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>Selective synthesis of the core–shell structured catalyst χ-Fe5C2 surrounded by nanosized Fe3O4 for the conversion of syngas to liquid fuels
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Selective synthesis of the core–shell structured catalyst χ-Fe5C2 surrounded by nanosized Fe3O4 for the conversion of syngas to liquid fuels
Enhancing liquid hydrocarbon selectivity and simultaneously suppressing CO2 formation are highly desirable yet challenging in iron-based Fischer–Tropsch synthesis. Herein, we report an in situ oxidation method for the fabrication of a functional configuration catalyst with a core–shell structure, namely, a χ-Fe5C2 core surrounded by a nanosized Fe3O4 shell, which promotes the formation of long-chain hydrocarbons on the inner χ-Fe5C2 as well as the depletion of primarily formed CO2 on the outer Fe3O4via the reverse water-gas shift reaction. The key to its success is the pretreatment of Fe3O4 under a syngas atmosphere with a H2/CO ratio of 2 at a high pressure of 20 bar and a high temperature of 400 °C. The pretreatment leads to an in situ formed high oxidation chemical potential atmosphere, which promotes the formation of the χ-Fe5C2@Fe3O4 core–shell structure. Moreover, the high-pressure pretreatment facilitates the formation of surface-graphitized carbon layers, leading to enhanced selectivity for long-chain hydrocarbons due to the electronic promotion effect of the graphitic structures. Such a functional configuration catalyst achieves a high C5+ hydrocarbon selectivity of 45% and a simultaneously low CO2 selectivity of only 7% with a CO conversion of 19% at 230 °C. These results offer a valuable reference for the rational fabrication of catalysts to suppress the usually high CO2 selectivity.
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