Atomic-Scale Revelation of Hydrogen Bond Synergy in Efficient COS Capture by Alkaline DES for Fuel Gas Purification

The clean utilization of industrial fuel gases depends on the effective removal of pollutants such as carbonyl sulfide (COS). Although deep eutectic solvents (DESs) have emerged as potential green absorbents, the molecular-level mechanism governing COS capture and its selectivity over CO2 are still poorly understood. Herein, we integrate molecular dynamics (MD) simulations with spectroscopic validation (FT-IR, 1H NMR) to elucidate the capture mechanism in an alkaline TEAC/DEA DES. We conclude that selectivity is primarily driven by a strong physical affinity for COS over CO2. In a competitive environment, this changes to a −13.2 kJ/mol interaction energy advantage for COS, which corroborates the experimentally observed selectivity of 2.1. This strong, hydrogen-bond-driven physisorption is further enhanced by a synergistic electrostatic contribution from the Cl– anion that promotes mass transport. The excellent COS capacity of the TEAC/DEA DES (88.6 mg/g–1) relative to both neat DEA and its amine-free TEAC/EG analogue experimentally confirms the operative nature of this synergy. The optimal operating window at 50 °C is identified, which balances a 15% increase in initial absorption rate (from 30 °C) with the prevention of COS hydrolysis at higher temperatures. Under these conditions, the DES exhibits stable performance over five cycles and low corrosivity. This work illuminates the COS capture mechanism at the atomic scale, providing a theoretical foundation for rational design of next-generation solvents for fuel gas purification.