Development of MgMnO_3-Δ as an oxygen carrier material for chemical looping combustion

Chemical looping combustion (CLC) is attracting attention as a promising technology for carbon dioxide separation. Oxygen carrier materials are the most important factor in determining the efficiency of CLC. In this paper, we present MgMnO_3-δ with a defect cubic spinel structure as an oxygen carrier material with high efficiency, low cost, and stable properties. MgMnO_3-δ has a non-stoichiometric oxygen content of MgMnO_2.68. The reduced composition of MgMnO_3-δ in H₂, CO, or CH₄ is a complete solid solution of (Mg,Mn)O. The redox reaction from MgMnO_3-δ to (Mg,Mn)O is reversible and stable. Interestingly, MgMnO_3-δ also shows a chemical looping oxygen uncoupling (CLOU) phenomenon and is reduced to MgMn₂O₄ and MgO in N₂ at 900 °C. The oxygen transfer capacities of MgMnO_3-δ under 15% H₂/N₂, 15% CO/CO₂, 15% CH₄/N₂, and 15% CH₄/CO₂ are 8.34, 8.56, 8.42, and 8.74 wt%, respectively, at 900 °C. The oxygen transfer capacity was well maintained during the 5th redox cycle. No phase or structure changes or agglomeration occurred as the redox cycle number increased. Moreover, MgMnO_3-δ has a high tolerance to carbon deposition when used in CO or CH₄ fuels.