A Pt/CeO(2) catalyst was prepared by sol-gel method. The as-received sample was successively oxidized, reduced and re-oxidized. The samples were characterized by X-ray diffraction (XRD), temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and hydrogen iodide (HI) catalytic decomposition activity evaluation for the sulfur-iodine cycle. The oxidative/reductive atmosphere affected the structure and performance of the catalyst by the strong metal-support interaction (SMSI). It was suggested that a migration of Ce(4+) from the bulk to the surface occurred during the reductive treatment. The diffusion process was reversed when the atmosphere was changed to an oxidative one. The decoration or encapsulation of Pt by ceria support changed with the atmosphere, and affected the activity of the catalyst. At temperature below 400 degrees C, the reduced sample exhibited the best activity. After then the activity of the reduced and re-oxidized samples tends to be the similar, but still better than the as received and oxidized samples. The surface and interfacial Pt(0) sites were both considered as the effective factors. Models were constructed to describe the diffusion of Ce(4+) and oxygen vacancies as well as the possible shell-core structure of Pt crystallites and the decoration/encapsulation by ceria support. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.