Unveiling Cation‐Selective Evolution at Perovskite Step Edges for Boosted Anaerobic Methane Oxidation

Precisely tuning the catalytic behavior of perovskite oxides (ABO 3 ) remains challenging in catalysis, owing to the uncontrollable redistribution of metal cations at the surface. Herein, taking La 0.5 Sr 0.5 FeO 3‐δ as a model system, we demonstrate that high‐temperature annealing can induce a selective metal cation enrichment at surface step edges, transforming the dominant edge cations from Sr to Fe. This reconfiguration greatly enhances the intrinsic activity (normalized by specific surface area) by 57‐fold for selective anaerobic oxidation of methane. Mechanism studies reveal that Sr cations exhibit a higher segregation tendency than La and Fe below 900°C due to their relatively weaker bonding with lattice oxygen. Upon annealing at 1200°C, surface‐enriched Sr cations undergo segregation and volatilization, which would thereby expose adjacent Fe sites as highly undercoordinated and active centers for methane conversion. Our findings provide the direct experimental evidence for cation‐selective occupation at perovskite step edges, offering valuable guidance for the rational design of advanced perovskite‐based catalysts.