C₂ Selectivity Enhancement in Chemical Looping Oxidative Coupling of Methane over a Mg–Mn Composite Oxygen Carrier by Li-Doping-Induced Oxygen Vacancies

Chemical looping oxidative coupling of methane (CLOCM) is a promising process for direct methane conversion to C2 products. Under the chemical looping approach, the oxygen carrier that provides lattice oxygen, in place of molecular oxygen, is used for methane oxidation. This study performs redox experiments that probe the C2 selectivity enhancement properties of a Mg–Mn composite oxygen carrier through the use of a low concentration of Li dopant. It was found that the C2 selectivity of the Li-doped oxygen carrier in CLOCM is universally higher than that of the undoped Mg6MnO8 oxygen carrier with a maximum improvement in selectivity of ∼50%. Density functional theory simulation reveals that the Li dopant has a short-range effect on the formation of oxygen vacancies. The Li-doping-induced oxygen vacancy reduces the adsorption energy of methyl radicals and increases the C–H activation barrier. These findings provide a catalytic dopant screening strategy for CLOCM, which will substantially enhance the C2 selectivity with desired oxygen carrier recyclability.