Study on reduction and carburization behaviors of iron phases for iron-based Fischer–Tropsch synthesis catalyst

Reduction and carburization behaviors of iron phases over a precipitated iron-based Fischer–Tropsch synthesis (FTS) catalyst were investigated by some techniques of Mössbauer effect spectroscopy (MES), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) as well as H2&CO temperature-programmed desorption (H2&CO-TPD). It was found that in H2 atmosphere phase transformation of iron phases involved α-Fe2O3 → Fe3O4 → FeO → α-Fe, both occurring in the bulk and on the surface layers. All of reduced iron species took place the carburization reaction, whereas carburizing ability was following the order α-Fe > FeO > Fe3O4. During FTS both iron carbides and Fe(II) oxide species reached a balance state without appearing the intermediate α-Fe. The conversion of reduced iron phases to iron carbides (especially for χ-Fe5C2) on the surface layers played a positive role in promoting the formation of hydrocarbons species.