Discerning molecular-level CO2 adsorption behavior in amine-modified sorbents within a controlled CO2/H2O environment towards direct air capture

Sorbents designed for direct air capture (DAC) play a crucial role in the pursuit of achieving net-zero carbon dioxide emissions. This study elucidates CO2 adsorption from dilute, humidified CO2 streams onto an amine-modified benchmark DAC adsorbent via solid-state NMR spectroscopy. Various NMR techniques, including 1D 1H MAS, 13C MAS, 2D 1H–13C HETCOR NMR, and 1H R2 and R1ρ relaxometry reveal the impact of CO2 partial pressure and H2O on CO2 adsorption behavior. We find that CO2 concentration governs the stepwise formation of ammonium carbamate, carbamic acid, and physisorbed CO2, where relative humidity (RH) at a desired low (