Oxygen transfer capacity of the copper component introduced into the defected-MgMnAlO4 spinel structure in CH4-CO2/air redox cycles

Oxygen carrier particles were fabricated by using defected-MgMnAlO4 as a support particle with crystal defects, and by the Cu2+ ions with a higher reduction potential substituted with Mg2+ ions, in order to use methane-chemical looping combustion (CH4-CLC) reaction. The oxygen transfer capacities of the particles were compared when conducting redox reactions under H-2/air or CH4-CO2/air systems. As a result, the oxygen transfer capacity increased as the amount of Cu ions added increased. In particular, in the CH4-CO2/air system, Cu0.75Mg0.25MnAlO4 particle showed an excellent oxygen transfer capacity of 7.62%. The XPS result confirms that the Cu2+ (also partially Mn3+ ions) in the Cu0.75Mg0.25MnAlO4 particle oxidize CH4, and then they are restored to their original state by receiving oxygen from the Al3+ and Mg2+ ions in the support. The oxygen vacancies in the lattice due to the Cu2+ could easily induce oxygen delivery, and the reversible oxygen loss recovery by re-oxidation in the air reactor could be achieved. This is the most important factor in increasing oxygen transfer capacity. Ultimately, in this study, oxygen defects in the crystal lattices induced during the reaction seem to have a positive effect on the CH4 combustion reaction.