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 Mg 6 MnO 8 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 C 2 selectivity with desired oxygen carrier recyclability.

Directly upgrading natural gas is limited by the stability of its primary component, methane, and process economics. Since the 1980s, oxidative coupling of methane (OCM) has shown potential to produce ethylene and ethane (C2s). The typical OCM approach catalytically converts methane to C2 products using molecular oxygen, reducing process efficiency. To overcome this, chemical looping OCM converts methane to hydrocarbons via intermediate oxygen carriers rather than gaseous cofed oxidants. The chemical looping approach for OCM has been studied mechanistically for the first time with a Mn–Mg-based catalytic oxygen carrier (COC). The COC delivered stable performance in a fixed bed for 100 cycles for more than 50 h with a 63.2% C2 selectivity and 23.2% yield. These experimental results and original process simulations of an OCM chemical looping system for C2 or liquid fuel production with electricity cogeneration present a direct method for methane utilization.

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Syngas is a valuable chemical intermediate for producing commodity chemicals, such as olefins, methanol, liquid fuels, etc. The chemical looping route for syngas production presents an attractive alternative to state-of-the-art technology, such as partial oxidation, autothermal reforming, and steam methane reforming. Out of the several chemical looping configurations, the co-current moving-bed reactor with iron titanium composite metal oxide particles has demonstrated a high-purity syngas production. In this study, an alternative reactor configuration (indirect chemical looping system) is proposed to the co-current moving-bed reactor system (direct chemical looping system) to enhance the syngas yield. The indirect chemical looping system consists of a fuel reactor and a syngas generation reactor, both operated in countercurrent mode, with respect to the gas–solid flow, as opposed to just one co-current fuel reactor in the direct chemical looping system. This unique gas–solid contact pattern in the indirect chemical looping system aids in greater utilization of CO2 and H2O and improves the thermodynamic performance for syngas production. Thermodynamic simulations in Aspen Plus software are performed for system analysis and comparison under isothermal and autothermal conditions. Isothermal analysis at several different temperatures and pressures, with and without co-injection of CO2/H2O, is conducted to explain the behavior of the proposed system. Autothermal operation of the system under different pressures is also evaluated to determine the maximum syngas yield within the constraints of a practical system for syngas production to further produce liquid fuels via Fischer–Tropsch synthesis. The results from these simulations are compared against the direct chemical looping system to highlight the difference in thermodynamic constraints between the two processes. The oxidation behavior of reduced Fe2O3–MgAl2O4 with CO2 and H2O is experimentally tested at different pressures and temperatures to gain an understanding for the syngas generation reactor in the indirect chemical looping 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 °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.