Study on the structure and reduction behaviour of the iron–zirconium oxide system

Abstract

The structures and reduction behaviour of iron–zirconium oxides prepared by the coprecipitation method have been studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), BET surface-area measurements and Mössbauer spectroscopy. The structure of the iron-zirconium oxides is severely affected by the composition. For iron-zirconium oxides with different iron contents, the chemical states of the Fe³⁺ cations are quite different, and hence the reduction behaviour of these Fe³⁺ cations is quite different too. The various intermediates formed during the successive reduction steps of the iron–zirconium oxides were determined using TPR combined with in situ Mössbauer spectroscopy. For the samples with low iron content (⩽ 20 atom%), Fe³⁺ cations were doped in the lattice of cubic zirconia and were difficult to reduce to Fe°. By contrast, for the samples with high iron content (≫ 70 atom%), Zr⁴⁺ cations were doped in the lattice of α-Fe₂O₃ and the reduction of the Fe³⁺ cations to Fe° was easier than that of the samples with low iron content.