A Kinetic Perspective on the Role of Fe ₅ C ₂ Facets for CO ₂ Hydrogenation to Olefins

Fe-based catalysts have demonstrated high efficiency for CO2 hydrogenation to olefins through sequential pathways involving the reverse water–gas shift (RWGS) reaction followed by Fischer–Tropsch synthesis (FTS). Fe5C2 has been identified as the active phase responsible for the latter FTS. However, the active sites for the initial RWGS reaction remain ambiguous. By modulating the prereduction conditions, Fe5C2 content is controllably regulated. It is found that Fe5C2 exhibits superior activity for RWGS compared to Fe3O4, based on integrated experimental evidence and theoretical kinetic analysis. The (021) and (510) facets of Fe5C2 are distinguished and display distinct CO2/H2 adsorption and desorption behaviors, which ultimately differentiate the product distribution. Specifically, the Fe5C2 (021) facet promotes moderate CO2/H2 adsorption and desorption, facilitating olefin production. The Fe5C2 (510) facet exhibits stronger CO2 adsorption with retarded H2 desorption, leading to possible alkane formation. In contrast, the relatively weak CO2 adsorption on Fe3O4 dominates methane formation and constrains its C–C coupling activity. Moreover, smaller particles exhibit superior performance, as they allow for easier penetration by CO2 and facilitate carbonization to form active Fe5C2. Overall, this study provides valuable insights into the rational design of effective catalysts for the hydrogenation of CO2 to olefins.