Solid-state redox kinetics and reaction mechanism of Fe₂O₃/CeO₂–Al₂O₃ during methane reduction under chemical looping conditions

Chemical looping–based processes are attracting increasing attention as low-carbon energy conversion due to their inherent product separation. Their performance is mainly governed by the redox behavior and reaction kinetics of solid oxygen carriers, especially during the fuel reactor step involving methane reduction. Iron oxide is a promising oxygen carrier because of its low cost and environmental compatibility, but its limited reactivity at moderate temperatures motivates material modification. Among these strategies, cerium oxide has been introduced, although its effect on reaction kinetics is not yet fully understood. This study investigates the solid-state redox kinetics and mechanisms of CeO₂-modified Fe₂O₃/α-Al₂O₃ oxygen carriers. Temperature-programmed reduction revealed that Fe-CeαAl exhibited the lowest activation energies at 38.0, 70.6, and 93.3 kJ/mol, indicating up to 55% reduction in kinetic barriers due to Ce and α-Al₂O₃ synergy. During oxidation, temperature-programmed oxidation showed that Fe-CeγAl achieved the lowest activation energies at 40.4 and 54.5 kJ/mol, with a 50% decrease in oxidation barriers. Methane reduction in a fluidized bed showed a transition from diffusion to phase boundary control as porosity increased. CH₄-TPD confirmed enhanced gas–solid interaction. CeO₂ addition significantly improved redox performance, lowering the activation energy for methane reduction to 28.2 kJ/mol. These findings highlight Fe–CeαAl as a highly reactive and energy-efficient oxygen carrier. The results provide fundamental kinetic insight relevant to chemical looping systems and low-emission fuel conversion processes.