Unravelling moisture-induced CO2 chemisorption mechanisms in amine-modified sorbents at the molecular scale


This work entails a comprehensive solid-state NMR and computational study of the influence of water and CO2 partial pressures on the CO2-adducts formed in amine-grafted silica sorbents. Our approach provides atomic level insights on hypothesised mechanisms for CO2 capture under dry and wet conditions in a tightly controlled atmosphere. The method used for sample preparation avoids the use of liquid water slurries, as performed in previous studies, enabling a molecular level understanding, by NMR, of the influence of controlled amounts of water vapor (down to ca. 0.7 kPa) in CO2 chemisorption processes. Details on the formation mechanism of moisture-induced CO2 species are provided aiming to study CO2 : H2O binary mixtures in amine-grafted silica sorbents. The interconversion between distinct chemisorbed CO2 species was quantitatively monitored by NMR under wet and dry conditions in silica sorbents grafted with amines possessing distinct bulkiness (primary and tertiary). Particular attention was given to two distinct carbonyl environments resonating at delta(C) similar to 161 and 155 ppm, as their presence and relative intensities are greatly affected by moisture depending on the experimental conditions. 1D and 2D NMR spectral assignments of both these C-13 resonances were assisted by density functional theory calculations of H-1 and C-13 chemical shifts on model structures of alkylamines grafted onto the silica surface that validated various hydrogen-bonded CO2 species that may occur upon formation of bicarbonate, carbamic acid and alkylammonium carbamate ion pairs. Water is a key component in flue gas streams, playing a major role in CO2 speciation, and this work extends the current knowledge on chemisorbed CO2 structures and their stabilities under dry/wet conditions, on amine-modified solid surfaces.



subject category

Chemistry, Physical; Energy & Fuels; Materials Science, Multidisciplinary


Sardo, M; Afonso, R; Juzkow, J; Pacheco, M; Bordonhos, M; Pinto, ML; Gomes, JRB; Mafra, L

our authors


This work was developed in the scope of project CICECO-Aveiro Institute of Materials from the University of Aveiro ref. UIDB/50011/2020 & UIDP/50011/2020, project CERENA ref. UIDB/04028/2020 & UIDP/04028/2020. We also acknowledge funding from projects ref. PTDC/QUI-QFI/28747/2017 (GAS2MAT-DNPSENS - POCI-01-0145-FEDER-028747), PTDC/QUI-QFI/31002/2017 (SILVIA - CENTRO-01-0145-FEDER-31002), PTDC/QEQ-QAN/6373/2014 and Smart Green Homes POCI-01-0247-FEDER-007678, a co-promotion between Bosch Termotecnologia S.A. and the University of Aveiro. These projects are financed through FCT/MEC and co-financed by FEDER under the PT2020 Partnership Agreement. The NMR spectrometers are part of the National NMR Network (PTNMR) and are partially supported by Infrastructure Project 022161 (co-financed by FEDER through COMPETE 2020, POCI and PORL and FCT through PIDDAC). This work has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement no. 865974).

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