Mechanistic Insights into Electroreductive C-C Coupling between CO and Acetaldehyde into Multicarbon Products

Area of Science:

• Electrochemistry
• Catalysis
• Organic Chemistry

Background:

• Electrochemical reduction of carbon dioxide (CO2RR) and carbon monoxide (CORR) offers a sustainable route to valuable multicarbon (C3+) products.
• A significant knowledge gap exists in understanding the mechanisms for carbon-carbon coupling beyond simple CO self-coupling, hindering the efficient synthesis of desired products.

Purpose of the Study:

• To elucidate the C-C coupling mechanism between CO and acetaldehyde, a crucial intermediate in CO2RR and CORR.
• To investigate the contribution of CO-acetaldehyde coupling versus CO self-coupling in 1-propanol formation during CORR.

Main Methods:

• Combined isotopic labeling studies to trace reaction pathways.
• In situ spectroscopic investigations to monitor intermediates and reaction dynamics.
• Electrochemical experiments varying reactant concentrations.

Main Results:

• CO directly attacks the carbonyl carbon of acetaldehyde during the C-C coupling reaction.
• The carbon atom from CO is incorporated into the hydroxymethyl group of the resulting 1-propanol.
• While CO-acetaldehyde coupling contributes to 1-propanol formation (up to 36%), CO self-coupling is the predominant pathway.

Conclusions:

• The adsorbed methylcarbonyl intermediate is proposed as a branching point for C2 and C3 product formation.
• This intermediate can be hydrogenated to acetaldehyde and ethanol or undergo further coupling with CO to yield 1-propanol.
• Understanding these mechanisms is crucial for optimizing electrocatalysts for selective C3+ product synthesis.