The present study is a follow-up of a previous one on a detailed kinetic modeling of the homogeneous decomposition of SO3-H2O vapor in the sulfur-iodine cycle for hydrogen production. In this paper, the activity and stability of complex metal oxides CexCu1-xO2-delta prepared by a sol gel method with x values ranging within 0.2-0.8 were studied for SO3-H2O vapor decomposition having a feed rate of space velocity of 5000 ml g(-1) h(-1) at 727 877 C. Sample Ce0.8Cu0.2O2-900 showed even higher activity than Pt catalyst at >800 degrees C and good stability at 850 degrees C for 60 h of continuous operation. The physicochemical properties and redox process of CuO/CeO2 catalysts for SO3 decomposition were characterized by temperature programmed reduction, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analyses. A redox mechanism was then proposed based on the characterization results and our previous homogeneous kinetic model. In this mechanism, both ceria-support and copper oxide clusters were reduced, oxidized, and interacted with each other. The overall effect was that CuO/CeO2 catalyst promoted the reaction of SO3 + O <-> SO2 + O-2, which was the limiting step of SO3 decomposition, by providing reactive oxygen. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.