Examining the Cu–Mn–O Spinel System as an Oxygen Carrier in Chemical Looping Combustion

Chemical-looping combustion (CLC) and chemical-looping combustion with oxygen uncoupling (CLOU) are attractive alternatives to conventional combustion that provide efficient and direct separation of CO₂. Both processes use metal oxides as oxygen carriers to transfer oxygen between two reactor vessels: the air and fuel reactors. Although monometallic oxides (such as Mn₃O₄, Fe₂O₃, NiO, and CuO) have been successfully employed as oxygen carriers, double oxides of the general formula Cu_xMn_3−xO₄ in the CuO–Mn₂O₃ system are examined in this work. The carrier was produced by mixing, extruding, and calcining a 1:1 molar (30.8:69.2 mass ratio) mixture of CuO and Mn₂O₃ at 950 °C for 6 or 12 h in static air. XRD analysis revealed that spinels of the general formula Cu_xMn_3−xO₄ were formed with 0.1≤x≤2.5 in which x=3 Cu/(Cu+Mn). The chemical-looping performance was evaluated in a laboratory-scale fluidized-bed reactor from 800–850 °C over several alternating redox cycles using CH₄ as the fuel. The oxygen carrier exhibited reproducible and stable reactivity behavior for both reducing and oxidizing periods in this temperature range. This characteristic makes the system an ideal oxygen-carrier material for CLOU. Moreover, the spinels in the Cu_xMn_3−xO₄ series are endowed with favorable physicochemical attributes (such as fast redox processes, high crushing strength, and demonstrated CLOU behavior) and may be viable alternatives to CuO–Cu₂O and Mn₂O₃–Mn₃O₄ as potential CLOU materials.