Dispersion of Fe₂O₃ supported on metal oxides studied by Mössbauer spectroscopy and XRD

Abstract

The dispersion of Fe₂O₃ on various metal oxide supports (SiO₂, γ-Al₂O₃, CeO₂, ZrO₂ and TiO₂) has been studied by Mössbauer spectroscopy and XRD. The vacant sites on the surface of the support significantly influence the form of the iron oxide. For silica-supported iron oxide, Fe³⁺ cations concentrate readily to form crystalline α-Fe₂O₃ particles, owing to the lack of vacant surface sites on silica. However, for other metal oxide supports, such as γ-Al₂O₃, CeO₂, ZrO₂ and TiO₂, which have vacant surface sites, Fe³⁺ cations are preferentially incorporated into the vacant surface sites and the chemical surroundings of these Fe³⁺ cations, incorporated in different types of surface sites, are different. Crystalline α-Fe₂O₃ particles appear after all usable vacant sites have been occupied by Fe³⁺ cations.