Ceria (CeO2) and Ir-doped CeO2 nanoparticles are tested for catalytic hydrogen-iodide decomposition in a thermochemical sulfur-iodine (SI) cycle. Ir-doped CeO2 strongly increases the hydrogen-iodide conversion as compared to pure CeO2 and also shows good stability for a time period of 5 h. The solution combustion method allows the incorporation of Ir metal ions into the CeO2 lattice and resulted in a different synergistic effect between Ir and Ce components such as increase in oxygen vacancies and oxygen mobility.