Surface Active Ionic Liquids as Catalyst for CO2 Conversion to Propylene Carbonate

The ionic liquid-based electrolytes during their charging process: Movable endpoints of overscreening effect near the electrode interface

HYPOTHESIS

Adding solvents to ionic liquids (ILs) can lead to the suppression of the overscreening effect near an electrode interface. Also, this suppression can be observed in neat ILs by elongating the length of the nonpolar chains on their ions. Most neat ILs, unlike the ideal model, do not exhibit a crowding effect in experiments. Through molecular dynamics (MD) simulations, researchers can model and analyze these systems in order to understand them.

SIMULATIONS

In this study, the dynamic change near the electrode interface of ILs-based electrolytes was investigated using MD simulations. The phenomena observed in MD simulations are generally understandable because factors can attenuate charge densities calculated from these simulations.

FINDINGS

The study findings reveal that both the solvents or nonpolar chains contributed to the formation of nonpolar domains. Also, the microscopic mechanisms and influences of these nonpolar domains were clearly identified. The results are important for real life applications. Some ions form a "point to surface" layer near the electrode of neat ILs. When ILs contain long nonpolar chains, they can suppress the crowding effect through self-assembly behavior. However, when they do not have any chains or short nonpolar chains, it can be difficult to stop the overscreening effect. This means it can become challenging to begin the next stage of the crowding effect.

Environmentally sustainable synthesis of cyclic carbonates from epoxides and CO2 promoted by MCM-41 supported dual imidazolium ionic liquids catalysts

A type of MCM-41 supported dual imidazolium ionic liquids have been synthesized and efficiently used as catalysts in the sustainable chemical conversion of CO2 and epoxides into cyclic carbonates. It was shown that the highest efficiency was achieved in the cycloaddition of a variety of epoxides and CO2 in the presence of the MCM-41@DILSCN solid catalyst under mild conditions. More interestingly, the catalyst was stable, very active, robust, and displayed good recyclability without significant loss of catalytic activity after six consecutive cycles during the process. Overall, the present protocol of synthesizing cyclic carbonates under solvent free conditions using MCM-41@DILSCN is promising for industrial applications.

Advanced Formulations Based on Poly(ionic liquid) Materials for Additive Manufacturing

Innovation in materials specially formulated for additive manufacturing is of great interest and can generate new opportunities for designing cost-effective smart materials for next-generation devices and engineering applications. Nevertheless, advanced molecular and nanostructured systems are frequently not possible to integrate into 3D printable materials, thus limiting their technological transferability. In some cases, this challenge can be overcome using polymeric macromolecules of ionic nature, such as polymeric ionic liquids (PILs). Due to their tuneability, wide variety in molecular composition, and macromolecular architecture, they show a remarkable ability to stabilize molecular and nanostructured materials. The technology resulting from 3D-printable PIL-based formulations represents an untapped array of potential applications, including optoelectronic, antimicrobial, catalysis, photoactive, conductive, and redox applications.

Extensively amino-functionalized graphene captures carbon dioxide

Amino-functionalized graphene demonstrates certain potential to fix carbon dioxide.

Basicity as a Thermodynamic Descriptor of Carbanions Reactivity with Carbon Dioxide: Application to the Carboxylation of α,β-Unsaturated Ketones

The utilization of carbon dioxide as a raw material represents nowadays an appealing strategy in the renewable energy, organic synthesis, and green chemistry fields. Besides reduction strategies, carbon dioxide can be exploited as a single-carbon-atom building block through its fixation into organic scaffolds with the formation of new C-C bonds (carboxylation processes). In this case, activation of the organic substrate is commonly required, upon formation of a carbanion C^-, being sufficiently reactive toward the addition of CO₂. However, the prediction of the reactivity of C^- with CO₂ is often problematic with the process being possibly associated with unfavorable thermodynamics. In this contribution, we present a thermodynamic analysis combined with density functional theory calculations on 50 organic molecules enabling the achievement of a linear correlation of the standard free energy (ΔG⁰) of the carboxylation reaction with the basicity of the carbanion C^-, expressed as the pK_a of the CH/C^- couple. The analysis identifies a threshold pK_a of ca 36 (in CH₃CN) for the CH/C^- couple, above which the ΔG⁰ of the carboxylation reaction is negative and indicative of a favorable process. We then apply the model to a real case involving electrochemical carboxylation of flavone and chalcone as model compounds of α,β-unsaturated ketones. Carboxylation occurs in the β-position from the doubly reduced dianion intermediates of flavone and chalcone (calculated ΔG⁰ of carboxylation in β = -12.8 and -20.0 Kcalmol^-1 for flavone and chalcone, respectively, associated with pK_a values for the conjugate acids of 50.6 and 51.8, respectively). Conversely, the one-electron reduced radical anions are not reactive toward carboxylation (ΔG⁰ > +20 Kcalmol^-1 for both substrates, in either α or β position, consistent with pK_a of the conjugate acids < 18.5). For all the possible intermediates, the plot of calculated ΔG⁰ of carboxylation vs. pK_a is consistent with the linear correlation model developed. The application of the ΔG⁰ vs. pK_a correlation is finally discussed for alternative reaction mechanisms and for carboxylation of other C=C and C=O double bonds. These results offer a new mechanistic tool for the interpretation of the reactivity of CO₂ with organic intermediates.

Hybrid Ionic Liquid–Silica Xerogels Applied in CO2 Capture

The imidazolium-based ionic liquids (ILs) are solvents known for selectively solubilizing CO2 from a gas CH4/CO2 mixture, hence we have produced new hybrid adsorbents by immobilizing two ILs on xerogel silica to obtain a solid–gas system that benefits the ILs’ properties and can be industrially applied in CO2 capture. In this work, the ILs (MeO)3Sipmim.Cl and (MeO)3Sipmim.Tf2N were used at different loadings via the sol–gel process employing a based 1-methyl-3-(3-trimethoxysylilpropyl) imidazolium IL associated to the anion Cl− or Tf2N− as a reactant in the synthesis of silica xerogel. The CO2 adsorption measurements were conducted through pressure and temperature gravimetric analysis (PTGA) using a microbalance. SEM microscopies images have shown that there is an IL limit concentration that can be immobilized (ca. 20%) and that the xerogel particles have a spherical shape with an average size of 20 µm. The adsorbent with 20% IL (MeO)3Sipmim.Cl, SILCLX20, shows greater capacity to absorb CO2, reaching a value of 0.35 g CO2 / g adsorbent at 0.1 MPa (298 K). Surprisingly, the result for xerogel with IL (MeO)3Sipmim.Tf2N shows poor performance, with only 0.05 g CO2 / g absorbed, even having a hydrophobic character which would benefit their interaction with CO2. However, this hydrophobicity could interfere negatively in the xerogel synthesis process. The immobilization of ionic liquids in silica xerogel is an advantageous technique that reduces costs in the use of ILs as they can be used in smaller quantities and can be recycled after CO2 desorption.

Molecular design of ionic liquids as novel non-metal catalysts for the acetylene hydrochlorination reaction

Theoretical prediction of catalytic performance is crucial for the rational design of novel catalysts. In this study, density functional theory (DFT) simulations were carried out to predict the catalytic performance of four ionic liquids (ILs) used as novel non-metal catalysts in the acetylene hydrochlorination reaction, and the obtained catalytic performances were verified via our experimental tests; moreover, both the theoretical and experimental results showed that the catalytic performance of the four IL catalysts followed the order tetraphenylphosphonium bromide (TPPB) > tetraphenylphosphonium chloride (TPPC) > butyltriphenylphosphonium bromide (BuTPPB) ≫ tetraphenylphosphonium tetrafluoroborate (TPPT), and the 15%TPPB/SAC catalyst exhibited efficient catalytic performance when compared with the recently reported non-metal catalysts for the acetylene hydrochlorination reaction. Furthermore, the catalytic mechanisms of the four ILs with different cations and anions were revealed via theoretical Mulliken, partial density of states (PDOS) and electron density difference (EDD) analyses combined with the experimental XPS and XRD characterizations. The results showed that the effects of the anions on the catalytic activity were much significant than those of the cations. A good IL non-metal catalyst for acetylene hydrochlorination would mainly donate electrons to Cl to activate the H-Cl bond, and then, the electrons would be donated back to the IL catalyst in the transition state. This study provides new insights into the design of efficient nonmercuric catalysts for the acetylene hydrochlorination reaction.

Catalytic coupling of CO2 with epoxide by metal macrocycles functionalized with imidazolium bromide: insights into the mechanism and activity regulation from density functional calculations

The cycloaddition of CO2 and epoxide catalysed by metalloporphyrins (IL-M(TPP)) and metallocorroles (IL-M(Cor)) containing imidazolium bromide has been studied extensively using density functional theory calculations. Possible mechanisms and catalytic effects of the hydrogen substitution on the imidazolium ring and the metal replacement in the macrocycles have been investigated. The results showed that the synergistic effect between the electrophilic metal centre and the flexible nucleophilic Br- of the bifunctional catalysts was responsible for the high catalytic activity. The coupling reaction of CO2 and ethylene oxide catalysed by IL-Al(Cor) experiences a free energy barrier of 9.7 kcal mol-1 for the rate-determining ring-opening step, which is much lower than ∼20 kcal mol-1 for that catalysed by IL-Zn(TPP). The metallocorrole-based bifunctional catalyst seems quite promising for the catalytic conversion of CO2 into five-membered heterocyclic compounds.