Carbon Capture from Natural Gas Flue Emissions and Air via (Bi)Carbonate Formation in a Cyclodextrin-Based...

Carbon capture and utilization or sequestration (CCUS) from industrial point sources and direct air capture (DAC) are both necessary to curb the rising atmospheric levels of CO₂. Amine scrubbers, the current leading carbon capture technology, suffer from poor oxidative and thermal stability, limiting their long-term cycling stability under oxygen-rich streams such as air and the emissions from natural gas combined cycle (NGCC) power plants. Herein, we demonstrate that the hydroxide-based cyclodextrin metal-organic framework (CD-MOF) Rb₂CO₃ CD-MOF ST possesses high CO₂ capacities from dry dilute streams at low temperatures and humid streams at elevated temperatures. Additionally, it displays good thermal, oxidative, and cycling stabilities and selective CO₂ capture under mixed gas conditions in dynamic breakthrough experiments. Unexpectedly, under dry, hot conditions, a shift in the CO₂ adsorption mechanism─from reversibly formed bicarbonate to irreversibly formed carbonate─is observed, as supported by gas sorption and spectroscopic studies coupled with density functional theory (DFT) calculations. This mechanistic switch, akin to urea formation in amine-functionalized sorbents, has not been previously reported in a hydroxide-based material and sheds new light on the interplay between bicarbonate and carbonate species during CO₂ capture. Our findings provide valuable insight for the design of next-generation materials containing oxygen-based nucleophiles for carbon capture applications.