Monomers from CO2: Superbases as Catalysts for Formate‐to‐Oxalate Coupling

• Published in: ChemSusChem 2021-03, Vol.14 (6), p.1517-1523
• Main Authors: Schuler, Eric, Ermolich, Pavel A., Shiju, N. Raveendran, Gruter, Gert‐Jan M.
• Format: Article
• Language: English
• Subjects: Carbon dioxide; Catalysts; Chemical reduction; CO2 conversion; Coupling; formate coupling; hydrides; Monomers; Oxalic acid; polyester monomers; Reaction time; superbase catalysts
• ISSN: 1864-5631; 1864-564X
• DOI: 10.1002/cssc.202002725

An interesting contribution to solving the climate crisis involves the use of CO2 as a feedstock for monomers to produce sustainable plastics. In the European Horizon 2020 project “OCEAN” a continuous multistep process from CO2 to oxalic acid and derivatives is developed, starting with the electrochemical reduction of CO2 to potassium formate. The subsequent formate‐to‐oxalate coupling is a reaction that has been studied and commercially used for over 150 years. With the introduction of superbases as catalysts under moisture‐free conditions unprecedented improvements were shown for the formate coupling reaction. With isotopic labelling experiments the presence of carbonite as an intermediate was proven during the reaction, and with a unique operando set‐up the kinetics were studied. Ultimately, the required reaction temperature could be dropped from 400 to below 200 °C, and the reaction time could be reduced from 10 to 1 min whilst achieving 99 % oxalate yield. Superbase catalyst! Formate‐to‐oxalate coupling is important for Carbon Capture and Utilization (CCU) processes. To improve this reaction, superbases are introduced as catalysts in moisture‐free conditions, the kinetics and mechanism are studied with a unique operando set‐up, and unprecedented improvements are shown. Reaction temperature is dropped by 200 °C and reaction time is cut ten‐fold whilst achieving 99 % yield.