The Relationship between the Structural Characteristics of α-Fe[sub.2]O[sub.3] Catalysts and Their Lattice Oxygen Reactivity Regarding Hydrogen

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-H[sub.2]) 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-Fe[sub.2]O[sub.3] phase, in which crystal density increases with increasing calcination temperature. The Raman spectroscopy results also register only the α-Fe[sub.2]O[sub.3] 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-Fe[sub.2]O[sub.3] surface enriched with Fe[sup.2+] 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-Fe[sub.2]O[sub.3] reactivity regarding hydrogen.