In recent years, the power sector has shown a growing reliance on natural gas, a cleaner-burning fuel than coal that emits approximately half as much CO₂ per kWh of energy produced. This rapid growth in the consumption of natural gas has led to increased CO₂ emissions from gas-fired power plants. To limit the contribution of fossil fuel combustion to atmospheric CO₂ levels, carbon capture and sequestration has been proposed as a potential emission mitigation strategy. However, despite extensive exploration of solid adsorbents for CO₂ capture, few studies have examined the performance of adsorbents in post-combustion capture processes specific to natural gas flue emissions. In this perspective, we emphasize the importance of considering gas-fired power plants alongside coal-fired plants in future analyses of carbon capture materials. We address specific challenges and opportunities related to adsorptive carbon capture from the emissions of gas-fired plants and discuss several promising candidate materials. Finally, we suggest experiments to determine the viability of new CO₂ capture materials for this separation. This broadening in the scope of current carbon capture research is urgently needed to accelerate the deployment of transformational carbon capture technologies.

A series of structurally diverse alcoholamine- and alkoxyalkylamine-functionalized variants of the metal-organic framework Mg₂ (dobpdc) are shown to adsorb CO₂ selectively via cooperative chain-forming mechanisms. Solid-state NMR spectra and optimized structures obtained from van der Waals-corrected density functional theory calculations indicate that the adsorption profiles can be attributed to the formation of carbamic acid or ammonium carbamate chains that are stabilized by hydrogen bonding interactions within the framework pores. These findings significantly expand the scope of chemical functionalities that can be utilized to design cooperative CO₂ adsorbents, providing further means of optimizing these powerful materials for energy-efficient CO₂ separations.

A series of structurally diverse alcoholamine- and alkoxyalkylamine-functionalized variants of the metal-organic framework Mg₂ (dobpdc) are shown to adsorb CO₂ selectively via cooperative chain-forming mechanisms. Solid-state NMR spectra and optimized structures obtained from van der Waals-corrected density functional theory calculations indicate that the adsorption profiles can be attributed to the formation of carbamic acid or ammonium carbamate chains that are stabilized by hydrogen bonding interactions within the framework pores. These findings significantly expand the scope of chemical functionalities that can be utilized to design cooperative CO₂ adsorbents, providing further means of optimizing these powerful materials for energy-efficient CO₂ separations.

Natural gas has become the dominant source of electricity in the United States, and technologies capable of efficiently removing carbon dioxide (CO₂) from the flue emissions of natural gas-fired power plants could reduce their carbon intensity. However, given the low partial pressure of CO₂ in the flue stream, separation of CO₂ is particularly challenging. Taking inspiration from the crystal structures of diamine-appended metal-organic frameworks exhibiting two-step cooperative CO₂ adsorption, we report a family of robust tetraamine-functionalized frameworks that retain cooperativity, leading to the potential for exceptional efficiency in capturing CO₂ under the extreme conditions relevant to natural gas flue emissions. The ordered, multimetal coordination of the tetraamines imparts the materials with extraordinary stability to adsorption-desorption cycling with simulated humid flue gas and enables regeneration using low-temperature steam in lieu of costly pressure or temperature swings.

Carbon capture at fossil fuel-fired power plants is a critical strategy to mitigate anthropogenic contributions to global warming, but widespread deployment of this technology is hindered by a lack of energy-efficient materials that can be optimized for CO₂ capture from a specific flue gas. As a result of their tunable, step-shaped CO₂ adsorption profiles, diamine-functionalized metal-organic frameworks (MOFs) of the form diamine-Mg₂(dobpdc) (dobpdc^4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) are among the most promising materials for carbon capture applications. Here, we present a detailed investigation of dmen-Mg₂(dobpdc) (dmen = 1,2-diamino-2-methylpropane), one of only two MOFs with an adsorption step near the optimal pressure for CO₂ capture from coal flue gas. While prior characterization suggested that this material only adsorbs CO₂ to half capacity (0.5 CO₂ per diamine) at 1 bar, we show that the half-capacity state is actually a metastable intermediate. Under appropriate conditions, the MOF adsorbs CO₂ to full capacity, but conversion from the half-capacity structure happens on a very slow time scale, rendering it inaccessible in traditional adsorption measurements. Data from solid-state magic angle spinning nuclear magnetic resonance spectroscopy, coupled with van der Waals-corrected density functional theory, indicate that ammonium carbamate chains formed at half capacity and full capacity adopt opposing configurations, and the need to convert between these states likely dictates the sluggish post-half-capacity uptake. By use of the more symmetric parent framework Mg₂(pc-dobpdc) (pc-dobpdc^4- = 3,3'-dioxidobiphenyl-4,4'-dicarboxylate), the metastable trap can be avoided and the full CO₂ capacity of dmen-Mg₂(pc-dobpdc) accessed under conditions relevant for carbon capture from coal-fired power plants.

Diamine-appended Mg₂(dobpdc) (dobpdc^4- = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) metal-organic frameworks are a promising class of CO₂ adsorbents, although their stability to SO₂─a trace component of industrially relevant exhaust streams─remains largely untested. Here, we investigate the impact of SO₂ on the stability and CO₂ capture performance of dmpn-Mg₂(dobpdc) (dmpn = 2,2-dimethyl-1,3-propanediamine), a candidate material for carbon capture from coal flue gas. Using SO₂ breakthrough experiments and CO₂ isobar measurements, we find that the material retains 91% of its CO₂ capacity after saturation with a wet simulated flue gas containing representative levels of CO₂ and SO₂, highlighting the robustness of this framework to SO₂ under realistic CO₂ capture conditions. Initial SO₂ cycling experiments suggest dmpn-Mg₂(dobpdc) may achieve a stable operating capacity in the presence of SO₂ after initial passivation. Evaluation of several other diamine-Mg₂(dobpdc) variants reveals that those with primary,primary (1°,1°) diamines, including dmpn-Mg₂(dobpdc), are more robust to humid SO₂ than those featuring primary,secondary (1°,2°) or primary,tertiary (1°,3°) diamines. Based on the solid-state ¹⁵N NMR spectra and density functional theory calculations, we find that under humid conditions, SO₂ reacts with the metal-bound primary amine in 1°,2° and 1°,3° diamine-appended Mg₂(dobpdc) to form a metal-bound bisulfite species that is charge balanced by a primary ammonium cation, thereby facilitating material degradation. In contrast, humid SO₂ reacts with the free end of 1°,1° diamines to form ammonium bisulfite, leaving the metal-diamine bond intact. This structure-property relationship can be used to guide further optimization of these materials for CO₂ capture applications.

Abstract: A series of structurally diverse alcoholamine‐ and alkoxyalkylamine‐functionalized variants of the metal–organic framework Mg2(dobpdc) are shown to adsorb CO2selectively via cooperative chain‐forming mechanisms. Solid‐state NMR spectra and optimized structures obtained from van der Waals‐corrected density functional theory calculations indicate that the adsorption profiles can be attributed to the formation of carbamic acid or ammonium carbamate chains that are stabilized by hydrogen bonding interactions within the framework pores. These findings significantly expand the scope of chemical functionalities that can be utilized to design cooperative CO2adsorbents, providing further means of optimizing these powerful materials for energy‐efficient CO2separations.