Engineering Iron Carbide Phases by Modulating Layer Cations in LDHs for Low-CO ₂ Fischer–Tropsch to Olefins

Suppressing CO2 formation while preserving high selectivity toward light olefins remains a central challenge in the Fischer–Tropsch to olefins (FTO) process. Herein, we propose a strategy to regulate iron carbide phases by impregnating Fe species onto layered double hydroxides (LDHs) containing auxiliary elements (Ca or Mn) within their inorganic layers. These incorporated metal ions significantly influence the reduction and carburization behavior of iron species, thereby directing the evolution of distinct iron carbide phases. Specifically, CaAl-LDH leads to a mixed Fe5C2/Fe2C phase, whereas MnAl-LDH predominantly yields Fe5C2. Consequently, the Ca-promoted catalyst exhibits superior catalytic performance, achieving 79.1% CO conversion, 47.9% selectivity toward C2–C4 olefins, and a significantly suppressed CO2 selectivity of only 4.5%, clearly outperforming its Mn-based counterpart. In situ DRIFTS analysis reveals a cooperative catalytic mechanism involving Fe5C2 and Fe2C phases. This dual-site pathway directed carbon toward chain propagation rather than oxidation, thereby effectively suppressing CO2 formation. Our findings demonstrate that tuning iron carbide ensembles via engineering the support offers an effective route toward carbon-efficient FTO catalysis.