Low-Temperature Activation and Coupling of Methane on MgO Nanostructures Embedded in Cu₂O/Cu(111)

Abstract

The efficient conversion of methane into valuable hydrocarbons, such as ethane and ethylene, at relatively low temperatures without deactivation issues is crucial for advancing sustainable energy solutions. Herein, AP-XPS and STM studies show that MgO nanostructures (0.2−0.5 nm wide, 0.4−0.6 Å high) embedded in a Cu 2 O/Cu(111) substrate activate methane at room temperature, mainly dissociating it into CH x (x = 2 or 3) and H adatoms, with minimal conversion to C adatoms. These MgO nanostructures in contact with Cu 2 O/Cu(111) enable C−C coupling into ethane and ethylene at 500 K, a significantly lower temperature than that required for bulk MgO catalysts (>700 K), with negligible carbon deposition and no deactivation. DFT calculations corroborate these experimental findings. The CH 4,gas → *CH 3 + *H reaction is a downhill process on MgO/Cu 2 O/Cu(111) surfaces. The activation of methane is facilitated by electron transfer from copper to MgO and the existence of Mg and O atoms with a low coordination number in the oxide nanostructures. The formation of O−CH 3 and O−H bonds overcomes the energy necessary for the cleavage of a C−H bond in methane. DFT studies reveal that smaller Mg 2 O 2 model clusters provide stronger binding and lower activation barriers for C−H dissociation in CH 4 , while larger Mg 3 O 3 clusters promote C−C coupling due to weaker *CH 3 binding. All of these results emphasize the importance of size when optimizing the catalytic performance of MgO nanostructures in the selective conversion of methane.