Revealing the activity of different iron carbides for Fischer-Tropsch synthesis

Exploring the structure of iron-based catalysts on the catalytic performance of Fischer-Tropsch synthesis (FTS) reaction has attracted much attention. With this in mind, the mixture of SiO2 or Al2O3 powder and non-porous iron oxide powder (α-Fe2O3) have been investigated for understanding the nature role of different iron carbides in the FTS reaction by adjusting the formation of iron carbides. Under the typical FTS reaction conditions, the CO conversion of Al2O3/α-Fe2O3 = 1 catalyst could reach up to 61.6 %, which is about 3.3 times that of the pure α-Fe2O3 catalyst. Based on the characterization results, including in situ XPS and CO-DRIFTS as well as Mössbauer spectra, it is found that the electronic state of iron atoms is affected by the existence of SiO2 or Al2O3, and the interactions of Fe-Si or Fe-Al are formed on the surface of iron powder, which plays an important role in formation of C-rich iron carbide active phase (ε-Fe2C). Although χ-Fe5C2 is usually as the active phase in the FTS reaction, we have found that the content of ε-Fe2C is more positive to activity.