Oxygen-Promoted Methane Activation on Copper.

Area of Science:

• Surface Science
• Catalysis
• Materials Chemistry

Background:

• Methane conversion is crucial for energy and chemical industries.
• Understanding C-H bond activation on metal surfaces is key to developing efficient catalysts.
• The role of oxygen in modifying metal surface reactivity for methane activation remains an active research area.

Purpose of the Study:

• To investigate the influence of oxygen on methane C-H bond activation on Cu(111) and Cu2O(111) surfaces.
• To elucidate the reaction mechanism and identify factors governing activation barriers.
• To compare the reactivity of clean and oxygen-precovered copper surfaces.

Main Methods:

• In situ near-ambient-pressure scanning tunneling microscopy (AP-STM) for atomic-scale surface imaging.
• X-ray photoelectron spectroscopy (XPS) for surface chemical state analysis.
• Density functional theory (DFT) calculations to determine reaction pathways and energy barriers.

Main Results:

• Methane activation at 300 K and moderate pressures was observed exclusively on oxygen-precovered Cu(111) surfaces.
• DFT calculations revealed a two-active-site, four-centered mechanism for C-H activation on oxygen-covered Cu(111).
• This mechanism is stabilized by dipole-dipole interactions between O-H and Cu-CH3 species, lowering the activation energy barrier.
• Significantly higher C-H bond activation barriers were found on Cu2O(111) surfaces due to poor stabilization of reaction intermediates.

Conclusions:

• Chemisorbed oxygen on Cu(111) is essential for low-temperature methane C-H bond activation.
• The identified four-centered mechanism provides a detailed understanding of the catalytic process.
• Cu2O(111) surfaces exhibit limited activity for methane activation under the studied conditions, attributed to electronic and structural factors affecting intermediate stabilization.