CO₂ activation through C-N, C-O and C-C bond formation

Area of Science:

• Chemical Engineering
• Materials Science
• Organic Chemistry

Background:

• Carbon dioxide (CO2) capture remains a critical challenge in mitigating climate change.
• Developing efficient sorbent materials and understanding CO2 chemisorption mechanisms are essential for effective carbon capture technologies.

Purpose of the Study:

• To comparatively model and investigate the chemisorption of CO2 using three distinct reaction pathways: carboxylation, carbonation, and carbamation.
• To evaluate the CO2 uptake capacities of different model substrates activated by 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU).

Main Methods:

• Comparative modeling of CO2 chemisorption via carboxylation (cyclohexanone), carbonation (cyclohexanol), and carbamation (cyclohexylamine).
• Activation of substrates using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU).
• Confirmation of CO2 adduct formation using 13C nuclear magnetic resonance and Fourier-transform infrared spectroscopy.
• Volumetric adsorption measurements and density functional theory (DFT) calculations.

Main Results:

• CO2 fixation was confirmed through enol-CO2 adducts (carboxylation), proton shuttling (carbonation), and self-activation (carbamation).
• Cyclohexanol exhibited the highest CO2 uptake capacity (11.7 mmol CO2 g-1 sorbent), followed by cyclohexylamine (9.3 mmol CO2 g-1 sorbent) and cyclohexanone (8.5 mmol CO2 g-1 sorbent).
• DFT calculations supported the observed trend, indicating a more thermodynamically favorable carbonation process for cyclohexanol.

Conclusions:

• The carbonation of cyclohexanol presents a highly effective pathway for CO2 chemisorption, offering superior uptake capacity compared to carboxylation and carbamation.
• Understanding the distinct reaction mechanisms and thermodynamic favorability is crucial for designing advanced CO2 sorbent materials.