The reformer sponge iron cycle produces hydrogen from hydrocarbons with high efficiencies and a high degree of purity. In this process, the gas purification step is performed by a cyclic redox reaction of the contact mass (iron oxide) with synthesis gas and steam at high temperatures. In order to get information about the lifetime of the contact mass, investigations of the cycle behaviour of the contact mass have been carried out. First experiments showed that iron oxide pellets without additives were deactivated quickly for the redox reaction due to sintering effects. SiO2, CaO and Al2O3 were added to the iron oxides, and the effects of different compositions were investigated. The contact mass was characterized before cycling, after 10, and 20 cycles by XRD, SEM, mercury porosimetry and Raman spectroscopy. It was shown that a higher content Of SiO2 prevents sintering of iron species during reduction and the subsequent oxidation with water vapour over 20 cycles at 800 degrees C. A quartz content below 6.5 wt% prevented the contact mass from reacting already after 5 cycles. (c) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.