Precise regulation of CO₂ fixation is imperative to meet the stringent demand for high-purity carbamates in integrated CO₂ capture and utilization (ICCU) technologies. While deep eutectic solvents (DESs) offer a tunable platform to circumvent the selectivity limitations of conventional amines, the microscopic origins governing product distribution remain elusive. In this study, in situ ¹³C NMR spectroscopy is employed to elucidate the kinetic evolution and product speciation across a library of amines, establishing a direct correlation between nitrogen substitution and reaction outcomes. The presence or absence of exchangeable hydrogen at the nitrogen site is identified as the master switch for reaction pathways. A distinct hierarchy in absorption kinetics is dictated by this structural variation, following the order: primary > linear secondary > cyclic secondary > tertiary amines. Crucially, a previously unrecognized pathway inversion is triggered by steric hindrance in linear secondary amines, shifting from carbamate dominance to bicarbonate formation at extended reaction times. Guided by these mechanistic insights, a DETA-PZ DES system is engineered, achieving a remarkable CO₂ capacity of 0.51 g/g and a carbamate purity of 90%. This work provides a fundamental theoretical framework linking atomic-level hydrogen bonding environments to macroscopic performance, paving the way for the rational design of next-generation solvents.
 

Amino acids, Deep eutectic solvents, Activated carbon, Flue gas