Fe₂O₃–MgAl₂O₄ for CO Production from CO₂: Mössbauer Spectroscopy and in Situ X‑ray Diffraction

Fe2O3/MgFeAlOx materials are promising oxygen storage candidates for chemical looping CO2 conversion. In this work, the cyclic stability of a 50Fe2O3/MgFeAlOx (containing 50 wt % Fe2O3 and 50 wt % MgAl2O4) oxygen storage material is investigated. The evolution of its bulk properties over the course of 1000 H2/CO2 redox cycles has been studied by means of 57Fe Mössbauer spectroscopy and in situ X-ray diffraction. As expected, all iron in the as-prepared oxygen storage material was present as Fe3+, 64% of which in iron-rich phases α-Fe2O3 and α-FeOOH and 36% in the form of a MgFeAlOx spinel. In contrast, after 1000 redox cycles, only 19% of iron was present in an iron-rich spinel such as Fe3O4, γ-Fe2O3, and MgFe2O4. The remaining 81% was present in the form of Mg–Fe–Al–O, including MgxFe1–xO. ILEEMS measurements showed surface enrichment of Fe3+ in 50Fe2O3/MgFeAlOx after 1000 redox cycles, with 36% of all surface Fe present as Fe3+ in iron-rich spinel phases such as γ-Fe2O3 and/or MgFe2O4