Coupling reactions in aldehydes adsorbed on V(100) single-crystal surfaces

Area of Science:

• Surface science
• Heterogeneous catalysis
• Chemical kinetics

Background:

• Formaldehyde is a key C1 building block in chemistry.
• Understanding formaldehyde surface reactions is crucial for catalysis.
• Vanadium surfaces are relevant in various catalytic processes.

Purpose of the Study:

• To elucidate the reaction mechanism of formaldehyde on vanadium (100) surfaces.
• To identify the pathways leading to ethylene formation.
• To investigate the role of intermediates in formaldehyde thermal chemistry.

Main Methods:

• Temperature Programmed Desorption (TPD)
• X-ray Photoelectron Spectroscopy (XPS)
• Isotope-labeling experiments under ultrahigh vacuum (UHV) conditions

Main Results:

• Ethylene desorption observed at two distinct temperatures: 290 K and 540 K.
• Low-temperature ethylene formation proceeds via methylene coupling after C-O bond dissociation.
• High-temperature ethylene formation requires a diolate intermediate (-OCH(2)CH(2)O-).
• The observed chemistry is general and applicable to coadsorbed aldehydes.

Conclusions:

• Two distinct mechanisms govern ethylene formation from formaldehyde on vanadium.
• Surface intermediate structures (methylene, diolate) dictate reaction pathways and product distribution.
• The findings provide insights into aldehyde coupling reactions on metal surfaces.