Active Slingshot Geometry Site on Single-Atom La Catalyst Largely Promotes Oxidative Methane Coupling.

Oxidative methane coupling (OCM) has long been deemed a promising route for the direct conversion of methane to valuable ethylene. Despite its potential and many progresses, OCM's industrial implementation has been hampered by low C2 yields and insufficient understanding of the reaction mechanism for catalyst design. In this study, we present a surface geometric modification strategy to enhance OCM performance. Single La atoms incorporated onto MgO surface (SA-La/MgO) form a unique La-O-Mg "slingshot" geometry. This configuration, driven by the large atomic radius of La and its valency mismatch with Mg, significantly activates surface lattice oxygen. These activated oxygen species initiate the OCM by reacting with methane, while the resulting oxygen vacancies are rapidly replenished by dioxygen, sustaining active oxygen supply and preserving the structural integrity of single La atoms. These processes are realized by state-of-the-art in situ environmental electron microscopy and electron energy loss spectroscopy. Remarkably, the La-O-Mg "slingshot" geometry doubles C2 yields and significantly elevates the turnover frequency of SA-La/MgO compared to La2O3 particles on MgO, which lacks such active oxygen species. This work discovers a new mechanism for largely enhancing the OCM performance, emphasizing the importance of atomic-scale geometric and electronic modifications in catalyst design.