Interface-Induced Phase Evolution and Spatial Distribution of Fe-Based Catalysts for Fischer–Tropsch Synthesis

Fe-based catalysts undergo complex reduction, carburization, and phase interconversion as well as oxidation during Fischer–Tropsch synthesis (FTS). Unraveling the evolution of carbides and establishing the dominant factors are essential for rational design and modulation of Fe-based catalysts. In this work, Fe–oxide interfaces were constructed to investigate the effect on phase transformation and FTS performance. By correlating performance to the composition of iron species, the crucial role of Fe2.2C in high CO conversion and C5+ productivity has been confirmed. More importantly, a heterogeneous spatial distribution of iron carbides and oxides induced by Fe–oxide interfaces was observed. Fe3O4 preferentially forms at interfaces with the coexistence of carbon-rich Fe2.2C at subadjacent interfaces, while Fe5C2 locates at the region away from oxides or in the bare Fe catalyst. Further ex/in situ characterizations, including XPS, TPO, in situ XRD, and in situ IR, were conducted for revealing the mechanism. This study provides insights for iron carbides formation and stability by modulating interfaces, which guides the further development of Fe-based FTS catalysts.