The ε-Fe₂C/Cu Interface Synergistically Boosts Highly Selective Fischer-Tropsch Synthesis toward Light Olefins

Traditional Fischer-Tropsch synthesis (FTS) on iron-based catalysts is limited by the Anderson-Schulz-Flory (ASF) distribution, with a maximum theoretical selectivity of 58% for the C₂-C₄ hydrocarbons, accompanied by substantial methane byproduct formation. Suppressing methane formation while enhancing light olefin selectivity is of great significance, however, it remains a major challenge in this field. Herein, we developed a series of Fe/Cu_x@Al₂O₃ surrounded catalysts, which in situ formed a unique ε-Fe₂C/Cu interfacial structure during the FTS. The optimized Fe/Cu_3.8@Al₂O₃ catalyst achieved 84.7% selectivity toward C₂-C₄ hydrocarbons, significantly exceeding the ASF distribution limit, with a low CH₄ selectivity of 8.9% and an unprecedented light olefin selectivity of 62.3%. Further investigation and theoretical calculations revealed that in the FTS reaction, CO and H₂ adsorbed and dissociated on the ε-Fe₂C surface, leading to the formation of CH_x and C_nH_m intermediates through hydrogenation and chain-growth processes. Meanwhile, H* dissociated on the Cu surface migrated to the adjacent ε-Fe₂C sites via hydrogen spillover. The appropriate supply of H* regulated the hydrogenation and desorption of CH_x and C_nH_m species, simultaneously suppressing CH₄ formation and limiting long-chain hydrocarbons (C₅₊) production. This work provides valuable insights and strategies for designing advanced FTS catalysts for the highly selective production of light olefins from syngas.