CO2 Capture and In Situ Conversion to Methanol in Novel Basic Deep Eutectic Solvents: Performance and Mechanism

To overcome the high energy consumption associated with conventional CO 2 capture and conversion processes, this study develops an integrated strategy combining CO 2 capture and in situ hydrogenation to methanol using a novel basic deep eutectic solvent (DES). The DES, composed of N,N,N ′ ,N ′ -tetraethylethylenediamine (TEEDA) as a hydrogen bond acceptor and ethylene glycol (EG) as a hydrogen bond donor (optimal molar ratio 1:20), serves as both a capture medium and a reaction promoter. When coupled with a commercial Cu/ZnO/Al 2 O 3 catalyst, the system achieved efficient CO 2 capture (1.14 mmol·g –1 ) and direct in situ conversion. Under optimized conditions (240 ° C, 8 MPa H 2 , 12 h), a methanol selectivity of 92.9% with a yield of 72.5% was attained; even at 180 ° C, a selectivity of 96.0% with a yield of 57.5% was obtained. Control experiments confirmed that the polar EG solvent enhances CO 2 conversion through solvation effects, while the DES itself possesses no intrinsic catalytic activity. Mechanistic studies indicate that CO 2 is captured via the formation of alkyl carbonate ions, and subsequent hydrogenation proceeds through a formate pathway. Density functional theory (DFT) calculations further demonstrate that the polar DES environment reduces the activation energy barrier for the rate-limiting H 2 heterolysis step. The DES showed good recyclability over four cycles, and catalyst deactivation was primarily attributed to sintering-induced loss of Cu surface area. This work presents a viable DES-based integrated process for CO 2 capture and valorization, highlighting the solvent’s dual function and providing insights into the design of efficient integrated capture–conversion systems.