Modulating Oxygen Transfer via A-Site Doping in LaFeO₃ for Coke-Resistant Chemical Looping Steam Methane Reforming

Chemical looping steam methane reforming (CL-SMR) is a promising technology for the simultaneous production of high-purity hydrogen and syngas without the need for external gas separation units. This study evaluates a series of A-site doped perovskite-type oxygen carriers, La_0.8A_0.2FeO₃ (A = Ca, Sr, Ba), to investigate the influence of alkaline earth metal doping on redox behavior and catalytic performance in CL-SMR. Substituting divalent cations at the A-site effectively promotes oxygen vacancy formation and enhances lattice oxygen transfer. Among the evaluated oxygen carriers, Sr-doped LaFeO₃ (La_0.8Sr_0.2FeO₃) exhibits the most favorable performance. This is attributed to the optimal concentration of oxygen vacancies, which improved oxygen transfer, as confirmed by X-ray photoelectron spectroscopy, cerimetric titration, and O₂-temperature programmed desorption. While undoped LaFeO₃ (LF) exhibits the highest methane activation, its limited oxygen mobility leads to severe coke formation. Enhanced oxygen transfer in La_0.8Sr_0.2FeO₃ effectively suppresses carbon deposition, while it shows the highest CO and hydrogen production. It achieves consistently high CO and H₂ yields (6.22-6.51 and 6.48-6.69 mmol/g_cat, respectively) and demonstrates excellent stability over 50 redox cycles.