In this work, the activity values of Cu/Al2O3-, Fe/Al2O3- and Cu/Fe/Al2O3-composite granule catalysts prepared by a combination of Yolclas-process and oil-drop method were studied in an attempt to find some suitable catalysts for the decomposition of sulfur trioxide as the oxygen-generating reaction in the thermo-chemical water splitting process. The SO3 decomposition was performed in the temperature range of 750-950 degrees C at a space velocity of 72,000 mL/g cat. h in a fixed bed reactor. The catalytic activity of Cu/Fe/Al2O3-COMPOSite granule catalyst was better than that of Cu/Al2O3- and Fe/Al2O3-composite granule catalysts. The composite of Cu and Fe in the alumina granules increased the catalytic activity and found the optimum ratio of [Cu]/[Fe] = 1/2 with [Cu] + [Fe] = 0.125 M. (C) 2008 Elsevier B.V. All rights reserved.