Effect of the Addition of CeO2 or MgO on the Oxygen Carrier Capacity and Rate of Redox Reactions of NiO/Fe2O3/Al2O3 Oxygen Carriers

Two compositions of mixed oxygen carriers (OCs), N1F1A1 (mole ratio of NiO to Fe2O3 is 1:1) and N1F2 (mole ratio of NiO to Fe2O3 is 1:2), were fabricated by mechanical mixing, and the effects of CeO2 and MgO additives on the oxygen-transfer capacity (OTC) and crystal structure were analyzed. In addition, X-ray diffractometry after the oxidation and the reduction steps was carried out to determine the reaction mechanism. Potential mixed OCs of the candidates of various OCs, such as NiO/Fe2O3, are proposed based on the OTC and oxygen-transfer rate evaluated via X-ray diffraction (XRD) phase analysis and thermogravimetric analysis. The chemical reaction equation for the oxidation and reduction was suggested based on the XRD characterization of the phases including NiFe2O4 and MgAl2O4 in N1F1A1 (①) and N1F1A1-Mg5 (④). Addition of MgO is confirmed to enhance the OTC and oxygen-transfer rate. The mechanism of the oxidation and reduction of metal oxides and the role of MgO were suggested. Even though the addition of MgO does not transfer oxygen to the fuel, it does accelerate the oxidation and reduction reactions of NiFe2O4.