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 C-2 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 C-2 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 C-2 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 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 C-2 selectivity with desired oxygen carrier recyclability.