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

Abstract

The selective oxidative dehydrogenation of ethane with CO₂ (CO₂–ODHE) catalyzed by iron oxide (FeO_x) 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 FeO_x 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 FeO_x 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 FeO_x catalysts and offer a solid theoretical foundation for designing advanced catalysts for efficient, CO₂-integrated hydrocarbon conversion.