The Relationship between the Structural Characteristics of α-Fe2O3 Catalysts and Their Lattice Oxygen Reactivity Regarding Hydrogen

https://doi.org/10.3390/ma16124466

In this paper, the relationship between the structural features of hematite samples calcined in the interval of 800–1100 °C and their reactivity regarding hydrogen studied in the temperature-programmed reaction (TPR-H₂) was studied. The oxygen reactivity of the samples decreases with the increasing calcination temperature. The study of calcined hematite samples used X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), and Raman spectroscopy, and their textural characteristics were studied also. According to XRD results, hematite samples calcined in the temperature range under study are monophase, represented by the α-Fe₂O₃ phase, in which crystal density increases with increasing calcination temperature. The Raman spectroscopy results also register only the α-Fe₂O₃ phase; the samples consist of large, well-crystallized particles with smaller particles on their surface, having a significantly lower degree of crystallinity, and their proportion decreases with increasing calcination temperature. XPS results show the α-Fe₂O₃ surface enriched with Fe²⁺ ions, whose proportion increases with increasing calcination temperature, which leads to an increase in the lattice oxygen binding energy and a decrease in the α-Fe₂O₃ reactivity regarding hydrogen.