Issue 2, 2017

CO2 capture in ionic liquid 1-alkyl-3-methylimidazolium acetate: a concerted mechanism without carbene

Abstract

Ionic liquids (ILs) provide a promising medium for CO2 capture. Recently, the family of ILs comprising imidazolium-based cations and acetate anions, such as 1-ethyl-3-methylimidazolium acetate (EMI+OAc), has been found to react with CO2 and form carboxylate compounds. N-Heterocyclic carbene (NHC) is widely assumed to be responsible by directly reacting with CO2 though NHC has not been detected in these ILs. Herein, a computational analysis of CO2 capture in EMI+OAc is presented. Quantum chemistry calculations predict that NHC is unstable in a polar environment, suggesting that NHC is not formed in EMI+OAc. Ab initio molecular dynamics simulations indicate that an EMI+ ion “activated” by the approach of a CO2 molecule can donate its acidic proton to a neighboring OAc anion and form a carboxylate compound with the CO2 molecule. Analysis of this termolecular process indicates that the EMI+-to-OAc proton transfer and the formation of 1-ethyl-3-methylimidazolium-2-carboxylate occur essentially concurrently. Based on these findings, a novel concerted mechanism that does not involve NHC is proposed for CO2 capture.

Graphical abstract: CO2 capture in ionic liquid 1-alkyl-3-methylimidazolium acetate: a concerted mechanism without carbene

Supplementary files

Article information

Article type
Paper
Submitted
23 Sep 2016
Accepted
25 Nov 2016
First published
29 Nov 2016

Phys. Chem. Chem. Phys., 2017,19, 1361-1368

CO2 capture in ionic liquid 1-alkyl-3-methylimidazolium acetate: a concerted mechanism without carbene

F. Yan, N. R. Dhumal and H. J. Kim, Phys. Chem. Chem. Phys., 2017, 19, 1361 DOI: 10.1039/C6CP06556B

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