Zhang Hui, Yang Li-Ming, Ganz Eric
Hubei Key Laboratory of Bioinorganic Chemistry and Materia Medica; Key Laboratory of Material Chemistry for Energy Conversion and Storage, Ministry of Education; Hubei Key Laboratory of Materials Chemistry and Service Failure; School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.
School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, United States.
Langmuir. 2020 Nov 24;36(46):14104-14112. doi: 10.1021/acs.langmuir.0c02750. Epub 2020 Nov 10.
The adsorption properties and formation mechanism of ammonium carbamate for CO capture in '-dimethylethylenediamine (mmen) grafted M(dobpdc) (dobpdc = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate; M = Mg, Sc-Zn, except Ni) have been studied via density functional theory (DFT) calculations. We see that the mmen molecule is joined to the metal site via a M-N bond and has hydrogen bonding with neighboring mmen molecules. The binding energies of mmen range from 135.4 to 184.0 kJ/mol. CO is captured via insertion into the M-N bond of mmen-M(dobpdc), forming ammonium carbamate. The CO binding energies (35.2 to 92.2 kJ/mol) vary with different metal centers. Furthermore, the Bader charge analysis shows that the CO molecules acquire 0.42 to 0.47 |. This charge is mainly contributed by the mmen, and a small additional amount is from the metal atom bonded with the CO. The preferred reaction pathway is a two-step reaction. In the first step, the hydrogen bonded complex B changes into an N-coordinated intermediate D with high barriers (0.69 to 1.58 eV). The next step involves the translation and rotation of the chain in the intermediate D, resulting in the formation of the final O-coordinated product I with barriers of 0.22 to 0.61 eV. The higher barriers of CO reaction with mmen-M(dobpdc) relative to attack the primary amine might be due to the larger steric hindrance of mmen. We hope this work will contribute to an improved understanding and development of future amine-grafted materials for efficient CO capture.
通过密度泛函理论（DFT）计算研究了氨基甲酸铵在'-二甲基乙二胺（mmen）接枝的M（dobpdc）（dobpdc = 4,4'-二氧代联苯-3,3'-二羧酸酯；M = Mg，Sc-Zn，Ni除外）中捕获CO的吸附特性和形成机理。我们发现mmen分子通过M-N键与金属位点相连，并与相邻的mmen分子形成氢键。mmen的结合能范围为135.4至184.0 kJ/mol。CO通过插入mmen-M（dobpdc）的M-N键中被捕获，形成氨基甲酸铵。CO的结合能（35.2至92.2 kJ/mol）随不同的金属中心而变化。此外，Bader电荷分析表明，CO分子获得0.42至0.47 |。该电荷主要由mmen贡献，少量额外电荷来自与CO键合的金属原子。优选的反应途径是两步反应。第一步，氢键复合物B转变为具有高势垒（0.69至1.58 eV）的N配位中间体D。下一步涉及中间体D中链的平移和旋转，导致形成最终的O配位产物I，其势垒为0.22至0.61 eV。与攻击伯胺相比，CO与mmen-M（dobpdc）反应的较高势垒可能是由于mmen的空间位阻较大。我们希望这项工作将有助于更好地理解和开发未来用于高效CO捕获的胺接枝材料。
