Chemical-Looping Steam Methane Reforming over a CeO2-Fe2O3 Oxygen Carrier: Evolution of Its Structure and Reducibility

Chemical-looping steam methane reforming (CL-SMR) is a promising method for the co-generation of pure hydrogen and syngas on the basis of redox cycles via a gas-solid reaction using an oxygen carrier. The performance and life of the oxygen carrier play pivotal roles in determining the feasibility and economy of the CL-SMR process. The present research was focused on the evolution of the structure and reducibility of a CeO2-Fe2O3 oxygen carrier during the CL-SMR redox process to further understand the sustainability of the oxygen carrier. The investigated CeO2-Fe2O3 complex oxide exhibited satisfactory performance in the CL-SMR process because of the chemical interaction between Ce and Fe species. A Ce-Fe-O phase equilibrium based on a stable composition of CeO2, Fe3O4, and CeFeO3 formed in the recycled samples. Surface oxygen was removed, which was accompanied by an increase in the concentration of oxygen vacancies and a decrease in the surface area of the recycled samples; these effects resulted in an increase in the high-temperature reducibility and syngas selectivity of the samples. Oxygen mobility was intensified by the Ce-Fe chemical interaction via the formation of CeFeO3 and a micromorphological transformation. These properties counteracted the sintering of the materials and guaranteed the stability of the oxygen carrier in the CL-SMR process.