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Cooperative carbon capture and steam regeneration with tetraamine-appended metal–organic frameworks

Steaming out captured CO2 Although natural gas is less carbon dioxide (CO2)–intensive than coal, capturing its emitted CO2 can be more challenging because combined-cycle natural gas combustion has a CO2 concentration that is only one-third of that of coal combustion and contains high concentrations of oxygen and water. Kim et al. report on a tetraamine-functionalized magnesium metal–organic framework that displays two-step cooperative CO2 adsorption that leads to a high CO2 capacity and adsorption enthalpy (see the Perspective by Peh and Zhao). This material could capture CO2from humid air and could be regenerated with steam, a method that is more economical than temperature or pressure swing methods. Science, this issue p. 392; see also p. 372 Tetraamine-functionalized metal–organic frameworks enable CO2 capture from humid streams, as well as steam regeneration. 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.