Optimizing Oxygen\nVacancies through p‑Band\nCenter Modulation of Oxygen in the Li<sub>2</sub>WO<sub>4</sub>/Mg<sub>6</sub>MnO<sub>8</sub> Catalyst for Enhanced Oxidative Coupling of\nMethane: An Experi

Herein, we demonstrate a one-pot sol–gel-assisted\nprocedure\nto prepare a defect-rich Li<sub>2</sub>WO<sub>4</sub>/Mg<sub>6</sub>MnO<sub>8</sub> catalyst having surface oxygen vacancies, which facilitates\nthe adsorption of O<sub>2</sub> molecules to generate active oxygen\nspecies (O<sub>2</sub><sup>–</sup>, O<sub>2</sub><sup>2–</sup>) by incorporating Li and W into the Mg<sub>6</sub>MnO<sub>8</sub> lattice. These active oxygen species serve as primary active sites,\nselectively dissociating CH<sub>4</sub> into CH<sub>3</sub><sup>•</sup> and promoting CH<sub>3</sub><sup>•</sup> coupling into C<sub>2</sub>H<sub>6</sub>, while hindering excessive oxidation of CH<sub>3</sub><sup>•</sup> into CO<sub><i>x</i></sub>.\nVarious analytical methods such as XPS, O<sub>2</sub>-TPD, EPR, CH<sub>4</sub>-TPSR, in situ DRIFTS, and in situ Raman spectroscopy studies\ndemonstrated that surface reactive oxygen species are more active\nand selective than lattice oxygen toward the formation of C<sub>2</sub> products. The controlled addition of Li and W plays a crucial role\nin stabilizing surface Li species through the formation of Li–O–W\nbonds by forming the Li<sub>2</sub>WO<sub>4</sub> phase, ensuring\nstable catalyst performance up to 100 h. DOS analysis shows a positive\nshift in the p-band center, which effectively promotes the formation\nof oxygen vacancies. Analytical studies confirmed that surface active\noxygen species are more active and selective than lattice oxygen in\nforming C<sub>2</sub> hydrocarbons. The Li<sub>2</sub>WO<sub>4</sub>/Mg<sub>6</sub>MnO<sub>8</sub> catalyst exhibited superior performance,\nachieving ∼82% C<sub>2</sub> selectivity and ∼25% C<sub>2</sub> yield at 700 °C. We found that the stable formation\nof active oxygen species (O<sub>2</sub><sup>–</sup>) and a\nhigh Mn<sup>4+</sup>/Mn<sup>3+</sup> ratio over the surface are the\nkey factors for achieving high C<sub>2</sub> selectivity and yield\nduring OCM. DFT results show that the concentration of oxygen defect\nsites is higher on the surface of the Li<sub>2</sub>WO<sub>4</sub>/Mg<sub>6</sub>MnO<sub>8</sub> catalyst, which synergistically binds\nLi<sub>2</sub>WO<sub>4</sub> and Mg<sub>6</sub>MnO<sub>8</sub>, in\ncomparison with pure Mg<sub>6</sub>MnO<sub>8</sub> surfaces. Furthermore,\nDFT calculations also indicate that oxygen vacancies are energetically\nmore favorable on the surface of the Li<sub>2</sub>WO<sub>4</sub>/Mg<sub>6</sub>MnO<sub>8</sub> catalyst rather than in its subsurface. In\nsitu XRD and in situ Raman analysis demonstrated that Li<sub>2</sub>WO<sub>4</sub> undergoes a reversible phase change, transitioning\ninto a molten state at higher temperatures, potentially forming Li<sub>2</sub>O<sub>2</sub> species that may serve as active centers during\nthe reaction.