The gas-induced stability of ceria-based water-gas shift (WGS) catalysts was studied. In highly reducing environments, the gold-ceria interaction could be lost, zerovalent gold was formed, ceria defects were annealed, and deactivation followed. The catalysts after use in various WGS gas mixtures were characterized by XPS to examine the oxidation state of gold, which changed with the reaction conditions. The WGS reaction was carried out at 300°C in the full gas mixture over 5.8AuCe(La)Ox for 2 hr. The CO conversion was over 65%. When the heater was turned off, during the cooling transient (2 hr), the same gas mixture except for H2O was kept flowing through the reactor. WGS reaction ceased. However, the CO oxidation reaction continued to occur to below 50°C, which accounts for the nearly full conversion of oxygen by the CO oxidation reaction. High CO conversion was recovered when the WGS reaction was restarted at 300°. Thus, shutdown-startup in the full WGS gas mixture with 0.5 mole % oxygen added does not affect the subsequent activity of the catalyst. Similar stabilization of the gold-ceria catalyst activity was observed in shutdown (to RT)-startup (at 150°C) cyclic operation of the WGS reaction with 0.5% O2 present in the full WGS reaction gas mixture. This is an abstract of a paper presented at the AIChE Annual Meeting and Fall Showcase (Cincinnati, OH 1/04/2005).