Chen Fanpeng,Cheng Chuanqi,Wang Jiajun,Han Yanran,Zhao Bo-Hang,Zhang Bin
Metastable carbides and chalcogenides are attractive candidates for wide and promising applications. However, their inherent instability leads to synthetic difficulty and poor durability. Thus, the development of facile strategies for the controllable synthesis and stabilization of metastable carbides is still a great challenge. Here, taking metastable ɛ -Fe 2 C as a case study, potassium ions (K + ) are theoretically predicted and experimentally reported to control the synthesis of metastable ɛ -Fe 2 C from an Fe 2 N precursor by increasing the surface carbon chemical potential ( μ C ). The controllable synthesis and improved stability are attributed to the better-matched denitriding and carburizing rates and the impeded spillover of carbon atoms in metastable ɛ -Fe 2 C with high carbon contents due to the enhanced surface μ C . In addition, this strategy is suitable for synthesizing metastable γ ’-MoC, MoN, 1 T -MoS 2 , 1 T -MoSe 2 , 1 T -MoSe 2 x Te 2(1− x ) , and 1 T -Mo 1 − x W x Se 2 , highlighting the universality of the methodology. Impressively, gram-level scalable metastable ɛ -Fe 2 C remains stable for more than 398 days in air. Furthermore, ɛ -Fe 2 C exhibits remarkable olefin selectivity and durability for more than 36 h of continuous testing. This work not only demonstrates a facile, easily scalable, and general strategy for accessing various metastable carbides and chalcogenides but also addresses the synthetic difficulty and poor durability challenge of metastable materials.
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/Cux@Al2O3 surrounded catalysts, which in situ formed a unique ε-Fe2C/Cu interfacial structure during the FTS. The optimized Fe/Cu3.8@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 CHx and CnHm 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 CHx and CnHm 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.
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