Asymmetric coordination activated lattice oxygen in perovskite ferrites for selective anaerobic oxidation of methane

Abstract

Tuning lattice oxygen in iron-based oxides that efficiently activates methane while preventing an over-oxidation reaction remains challenging. This paper demonstrates the discovery of the construction of an asymmetric Fe–O–Al motif in perovskite ferrites to promote oxygen activity for the selective anaerobic oxidation of CH₄. Mechanistic studies reveal that Al doping renders accumulation of more electrons around the oxygen of Fe–O–Al (−1.20e) than around that of Fe–O–Fe (−1.08e), which improves Fe–O bond covalence, strengthens hydrogen adsorption (from CH₄) on oxygen, and reduces the activation barrier for C–H bond cleavage (0.87 eV for Fe–O–Al vs. 1.05 eV for Fe–O–Fe). The over-oxidation reaction is avoided due to an intimate Al–O interaction, leading to a higher oxygen vacancy formation energy of Fe–O–Al (3.81 eV) than that of Fe–O–Fe (3.43 eV). The synergy between Fe–O–Al for methane activation and Fe–O–Fe for oxygen supply enables enhanced methane-to-syngas performance, paving the way for designing prospective catalysts for chemical looping reactions or catalytic transformations concerning selective C–H bond activation.