Surface Structure-Dependent Mechanistic Modulation of the Selective Oxidative Dehydrogenation of Ethane with CO₂ over Iron Oxide Catalysts

The selective oxidative dehydrogenation of ethane with CO2 (CO2–ODHE) catalyzed by iron oxide (FeOx) provides a CO2-utilizing route for ethylene production, simultaneously utilizing greenhouse gases and enabling the efficient conversion of light alkanes. However, the diverse phases formed by FeOx catalysts under the reaction conditions expose surface structures with distinct Fe and O atom arrangements, complicating the identification of reactive active sites. In this study, we demonstrate the pivotal role of surface structures of FeOx catalysts in governing the ethylene formation activity and selectivity. Among various phases, Fe3O4 with octahedrally coordinated Fe terminations (Fe3O4–B2) is characterized by frustrated Lewis pair (FLP) and low oxygen vacancy formation energy, which synergistically promote ethane activation and facilitate the CO2-mediated regeneration of active sites via the Mars-van Krevelen mechanism. Additionally, the coordination geometry of surface Fe atoms optimizes the interaction between the Fe 4s orbitals and the π* orbitals of the ethyl group (C2H5), stabilizing C2H5 adsorption. This electronic stabilization is complemented by spatial confinement imposed by FLP, effectively suppressing C2H5 migration and inhibiting the formation of CH3CH intermediates in the dry reforming of ethane, thereby enhancing the ethylene selectivity. The synergistic role of electronic and geometric effects of the Fe3O4–B2 surface structure remarkably enhances ethylene selectivity while maintaining high catalytic activity. These findings provide mechanistic insights into the structure–activity–selectivity relationships of FeOx catalysts and offer a solid theoretical foundation for designing advanced catalysts for efficient, CO2-integrated hydrocarbon conversion.