Fuel cells and its fuel processor will be frequently shutdown and re-started depending on the power demand. Deactivation of Pt/CeO2 water-gas shift catalysts under conditions simulating shutdown was observed and studied using a combination of techniques such as Fourier transform infrared (Fr-IR) spectroscopy, high-resolution transmission electron microscopy (HRTEM), CO chemisorption and catalytic activity test. Results show that formation of carbonates occurs on the catalyst surface as a consequence of shutdown in reformate, leading to deactivation. The carbonates originating from both CO and CO2 cover not only the surface of CeO2 but also the Pt metal surface and exert an effect on its electronic properties. It is found that a correlation exists between the content of carbonates and the degree of deactivation. Regeneration by air treatment removes the carbonates and restores activity. Pt metal sintering is not found to be a factor contributing to the catalyst deactivation under the shutdown and re-startup conditions. (C) 2004 Elsevier B.V. All rights reserved.