Water Enables Efficient CO Capture from Natural Gas Flue Emissions in an Oxidation-Resistant Diamine-Appended Metal-Organic Framework.

Supported by increasingly available reserves, natural gas is achieving greater adoption as a cleaner-burning alternative to coal in the power sector. As a result, carbon capture and sequestration from natural gas-fired power plants is an attractive strategy to mitigate global anthropogenic CO emissions. However, the separation of CO from other components in the flue streams of gas-fired power plants is particularly challenging due to the low CO partial pressure (∼40 mbar), which necessitates that candidate separation materials bind CO strongly at low partial pressures (≤4 mbar) to capture ≥90% of the emitted CO. High partial pressures of O (120 mbar) and water (80 mbar) in these flue streams have also presented significant barriers to the deployment of new technologies for CO capture from gas-fired power plants. Here, we demonstrate that functionalization of the metal-organic framework Mg(dobpdc) (dobpdc = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) with the cyclic diamine 2-(aminomethyl)piperidine (2-ampd) produces an adsorbent that is capable of ≥90% CO capture from a humid natural gas flue emission stream, as confirmed by breakthrough measurements. This material captures CO by a cooperative mechanism that enables access to a large CO cycling capacity with a small temperature swing (2.4 mmol CO/g with Δ = 100 °C). Significantly, multicomponent adsorption experiments, infrared spectroscopy, magic angle spinning solid-state NMR spectroscopy, and van der Waals-corrected density functional theory studies suggest that water enhances CO capture in 2-ampd-Mg(dobpdc) through hydrogen-bonding interactions with the carbamate groups of the ammonium carbamate chains formed upon CO adsorption, thereby increasing the thermodynamic driving force for CO binding. In light of the exceptional thermal and oxidative stability of 2-ampd-Mg(dobpdc), its high CO adsorption capacity, and its high CO capture rate from a simulated natural gas flue emission stream, this material is one of the most promising adsorbents to date for this important separation.