Probing into the crystal plane effect on the reduction of α-Fe₂O₃ in CO by Operando Raman spectroscopy

For the Fe-based catalysts in Fischer-Tropsch synthesis, the reduction and activation process of α-Fe₂O₃ precursor has a significant effect on the catalytic performance. As a crystalline material, the reduction and activation of α-Fe₂O₃ is assuredly influenced by the exposed crystal plane; however, there is a lack of necessary research in this regard. In this work, α-Fe₂O₃ nanocrystals of three different morphologies, viz., pseudo-cubic, hexagonal-plate and rhombohedra, were synthesized, which mainly expose the crystal planes of (102), (001) and (104), respectively. The evolution of α-Fe₂O₃ crystal structure was then investigated in CO atmosphere by using the Operando Raman spectroscopy (ORS). The results show that the α-Fe₂O₃ (001) plane has a better reductive activity in comparison to the (104) and (102) planes. The SEM, TEM, XPS and XRD characterization and DFT calculation results reveal that CO₂ desorption is a decisive step for the reduction of α-Fe₂O₃; owing to the weak binding ability of (001) crystal plane to oxygen atoms, the desorption of CO₂ on the (001) crystal plane is much easier, which can promote the reduction process.