An optimal Fe-C coordination ensemble for hydrocarbon chain growth: a full Fischer-Tropsch synthesis mechanism from machine learning

Qian-Yu Liu; Dongxiao Chen; Cheng Shang; Zhi-Pan Liu

doi:10.1039/d3sc02054a

An optimal Fe-C coordination ensemble for hydrocarbon chain growth: a full Fischer-Tropsch synthesis mechanism from machine learning

Chem Sci. 2023 Aug 11;14(35):9461-9475. doi: 10.1039/d3sc02054a. eCollection 2023 Sep 13.

Authors

Qian-Yu Liu¹, Dongxiao Chen¹, Cheng Shang¹, Zhi-Pan Liu^{1

2

3}

Affiliations

¹ Collaborative Innovation Center of Chemistry for Energy Material, Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials, Key Laboratory of Computational Physical Science, Department of Chemistry, Fudan University Shanghai 200433 China cshang@fudan.edu.cn zpliu@fudan.edu.cn.
² Key Laboratory of Synthetic and Self-Assembly Chemistry for Organic Functional Molecules, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China.
³ Shanghai Qi Zhi Institution Shanghai 200030 China.

Abstract

Fischer-Tropsch synthesis (FTS, CO + H₂ → long-chain hydrocarbons) because of its great significance in industry has attracted huge attention since its discovery. For Fe-based catalysts, after decades of efforts, even the product distribution remains poorly understood due to the lack of information on the active site and the chain growth mechanism. Herein powered by a newly developed machine-learning-based transition state (ML-TS) exploration method to treat properly reaction-induced surface reconstruction, we are able to resolve where and how long-chain hydrocarbons grow on complex in situ-formed Fe-carbide (FeC_x) surfaces from thousands of pathway candidates. Microkinetics simulations based on first-principles kinetics data further determine the rate-determining and the selectivity-controlling steps, and reveal the fine details of the product distribution in obeying and deviating from the Anderson-Schulz-Flory law. By showing that all FeC_x phases can grow coherently upon each other, we demonstrate that the FTS active site, namely the A-P5 site present on reconstructed Fe₃C(031), Fe₅C₂(510), Fe₅C₂(021), and Fe₇C₃(071) terrace surfaces, is not necessarily connected to any particular FeC_x phase, rationalizing long-standing structure-activity puzzles. The optimal Fe-C coordination ensemble of the A-P5 site exhibits both Fe-carbide (Fe₄C square) and metal Fe (Fe₃ trimer) features.