Highly Efficient Hydrogenation of CO2-Containing Syngas to Liquid Fuels over FeMnK Catalysts

Abstract

Converting CO2-containing syngas directly to liquid fuels provides an effective route for carbon-efficient fuel production. However, it is challenging to achieve the simultaneous conversion of CO and CO2 into liquid fuels due to the different activation pathways. Herein, a series of Mn- and K-promoted FeMnxKy catalysts were fabricated for the direct conversion of CO2-containing syngas into C5+ hydrocarbons. The optimal FeMn1K1 catalyst achieves 61.8% CO conversion with 73.2% C5+ hydrocarbon selectivity, including 50.9% C8−C16 hydrocarbon selectivity, corresponding to C5+ and C8−C16 hydrocarbon yields of 37.0% and 25.7%, respectively, under the reaction conditions of 320 °C, 2.0 MPa, 5100 mL gcat−1 h−1, and a H2/CO/CO2 ratio of 51/26/8, along with long-term stability for over 1000 h, demonstrating its promising industrial application. Spectroscopic characterizations of the spent FeMnK catalysts revealed that the high catalytic performance derives from a well-defined phase composition involving in situ formed ε-Fe2C, χ-Fe5C2, and Fe3O4 species. An optimal Mn content achieves a balanced phase composition among ε-Fe2C, χ-Fe5C2, and Fe3O4, whereas excessive Mn shifts the balance toward Fe3O4. K acts as an electronic promoter that enhances CO dissociation and suppresses olefin overhydrogenation, but excessive K promotes the oxidation of χ-Fe5C2 to Fe3O4. Mechanistic studies using H2/D2 isotope exchange, C3H6 and CO pulse hydrogenation, and operando diffuse reflectance infrared Fourier transform spectroscopy further elucidated the reaction pathway. The coexistence of ε-Fe2C, χ-Fe5C2, and Fe3O4 maximizes carbon utilization and provides a cost-effective, scalable route for liquid fuel production from CO2-containing syngas.