2025-09-26 ワシントン大学セントルイス校
Researchers in Elijah Thimsen’s lab in the McKelvey School of Engineering has shown that carbon monoxide is a more promising starting source for producing organic acids than carbon dioxide. (Image: Alcina Johnson Sudagar)
＜関連情報＞
- https://source.washu.edu/2025/09/plasma-the-fourth-state-of-matter-drives-sustainable-carbon-upcycling/
- https://pubs.rsc.org/en/content/articlelanding/2025/gc/d5gc02035b
非熱的大気圧プラズマ液体合成法による一酸化炭素からの水溶液中での有機酸の合成 Non-thermal atmospheric pressure plasma–liquid synthesis of organic acids in aqueous solution from carbon monoxide
Alcina Johnson Sudagar, Piper Drebes and Elijah Thimsen
Green Chemistry Published:05 Aug 2025
DOI:https://doi.org/10.1039/D5GC02035B
Abstract
This work aims at understanding the conversion of CO to organic acids, namely oxalic acid and formic acid, using non-thermal atmospheric pressure plasma over aqueous solutions. CO exhibited significantly higher conversion to organic acids (more than 15×) compared to CO2 under the same reaction conditions. The result bolsters a proposed two-step process for CO2 fixation, whereby CO2 is first converted to CO, and then CO is converted to organic acids. The organic acids produced from CO are intermediates in the water–gas shift (WGS) reaction of CO in the presence of an aqueous solution to dissolved CO2 and hydrogen gas. Based on a simple thermodynamic analysis, the organic acid yield was increased by lowering the plasma–liquid reaction temperature using an ice bath to cool the reaction flask. The composition of the organic acids could be varied by changing the pH of the solution. Oxalate was formed in higher concentrations with increasing solution pH above the pKa of the radical species (CO2)˙−. Below the pKa value, formate was the exclusive organic acid formed. The production of formate has a rather weak pH dependence but is enhanced slightly at a basic pH above 10. Furthermore, at basic pH, the effect of electrolyte concentration comes into play. Higher electrolyte concentrations, leading to shorter electrolyte Debye lengths, resulted in lowered organic acid yields. The highest yields of organic acids obtained in our system were 122 mg L−1 for oxalate and 77 mg L−1 for formate at an optimum 1 mM NaOH concentration in the starting solution. This work is a successful pioneering example of CO to organic acids conversion using non-thermal plasmas, which opens the pathway for a promising two-step conversion process of CO2 to organic acids.
