Probing Methane Coupling on Liquid Metal Indium: <i>In Situ</i> Elucidation of Active Sites

The nonoxidative coupling of methane (NOCM) offers a promising route to convert methane into value-added chemicals. Liquid metals have emerged as potential catalysts for NOCM, due to their propensity against coke formation and the flexible atomic arrangement that facilitates methane activation, with liquid state indium (In) gaining attention. However, the reaction pathways and catalytic mechanisms of In during NOCM have yet to be fully understood. Here, we report the discovery of locally generated In liquid metal active sites on In₂O₃ for the NOCM reaction, supported by silicon dioxide substrates, in the vicinity of an <i>in situ</i> formed In silicon oxide (In₂Si₂O₇) interfacial layer. By the implementation of combined <i>in situ</i> transmission electron microscopy and electron energy loss spectroscopy, we directly observed the formation of liquid metal "In active sites", near the interfacial layer, at >600 °C. The spectroscopy analysis reveals that In₂Si₂O₇ is a reservoir in methane conversion, storing reactive H* and CH _<i>x</i> * intermediate spillover from "In" for driving the NOCM reaction, avoiding the overcracking of CH₄ over metallic In. This finding provides a practical approach for the rational design of efficient and noncorrosive liquid metal-based catalysts.