N Restructuring of Iron-Based Catalysts Boosting the Formation of C₂₊ Olefins from CO₂ Hydrogenation

The electronic structure of the active centers of an iron-based catalyst can be modulated by neighboring N atoms in the hydrogenation of CO2. This work provides mechanistic insights into the relationship between the Fe4N active centers and carbon chain growth pathways. The Na/Fe4N catalyst exhibits higher selectivity toward CO and C2+ olefins with a higher olefin-to-paraffin (O/P) ratio and lower selectivity toward CH4. Through combined experimental evidence and theoretical calculations, we establish that the carbide-mediated pathway is more favored than the CO insertion mechanism on both the Fe4N and Fe5C2 catalysts. Furthermore, the energy barrier for C–C coupling on the Na/Fe4N(110) surface (0.62 eV) is lower than that on Na/Fe5C2(11–2) (0.98 eV). Comparative analysis reveals that Na/Fe4N has weaker hydrogenation capability compared to Na/Fe5C2 while possessing more CHx intermediates and nondissociatively adsorbed CO species. These fundamental insights into enhancing C–C coupling in iron-based catalytic systems are expected to offer guidance for the rational design of high-performance catalysts for CO2 utilization.