Insights into the Oxidative Degradation Mechanism of Solid Amine Sorbents for CO2 Capture from Air: Roles of Atmospheric Water

Direct air capture (DAC) processes for extraction of CO2 from ambient air are unique among chemical processes in that they operate outdoors with minimal feed pretreatments. Here, the impact of humidity on the oxidative degradation of a prototypical solid supported amine sorbent, poly(ethylenimine) (PEI) supported on Al2O3, is explored in detail. By combining CO2 adsorption measurements, oxidative degradation rates, elemental analyses, solid‐state NMR and in situ IR spectroscopic analysis in conjunction with 18O labeling of water, a comprehensive picture of sorbent oxidation is achieved under accelerated conditions. We demonstrated that the presence of water vapor can play an important role in accelerating the degradation reactions. From the study we inferred the identity and kinetics of formation of the major oxidative products, and the role(s) of humidity. Our data are consistent with a radical mediated autooxidative degradation mechanism. Processes for direct air capture (DAC) of CO2 uniquely operate outdoors in different weather conditions. The oxidative stability of amine‐based sorbents is a critical parameter with economic and environmental impacts on DAC processes. Here we elucidate the impact of ubiquitous atmospheric water vapor on the oxidative stability of DAC sorbents, providing insights into the design of robust sorbents for the practical deployment of DAC technology.