Role of transition metal in perovskites for enhancing selectivity of methane to syngas

This work investigates the role of transition metal at the B-site of ABO₃–type perovskite that affects the lattice oxygen transfer for the partial oxidation of methane. Two types, LaBO₃ and La_0.6Ca_0.4BO₃ (B = Fe, Mn, Co), were synthesized and investigated under repeated redox cycles. The Fe-based perovskite had a high tendency of partial oxidation, while the Co-based perovskite mainly led to the full oxidation of methane. The Co-based perovskite was enriched with the surface oxygen component due to the enhanced oxygen transfer from the lattice to the surface vacant site. On the other hand, the Fe-based perovskite showed a relatively low lattice oxygen transfer to the surface oxygen vacancy although it had the highest lattice oxygen ratio among the different B-site perovskites. The selectivity and the production amount of the syngas were improved when the amount of the surface oxygen was controlled by adjusting the re-oxidation extent of the carriers during the oxidation step. Through these experiments, La_0.6Ca_0.4FeO₃, which showed the highest syngas productivity with utilizing earth-abundant metals, was selected as an optimal oxygen carrier for methane reforming.