Codoping Mg-Mn Based Oxygen Carrier With Lithium And Tungsten For Enhanced C-2 Yield In A Chemical Looping Oxidative Coupling Of Methane System

Oxidative coupling of methane (OCM) is a compelling strategy for the direct conversion of methane to C2+ hydrocarbons in order to produce fuels and value-added chemicals. Nevertheless, it remains challenging to achieve the high C2+ yield that is desirable in industrial synthesis. Here, a lithium, tungsten-codoped Mg-Mn based oxygen carrier, (Li,W)-Mg6MnO8, is prepared for the chemical looping oxidative coupling of methane (CLOCM) technology. The designed codoped oxygen carrier exhibits an improved OCM performance with a C2+ yield of 28.6% at 850 degrees C, which is 80% higher than the combined yields of the single Li- and W-doped oxygen carriers, and 330% higher than that of the undoped Mg6MnO8 oxygen carrier. The enhanced activity has also been demonstrated over 50 redox cycles in the CLOCM system. In combination with solid characterization, density functional theory calculations reveal that, as compared to the single-metal-doped Mg6MnO8, the Li and W codopants work synergistically which not only enhances CH3 dimerization but also inhibits CO2 formation. This effect was attributed to the suppressed formation of unselective oxygen vacancies, which in turn leads to the C2+ yield enhancement. As a result, (Li,W)-Mg6MnO8 was found to be one of the best performing oxygen carriers as compared to other oxygen carriers reported in the literature. These findings provide new insights into the understanding of the codoping effect on the activity of a Mg-Mn based oxygen carrier for C2+ production and can open new avenues to design an environmentally and economically feasible CLOCM system.