DFT Study on the Chemical Absorption Mechanism of CO₂ in Diamino Protic Ionic Liquids

Abstract

Diamino protic ionic liquids (DPILs) possess a wide application prospect in the field of acid gas absorption. In this work, two representative DPILs, that is, dimethylethylenediamine 4-fluorophenolate ) and dimethylethylenediamine acetate ([DMEDAH][OAc]), which had been proved to display favorable CO 2 absorption performance in experiments, were selected. Based on the solvation model, the different mechanisms of CO 2 absorption by [DMEDAH] + cations combined with different anions were investigated using the dispersioncorrected density functional theory method. Above all, the possible active sites of the reaction between DPILs and CO 2 were analyzed by electrostatic potential (ESP) and electronegativity, and the transition states in each path were searched and verified by frequency calculation and intrinsic reaction coordinate calculation. Furthermore, the Gibbs free energy and reaction heat of each path were calculated, and the free energy barrier and enthalpy barrier diagrams were shown. It was found that the absorption path by the anion of [DMEDAH][4-F-PhO] was favorable in kinetics, while the absorption path by the cation was thermodynamically beneficial. In addition, [DMEDAH][OAc] only showed the possibility of cation absorption, and the mechanism of the transfer of active protons to weak acid anions and the formation of acetic acid molecules was more favorable. Moreover, through the structural analysis, bond order and bond energy calculation, ESP analysis of the ion pair absorption configuration, and comparison with the products of CO 2 absorbed by isolated ions, it was found that the interaction between anions/cations and CO 2 could weaken or enhance the interaction between anions and cations in different reaction steps. Hopefully, this study is helpful to understand the absorption mechanism of CO 2 by DPILs and provides a theoretical basis for the R&D of multi-active site functionalized ILs.

Crystal Facet Structure Dependence and Promising Pd–Pt Catalytic Materials for Perhydroacenaphthene Dehydrogenation

“…From the point of view of physics, Mayer bond order presents the shared electron pairs between two atoms, which can quantitatively reflect the characteristics of chemical bonds and plays an important role in the judgment of chemical bonds. Moreover, Mayer bond order is a physical quantity to judge the strength of chemical bonds; that is, the larger the Mayer bond order, the stronger the bond . The results of the Mayer bond order of dehydrogenation species on the two surfaces are shown in Table and Table S2.…”

“…Moreover, Mayer bond order is a physical quantity to judge the strength of chemical bonds; that is, the larger the Mayer bond order, the stronger the bond. 52 The results of the Mayer bond order of dehydrogenation species on the two surfaces are shown in Table 6 and Table S2. It is seen that Mayer bond order analysis results agree well with those of structural analysis, that is, the average Mayer bond order becomes larger after the whole reaction, and C−C bonds on the whole five-or six-membered ring are enhanced.…”

Tuning Functionalized Ionic Liquids for CO2 Capture

“…Based on the high reactivity of phenolate anions for CO 2 capture, Ye and Li et al [ 135 ] reported that the CO 2 absorption capacities of supported dual functionalized phosphonium ILs [aP 4443 ][2-Op] and [aP 4443 ][2-Np] were 1.57 and 1.88 mol CO 2 per mol IL, respectively, via 2:1 mechanism of amino-CO 2 and 1:1 mechanism of phenolate-CO 2 mechanism. Recently, Wang et al [ 136 ] reported two dual-functionalized protic ILs, dimethylethylenediamine 4-fluorophenolate ([DMEDAH][4-F-PhO]) and dimethylethylenediamine acetate ([DMEDAH][OAc]) to investigate the different chemisorption mechanisms via DFT study. Their results showed that, for [DMEDAH][4-F-PhO], phenolate-CO 2 was favorable in kinetics and amino-CO 2 was thermodynamically beneficial; for [DMEDAH][OAc], amino-CO 2 was favorable with proton-transfer to weak acid anion.…”

Virtual Issue on Carbon Dioxide: Physical Chemistry That Impacts Its Capture, Sequestration, and Conversion

“…Wang and coworkers used density functional theory to construct reaction pathways for CO 2 with diamino protic ionic liquids consisting of a dimethylethylenediamine cation paired with either a 4fluorophenolate or acetate anion. 9 Their calculations suggest that there is a competitive relationship between the anion− cation interaction and the absorption of CO 2 by the anions. Aghaie et al used classical molecular dynamics simulations to study the interactions between water, CO 2 , and the ionic liquid 1-n-butyl-3-methylimidazolium acetate in solution as a function of water concentration.…”

“…The basicity and size of the anion play key roles in the formation of the phosphonium ylide. Wang and co-workers used density functional theory to construct reaction pathways for CO 2 with diamino protic ionic liquids consisting of a dimethylethylenediamine cation paired with either a 4-fluorophenolate or acetate anion . Their calculations suggest that there is a competitive relationship between the anion–cation interaction and the absorption of CO 2 by the anions.…”