Kundu Arpan, Sillar Kaido, Sauer Joachim
Humboldt Universität zu Berlin, Institut für Chemie Unter den Linden 6 10099 Berlin Germany
University of Tartu, Institute of Chemistry Ravila 14a 50411 Tartu Estonia.
Chem Sci. 2019 Dec 6;11(3):643-655. doi: 10.1039/c9sc03008e.
We perform Grand Canonical Monte Carlo simulations on a lattice of Mg sites (GCMC) for adsorption of four binary A/B mixtures, CH/N, CO/N, CO/N, and CO/CH, in the metal-organic framework Mg(2,5-dioxidobenzedicarboxylate), also known as CPO-27-Mg or Mg-MOF-74. We present a mean field co-adsorption isotherm model and show that its predictions agree with the GCMC results if the same quantum chemical data are used for Gibbs free energies of adsorption at the individual sites and for lateral interaction energies between the same, A⋯A and B⋯B, and unlike, A⋯B, adsorbed molecules. We use both approaches to test the assumption underlying Ideal Adsorbed Solution Theory (IAST), namely approximating A⋯B interaction energies as the arithmetic mean of A⋯A and B⋯B interaction energies. While IAST works well for mixtures with weak lateral interactions, CH/N and CO/N, the deviations are large for mixtures with stronger lateral interactions, CO/N and CO/CH. Motivated by the theory of London dispersion forces, we propose use of the geometric mean instead of the arithmetic mean and achieve substantial improvements. For CO/CH, the lateral interactions become anisotropic. To include this in the geometric mean co-adsorption model, we introduce an anisotropy factor. We propose a protocol, named co-adsorption mean field theory (CAMT), for co-adsorption selectivity prediction from known (experiment or simulation) pure component isotherms which is similar to the IAST protocol but uses the geometric mean to approximate mixed pair interaction energies and yields improved results for non-ideal mixtures.
我们在镁位点晶格上进行巨正则蒙特卡罗模拟（GCMC），以研究四种二元A/B混合物，即CH/N、CO/N、CO/N和CO/CH，在金属有机框架Mg(2,5 - 二氧代苯二甲酸酯)（也称为CPO - 27 - Mg或Mg - MOF - 74）中的吸附情况。我们提出了一种平均场共吸附等温线模型，并表明如果在各个位点用于吸附吉布斯自由能以及用于相同的A⋯A和B⋯B以及不同的A⋯B吸附分子之间的横向相互作用能的量子化学数据相同，那么该模型的预测结果与GCMC结果一致。我们使用这两种方法来检验理想吸附溶液理论（IAST）的基本假设，即将A⋯B相互作用能近似为A⋯A和B⋯B相互作用能的算术平均值。虽然IAST对于横向相互作用较弱的混合物CH/N和CO/N效果良好，但对于横向相互作用较强的混合物CO/N和CO/CH，偏差较大。受伦敦色散力理论的启发，我们建议使用几何平均值而非算术平均值，并取得了显著改进。对于CO/CH，横向相互作用变得具有各向异性。为了将此纳入几何平均共吸附模型，我们引入了一个各向异性因子。我们提出了一种协议，称为共吸附平均场理论（CAMT），用于根据已知的（实验或模拟）纯组分等温线预测共吸附选择性，该协议与IAST协议类似，但使用几何平均值来近似混合对相互作用能，并且对于非理想混合物能产生更好的结果。
