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One of the possible solutions to prevent global climate change is the reduction of CO2 emissions, which is highly desired for the sustainable development of our society. In this work, the chemical absorption of carbon dioxide in amino acid ionic liquids was studied through first-principles methods. The use of readily accessible and biodegradable amino acids as building blocks for ionic liquids makes them highly promising replacements for the widely applied hazardous aqueous solutions of amines. A detailed insight into the reaction mechanism of the CO2 absorption was obtained through state-of-the-art theoretical methods. This allowed us to determine the reason for the specific CO2 capacities found experimentally. Moreover, we have also conducted a theoretical design of ionic liquids to provide valuable insights into the precise tuning of the energetic and kinetic parameters of the CO2 absorption., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Carbon dioxide-ionic liquid systems are of great current interest, and significant efforts have been made lately to understand the intermolecular interactions in these systems. In general, all the experimental and theoretical studies have concluded so far that the main solute-solvent interaction takes effect through the anion, and the cation has no, or only a secondary role in solvation. In this theoretical approach it is shown that this view is unfounded, and evidence is provided that, similarly to the benzene-CO(2) system, dispersion interactions are present between the solute and the cation. Therefore, this defines a novel site for tailoring solvents to tune CO(2) solubility., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We investigated the key step of Pd-N to Pd-O rearrangement from a model catalytic cycle for the activation of carbon dioxide and methane with static quantum chemical calculations and metadynamics simulation. Our calculations show that different bottlenecks appear in the catalytic cycle but that the investigated rearrangement of the Pd-N to Pd-O bounded complex has a barrier ΔG(#)/ΔF(#) of approximately 20 kJ mol⁻¹ and is therefore accessible at ambient reaction conditions.

Two heterobimetallic Mo,M' complexes (M' = IrIII, RhIII) were synthesized and fully characterized. Their catalytic activity in homogeneous carbon dioxide hydrogenation to formate was studied. A pronounced synergistic effect between the two metals was found, most notably between Mo and Ir, leading to a fourfold increase in activity compared with a binary mixture of the two monometallic counterparts. This synergism can be attributed to spatial proximity of the two metals rather than electronic interactions. To further understand the nature of this interaction, the mechanism of the CO2 hydrogenation to formate by a monometallic IrIII catalyst was studied using computational and spectroscopic methods. The resting state of the reaction was found to be the metal-base adduct, whereas the rate-determining step is the inner-sphere hydride transfer to CO2. Based on these findings, the synergism in the heterobimetallic complex is beneficial in this key step, most likely by further activating the CO2. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs), vary strongly in their interaction with CO2. We suggest simple theoretical approach to predict the CO2 absorption behavior of ILs. Strong interaction of the CO2 with the IL anions corresponds to chemical absorption whereas weak interaction indicates physical absorption. A predictive estimate with a clear distinction between physical and chemical absorption can be simply obtained according to geometries optimized in the presence of a solvation model instead of optimizing it only in gas phase as has been done to date. The resulting Gibbs free energies compare very well with experimental values and the energies were correlated with experimental capacities. Promising anions, for ionic liquids with reversible CO2 absorption properties can be defined by a reaction Gibbs free energy of absorption in the range of −30 to 16 kJ mol−1. [ABSTRACT FROM AUTHOR]

In the reaction of 1-ethyl-3-methylimidazolium acetate [C2C1Im][OAc] ionic liquid with carbon dioxide at 125 °C and 10 MPa, not only the known N-heterocyclic carbene (NHC)-CO2 adduct I, but also isomeric aNHC-CO2 adducts II and III were obtained. The abnormal NHC-CO2 adducts are stabilized by the presence of the polarizing basic acetate anion, according to static DFT calculations and ab initio molecular dynamics studies. A further possible reaction pathway is facilitated by the high basicity of the system, deprotonating the initially formed NHC-CO2 adduct I, which can then be converted in the presence of the excess of CO2 to the more stable 2-deprotonated anionic abnormal NHC-CO2 adduct via the anionic imidazolium-2,4-dicarboxylate according to DFT calculations on model compounds. This suggests a generalizable pathway to abnormal NHC complex formation. [ABSTRACT FROM AUTHOR]

We carried out ab initio molecular dynamic simulations in order to determine the free energy surfaces of two selected reactions including solvents, namely a rearrangement of a ruthenium oxoester in water and a carbon dioxide addition to a palladium complex in carbon dioxide. For the latter reaction we also investigated the gas phase reaction in order to take solvent effects into account. We used two techniques to reconstruct the free energy surfaces: thermodynamic integration and metadynamics. Furthermore, we gave a reasonable error estimation of the computed free energy surface. We calculated a reaction barrier of ΔF = 59:5 ± 8:5 kJ mol-1 for the rearrangement of a ruthenium oxoester in water from thermodynamic integration. For the carbon dioxide addition to the palladium complex in carbon dioxide we found a ΔF = 44:9 ± 3:3 kJ mol-1 from metadynamics simulations with one collective variable. The investigation of the same reactions in the gas phase resulted in ΔF = 24:9 ± 6:7 kJ mol-1 from thermodynamic integration, in ΔF = 26:7±2:3 kJ mol-1 from metadynamics simulations with one collective variable, and in ΔF = 27:1±5:9 kJ mol-1 from metadynamics simulations with two collective variables. [ABSTRACT FROM AUTHOR]

Supportedionic liquid membranes (SILMs) are promising tools for the separationof carbon dioxide from other gases. In this paper, new imidazolium,pyrrolidinium, piperidinium, and morpholinium ionic liquids with atriethylene glycol side chain and tosylate anions, as well as theirsymmetrical dicationic analogues, have been synthesized and incorporatedinto SILMs. The selectivities for CO2/N2andCO2/CH4separations have been measured. Theselectivities exhibited by the dicationic ionic liquids are up totwo times higher than the values of the corresponding monocationicionic liquids. Quantum chemical calculations have been used to investigatethe difference in the interaction of carbon dioxide with monocationicand dicationic ionic liquids. The reason for the increased gas separationselectivity of the dicationic ionic liquids is two-fold: (1) a decreasein permeance of nitrogen and methane through the ionic liquid layer,presumably due to their less favorable interactions with the gases,while the permeance of carbon dioxide is reduced much less; (2) anincrease in the number of interaction sites for the interactions withthe quadrupolar carbon dioxide molecules in the dicationic ionic liquids,compared to the monocationic analogues. [ABSTRACT FROM AUTHOR]

We present a theoretical study of carbene formation from the 1-ethyl-3-methylimidazoliumacetate ionic liquid in the absence and presence of CO2in gas and liquid phase. Although CO2physisorption constitutesa precursory step of chemisorption (the CO2’s reactionwith carbenes, which forms from cations via proton abstraction byanions), it also enables a very stable CO2–anionassociate. However, this counteracts the chemical absorption by reducingthe basicity of the anion and the electrophilicity of the CO2, which is reflected by charge transfer. Accordingly, the observablecarbene formation in the gas phase is hindered in the presence ofCO2. In the neat liquid, the carbene formation is alsosuppressed by the charge screening compared to the case of the gasphase; nevertheless, indications for carbene incidents appear. Interestingly,in the CO2-containing liquid we detect more carbene-likeincidents than in the neat one, which is caused by the way CO2is solvated. Despite the weakness of the CO2–cationinteraction, the CO2–anion associate is distortedby cations, which can be seen in longer associate distances and reduced“binding” energies. While the single solvating anionis shifted away from CO2, many more solvating cations approachit compared to the case of the gas phase. This leads to the conclusionthat while the ionic liquid effect stabilizes charged species, introducingneutral species such as CO2provides an opposite trend,leading to an inverse ionic liquid effect with the facilitation ofcarbene formation and thus of chemical absorption. [ABSTRACT FROM AUTHOR]