Unravelling moisture-induced CO2 chemisorption mechanisms in amine-modified sorbents at the molecular scale
authors Sardo, M; Afonso, R; Juzkow, J; Pacheco, M; Bordonhos, M; Pinto, ML; Gomes, JRB; Mafra, L
nationality International
journal JOURNAL OF MATERIALS CHEMISTRY A
keywords METAL-ORGANIC FRAMEWORKS; CARBON-DIOXIDE CAPTURE; SOLID-STATE NMR; FUNCTIONALIZED MESOPOROUS SILICAS; REACTION-KINETICS; CHEMICAL-SHIFTS; MODIFIED SBA-15; FLUE-GAS; ADSORPTION; WATER
abstract 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.
publisher ROYAL SOC CHEMISTRY
issn 2050-7488
isbn 2050-7496
year published 2021
volume 9
issue 9
beginning page 5542
ending page 5555
digital object identifier (doi) 10.1039/d0ta09808f
web of science category 14
subject category Chemistry, Physical; Energy & Fuels; Materials Science, Multidisciplinary
unique article identifier WOS:000627067700020
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journal impact factor 11.301
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