Reliable oxygen transfer in MgAl2O4 spinel through the reversible formation of oxygen vacancies by Cu2+/Fe3+ anchoring

Abstract

This study focused on CuxMg1-xFeyAl2-yO4 oxygen carriers for application in the chemical looping combustion of methane. CuxMg1-xFeyAl2-yO4 was fabricated by simultaneously substituting Mg2+ and Al3+ with Cu2+ and Fe3+ in the spinel structure of MgAl2O4. As a result, a great synergistic effect was observed: Cu0.75Mg0.25Fe1.5Al0.5O4 exhibited 7.85% oxygen transfer capacity in the CH4-CO2/air redox system. Methane and carbon monoxide were significantly adsorbed on the surface of the CuxMg1-xFeyAl2-yO4 particles. Cyclic voltammetry studies predicted the active lifetime of the oxygen carrier, which had not been reported until now. Cu0.75Mg0.25Fe1.5Al0.5O4 was expected to exhibit the greatest oxygen transfer capacity after 300 redox cycles and maintain an oxygen transfer efficiency of 92% until the 1000th redox cycle in the H2-N2/air redox system. This study concluded that the active metal species, containing Cu2+ and Fe3+ ions, were stably anchored in the spinel structure; this led to the reversible formation of oxygen vacancies in the spinel structure, resulting in an excellent oxygen transfer capacity that could be maintained for a long time.