Methane activation by diatomic molybdenum carbide cations

Area of Science:

• Catalysis
• Physical Chemistry
• Surface Science

Background:

• Metal carbides are emerging catalysts for methane activation.
• Understanding the fundamental mechanisms of methane transformation is crucial for developing new catalytic processes.

Purpose of the Study:

• To investigate the methane activation mechanism by the diatomic molybdenum carbide cation (MoC+).
• To elucidate the reaction pathways, including ethylene elimination and dehydrogenation.

Main Methods:

• Preparation and mass-selection of MoC+ ions using a quadrupole mass filter.
• Reaction of MoC+ with methane in a hexapole reaction cell.
• Detection of reactant and product ions via reflectron time-of-flight mass spectrometry.
• Density functional theory (DFT) calculations to explore reaction mechanisms.

Main Results:

• Observed products include bare Mo+ and MoC2H2+, indicating ethylene elimination and dehydrogenation.
• Ethylene elimination is the dominant reaction channel.
• DFT calculations revealed spin conversions (doublet→quartet and quartet→sextet) are crucial for ethylene elimination.
• The carbon atom in MoC+ becomes sp(3) hybridized, lowering energy barriers.

Conclusions:

• The diatomic cation MoC+ is an effective species for methane activation.
• Ethylene elimination is a favored pathway, driven by spin state changes and carbon hybridization.
• This research provides fundamental insights into C-H bond activation and C-C coupling in methane conversion over molybdenum carbide catalysts.