4.7 Article

CO2 conversion to cyclic carbonates catalyzed by ionic liquids with aprotic heterocyclic anions: DFT calculations and operando FTIR analysis

Journal

JOURNAL OF CO2 UTILIZATION
Volume 28, Issue -, Pages 66-72

Publisher

ELSEVIER SCI LTD
DOI: 10.1016/j.jcou.2018.09.012

Keywords

CO2 conversion; AHA ionic liquids; FTIR; Reaction mechanism; Propylene carbonate

Funding

  1. Comunidad Autonoma de Madrid [S2013/MAE-2800]
  2. Ministerio de Economia y Competitividad (MINECO) of Spain [CTQ2017-89441-R]

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Quantum chemical calculations and in situ infrared spectroscopy were applied to analyze the role of CO2 activation by aprotic heterocyclic anion ionic liquids (AHA-ILs) in its reaction with propylene oxide to form propylene carbonate. Two AHA-ILs with remarkably different behavior as CO2 chemical absorbent were considered: triethyl(octyl)-phosphonium indazole, [P-2228][Inda], and triethyl(octyl)-phosphonium 2-cyanopyrrol-1-ide [P2228][2-CNPyr]. The structure and energy of reaction intermediates were predicted by Density Functional Theory (DFT) method, observing that CO2 and AHA-IL reaction form an anionic carbamate that promotes a nucleophilic attack on the propylene oxide, causing the ring opening with negligible energy barrier. Later intramolecular cyclization occurs, followed by the AHA-IL regeneration and propylene carbonate production, both requiring appreciable activation energy. The proposed reaction mechanism were experimentally validated by ATR-FTIR measurements, identifying the characteristic signals of reactants, products and intermediate species. Finally, the reaction using the AHA-ILs [P2228][Inda] and [P2228][2-CNPyr] was followed over time using operando ATR-FTIR technique at different operating conditions (temperature and catalyst concentration). A close relationship between the performance of AHA-IL as CO2 chemical absorbent and CO2 conversion catalyst is revealed, opening opportunities for the efficient application of AHA-ILs in intensified process of CO2 capture and utilization.

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