Lithium Promotes Acetylide Formation on MgO During Methane Coupling Under Non-Oxidative Conditions

A prototypical material for the oxidative coupling of methane (OCM) is Li/MgO, for which Li is known to be essential as a dopant to obtain high C-2 selectivities. Herein, Li/MgO is demonstrated to be an effective catalyst for non-oxidative coupling of methane (NOCM). Moreover, the presence of Li is shown to favor the formation of magnesium acetylide (MgC2), while pure MgO promotes coke formation as evidenced by solid-state C-13 NMR, thus indicating that Li promotes C-C bond formation. Metadynamic simulations of the carbon mobility in MgC2 and Li2C2 at the density functional theory (DFT) level show that carbon easily diffuses as a C-2 unit at 1000 & DEG;C. These insights suggest that the enhanced C-2 selectivity for Li-doped MgO is related to the formation of Li and Mg acetylides.

Automated summary

Li/MgO is a prototypical material for oxidative coupling of methane (OCM) with high C-2 selectivity. This study demonstrates that Li/MgO is also an effective catalyst for non-oxidative coupling of methane (NOCM). The presence of Li favors the formation of magnesium acetylide (MgC2), which promotes C-C bond formation and enhances C-2 selectivity.