Rezaeian Mojtaba, Izadyar Mohammad, Nakhaei Pour Ali
Computational Chemistry Research Lab., Department of Chemistry, Faculty of Science , Ferdowsi University of Mashhad , Mashhad , Iran.
J Phys Chem A. 2018 Jul 5;122(26):5721-5729. doi: 10.1021/acs.jpca.8b03152. Epub 2018 Jun 25.
The kinetics and mechanism of CO absorption by ionic liquids (ILs) were studied, theoretically. The studied ILs are composed of 1-ethyl-3-methylimidazolium [Emim] as the cation with a general formula of the [Emim][X] (X = Gly, Ala, Lys, Arg). To investigate the alkyl chain length and the number of the amine group effects on the CO absorption, different amino acid anions were chosen. On the basis of the enthalpy changes during CO capture, a chemisorption nature is confirmed. An increase in the number of amine (-NH) groups in the ILs structures, facilitates the CO absorption. According to kinetic results, the rate of CO absorption by [Emim][Gly] is higher than that of [Emim][Ala]. This can be interpreted by a higher steric hindrance in [Emim][Ala] due to an additional methyl group in the amino acid chain. Donor-acceptor interactions and C-N bond formation were investigated by natural bond orbital analysis. Moreover, topological studies show a covalent nature for the C-N bond critical point that showing CO capture is a chemisorption process. Finally, on the basis of kinetic energy results, donor-acceptor interaction and topological analysis, [Emim][Arg] is proposed as the best candidate for CO absorption from the kinetic and thermodynamic viewpoints.
从理论上研究了离子液体（ILs）吸收CO的动力学和机理。所研究的离子液体由1-乙基-3-甲基咪唑鎓[Emim]作为阳离子，通式为[Emim][X]（X = 甘氨酸、丙氨酸、赖氨酸、精氨酸）。为了研究烷基链长度和胺基数量对CO吸收的影响，选择了不同的氨基酸阴离子。基于CO捕获过程中的焓变，证实了其化学吸附性质。离子液体结构中胺基（-NH）数量的增加有利于CO的吸收。根据动力学结果，[Emim][甘氨酸]吸收CO的速率高于[Emim][丙氨酸]。这可以通过氨基酸链中额外的甲基导致[Emim][丙氨酸]中更高的空间位阻来解释。通过自然键轨道分析研究了供体-受体相互作用和C-N键的形成。此外，拓扑研究表明C-N键临界点具有共价性质，表明CO捕获是一个化学吸附过程。最后，基于动能结果、供体-受体相互作用和拓扑分析，从动力学和热力学观点来看，[Emim][精氨酸]被认为是吸收CO的最佳候选物。
