Probing The Structure Evolution of Iron-Based Fischer-Tropsch to Produce Olefins by Operando Raman Spectroscopy

By using operando Raman spectroscopy (ORS), we investigated the panoramic structure evolution of an iron oxide (alpha-Fe2O3) catalyst, which is used for the production of olefins via Fischer-Tropsch (FTO). During activation in different atmospheres and reaction at 260 degrees C and 3.0 MPa, alpha-Fe2O3 was only partially transformed into gamma-Fe2O3 by H-2 pretreatment; meanwhile, a transformation of alpha-Fe2O3 -> gamma-Fe2O3 -> Fe3O4 -> Fe5C2 was observed in both CO and syngas (H-2/CO). Combining with other techniques such as XRD, TEM, XPS and TPSR, we reveal that assembles of various iron oxides (gamma-Fe2O3, Fe3O4, Fe carbide, and their combinations) are responsible for FTO. Especially, the preliminary relationship of catalyst structure and performance relating to the production of olefins directly from syngas was established. Such a study is critical for further understanding of the FTO reaction and other catalytic reactions.