Unlocked Covalent Competition in Asymmetric La/Sr‐O‐Fe Motif Activates Lattice Oxygen for Selective Methane Oxidation

Controlling lattice‐oxygen reactivity in transition‐metal (TM) oxides is essential for Mars‐van Krevelen selective oxidations, yet conventional strategies that tune TM 1 ‐O‐TM 2 bridges suffer from covalent competition between adjacent redox‐active cations, which generates site heterogeneity and degrades selectivity. Herein, taking Ruddlesden–Popper LaSrFeO 4 (A 2 BO 4 ) as a model, we demonstrate that constructing asymmetric A‐O‐B motifs (i.e., La‐O‐Fe and Sr‐O‐Fe) provides a distinct route to overcome this limitation. Combined experiments and DFT calculations reveal that the A‐O‐B configuration could convert redox‐inert A‐site cations into direct electronic contributors to oxygen, which unlocks the covalent competition, substantially enabling promoted electron density over oxygen and enhanced Fe─O bond covalency. Consequently, LaSrFeO 4 displays much lower methane activation barrier (∼1.24 eV) than its perovskite counterpart, LaFeO 3, with an Fe‐O‐Fe motif (1.90 eV), ultimately affording a 2.35‐fold increase in syngas yield with 97% selectivity. This discovery reveals that asymmetric A‐O‐B coordination may serve as a promising structural strategy, distinct from B‐O‐B modulation, for modulating the electronic properties and reactivity of lattice oxygen.