Development of MgMnO3-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 MgMnO3-δ with a defect cubic spinel structure as an oxygen carrier material with high efficiency, low cost, and stable properties. MgMnO3-δ has a non-stoichiometric oxygen content of MgMnO2.68. The reduced composition of MgMnO3-δ in H2, CO, or CH4 is a complete solid solution of (Mg,Mn)O. The redox reaction from MgMnO3-δ to (Mg,Mn)O is reversible and stable. Interestingly, MgMnO3-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 MgMnO3-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, MgMnO3-δ has a high tolerance to carbon deposition when used in CO or CH4 fuels.