Synthesis of iron-carbide nanoparticles: Identification of the active phase and mechanism of fe-based fischer-tropsch synthesis

Abstract

Despite the extensive study of the Fe-based Fischer-Tropsch synthesis (FTS) over the past 90 years, its active phases and reaction mechanisms are still unclear due to the coexistence of metals, oxides, and carbide phases presented under realistic FTS reaction conditions and the complex reaction network involving CO activation, C-C coupling, and methane formation. To address these issues, we successfully synthesized a range of pure-phase iron and iron-carbide nanoparticles (Fe, Fe5C2, Fe3 C, and Fe7C3) for the first time. By using them as the ideal model catalysts on high-pressure transient experiments, we identified unambiguously that all the iron carbides are catalytically active in the FTS reaction while Fe5C2 is the most active yet stable carbide phase, consistent with density functional theory (DFT) calculation results. The reaction mechanism and kinetics of Fe-based FTS were further explored on the basis of those model catalysts by means of transient high-pressure stepwise temperatureprogrammed surface reaction (STPSR) experiments and DFT calculations. Our work provides new insights into the active phase of iron carbides and corresponding FTS reaction mechanism, which is essential for better iron-based catalyst design for FTS reactions.