Conditions and Mechanism for the Formation of CeFeO3 via Hydrogen Reduction of CeO2–Fe2O3 Mixed Oxides

Abstract

Cerium orthoferrite (CeFeO3) is a rare-earth perovskite oxide with potential catalytic and redox applications, but its bulk synthesis remains challenging because Ce3+ is readily oxidized to the stable Ce4+ oxide CeO2 under conventional preparation conditions. Herein, we demonstrate that CeFeO3 with high phase purity can be synthesized from CeO2–Fe2O3 mixed oxides by hydrogen reduction at 1073 K through control of the H2 partial pressure and gas flow rate. Powder X-ray diffraction and Rietveld refinement reveal that the phase purity of CeFeO3 strongly depends on the reducing conditions and increases with decreasing H2 partial pressure and flow rate. The highest phase purity, 99 mol % by Rietveld analysis, was obtained at PH2 = 1.25% and FH2 = 50.0 cm3 min–1. Analysis of H2 consumption, powder XRD patterns of intermediate products, and Fe K-edge and Ce L3-edge XANES spectra show that CeFeO3 forms through the reaction of CeO2 with FeO generated by the stepwise reduction of Fe2O3. These results establish hydrogen reduction of CeO2–Fe2O3 mixed oxides as a simple and controllable route to bulk CeFeO3 and clarify the competing reduction and phase-formation processes governing its synthesis.