Department of Chemistry, University of California, Berkeley, California 94720, USA.
1] Department of Chemical and Biological Engineering, University of California, Berkeley, California 94720, USA [2] Department of Chemistry, Zhejiang University, Hangzhou 310027, China.
Nature. 2015 Mar 19;519(7543):303-8. doi: 10.1038/nature14327. Epub 2015 Mar 11.
The process of carbon capture and sequestration has been proposed as a method of mitigating the build-up of greenhouse gases in the atmosphere. If implemented, the cost of electricity generated by a fossil fuel-burning power plant would rise substantially, owing to the expense of removing CO2 from the effluent stream. There is therefore an urgent need for more efficient gas separation technologies, such as those potentially offered by advanced solid adsorbents. Here we show that diamine-appended metal-organic frameworks can behave as 'phase-change' adsorbents, with unusual step-shaped CO2 adsorption isotherms that shift markedly with temperature. Results from spectroscopic, diffraction and computational studies show that the origin of the sharp adsorption step is an unprecedented cooperative process in which, above a metal-dependent threshold pressure, CO2 molecules insert into metal-amine bonds, inducing a reorganization of the amines into well-ordered chains of ammonium carbamate. As a consequence, large CO2 separation capacities can be achieved with small temperature swings, and regeneration energies appreciably lower than achievable with state-of-the-art aqueous amine solutions become feasible. The results provide a mechanistic framework for designing highly efficient adsorbents for removing CO2 from various gas mixtures, and yield insights into the conservation of Mg(2+) within the ribulose-1,5-bisphosphate carboxylase/oxygenase family of enzymes.
碳捕获和封存技术已被提议作为减少大气中温室气体积累的一种方法。如果实施，由于需要从废气流中去除 CO2，燃烧化石燃料的发电厂所产生的电力成本将大幅上升。因此，迫切需要更高效的气体分离技术，例如先进的固体吸附剂可能提供的技术。在这里，我们表明二胺修饰的金属有机骨架可以作为“相变化”吸附剂，具有不寻常的阶跃状 CO2 吸附等温线，其随温度显著变化。光谱、衍射和计算研究的结果表明，尖锐吸附台阶的起源是一种前所未有的协同过程，在该过程中，在依赖于金属的阈值压力以上，CO2 分子插入金属-胺键，导致胺重新组织成具有规则排列的氨基甲酸铵链。因此，可以在较小的温度波动下实现较大的 CO2 分离容量，并且可以实现比最先进的水性胺溶液可实现的再生能量显著降低。这些结果为设计从各种气体混合物中去除 CO2 的高效吸附剂提供了一个机械框架，并为理解核酮糖-1,5-二磷酸羧化酶/加氧酶家族酶中 Mg2+的守恒提供了线索。
