First-Principles Prediction of the Critical Role of Superoxide Anions in Oxidative Degradation of Aqueous Amine Solvents for Carbon Dioxide Capture

Oxidative degradation of amine solvents which may cause solvent depletion and hazardous byproduct production presents a significant challenge in carbon dioxide (CO₂) capture processes, but the underlying mechanism still remains uncertain. Herein, we propose a molecular mechanism underlying the oxidative degradation of monoethanolamine (MEA) based on first-principles simulations. Our work demonstrates that the degradation process can be initiated by a superoxide (O₂^–) attack on the α-carbon of protonated MEA (MEAH⁺), accompanied by the liberation of ammonia (NH₃). The subsequent steps involve short-lived reactive intermediates, eventually resulting in the oxidative cleavage of carbon–carbon bond and the creation of experimentally observed single-carbon products. The entire sequence may form a catalytic cycle, including O₂^– regeneration, which persists until the radical electron is transferred to an alternative oxidant. The improved mechanistic understanding not only helps to explain experimental trends but also contributes to the design of amine-based solvents with enhanced resistance to oxidative degradation.