the as-received sample, and not all of them are removed during high-temperature treatment at 400 degrees C. Although the dynamics of adsorbates on the catalyst surface have been observed at room temperature, at elevated temperature (200 degrees C)-that is, real operational steady-state conditions-the reduction-oxidation mechanism is the main pathway to the production of CO2 and H-2. Formates have not been observed under these reaction conditions. At elevated temperature, the support Fe2O3, in the presence of Au particles is easily reduced and contributes the catalyst performance for the WGS reaction. The water introduced to Fe2O3 does not contribute to reoxidation to a large extent and, consequently, to high CO2 production as observed over Au/Fe2O3. Furthermore, H-2 is evolved only in the presence of Au particles and when a certain degree of Fe oxide reduction is achieved. (c) 2006 Elsevier Inc. All rights reserved.