CO2 Capturing Mechanism in Aqueous Ammonia: NH3-Driven Decomposition-Recombination Pathway

Abstract

Capturing CO2 by aqueous ammonia has recently received much attention due to its advantages over other state-of-the-art CO2-capture technology. Thus, understanding this CO2-capturing mechanism, which has been causing controversy, is crucial for further development toward advanced CO2 capture. The CO2 conversion mechanism in aqueous ammonia is investigated using ab initio calculations and kinetic simulations. We show full details of all reaction pathways for the NH3-driven conversion mechanism of CO2 with the pronounced effect of microsolvation. Ammonia performs multiple roles as reactant, catalyst, base, and product controller. Both carbamic and carbonic acids are formed by the ammonia-driven trimolecular mechanism. Ammonia in microsolvation makes the formation of carbamic acid kinetically preferred over carbonic acid. As the concentration of CO2 increases, the dominant product becomes carbonic acid. The conversion from carbamic acid into carbonic acid occurs through the decomposition recombination pathway. This understanding would be exploited for the optimal CO2 capture technology.