The fourth state of matter drives sustainable carbon upcycling

Converting carbon dioxide from greenhouse gas emissions into valuable organic products is one step toward mitigating the harmful environmental effects of emissions. A team of researchers in the McKelvey School of Engineering at Washington University in St. Louis has shown that carbon monoxide is a more promising starting source for producing organic acids than carbon dioxide.

In research published online Aug. 5 in Green Chemistry, Elijah Thimsen, an associate professor of energy, environmental and chemical engineering, and Alcina Johnson Sudagar, a staff scientist in his lab, explored converting carbon monoxide to two industrially important organic acids using non-thermal atmospheric pressure plasma in aqueous solutions.

Their work highlights the significant increase in oxalic acid and formic acid yields from carbon monoxide compared with carbon dioxide, making the two-step conversion process from carbon dioxide to carbon monoxide and subsequently to organic acids an attractive proposition.

“The plasma-liquid system enhances the reaction conditions, avoiding high pressures and temperatures, and provides a more environmentally friendly method by eliminating the need for catalysts or chemical activators,” Sudagar said. “Our findings help to promote efficient and cost-effective pathways for carbon dioxide fixation and sustainable organic acid production.”

The team discovered that when carbon monoxide reacts in plasma within an aqueous solution, it undergoes the water-gas-shift reaction, yielding dissolved carbon dioxide and hydrogen gas. Organic acids serve as intermediates in this reaction.

“Thermodynamic calculations revealed that the synthesis of organic acids from carbon monoxide is an exothermic and endergonic process, while their decomposition is endothermic and exergonic,” Sudagar said. “Therefore, to maximize the yield of these organic acids, it was essential to decrease the reaction temperatures. Additionally, the production of organic acid intermediates was significantly enhanced under alkaline conditions, indicating a pH-dependent reaction mechanism.”