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Characterization and Modeling of Reversible CO₂ Capture from Wet Streams by a MgO/Zeolite Y Nanocomposite

Signorile, Matteo, Vitillo, Jenny G., D’Amore, Maddalena, Crocellà, Valentina, Ricchiardi, Gabriele, Bordiga, Silvia
Journal of physical chemistry 2019 v.123 no.28 pp. 17214-17224
adsorption, carbon dioxide, carbon dioxide fixation, carbon sequestration, combustion, density functional theory, enthalpy, flue gas, infrared spectroscopy, ions, magnesium, magnesium oxide, models, nanocomposites, sorbents, streams, synergism, temperature, zeolites
The synthesis of CO₂ sorbents capable of working on combustion flue gases is a challenging topic in the field of carbon capture and sequestration. Indeed, the presence of moisture in combustion exhausts makes most of the materials capturing CO₂ through physisorption ineffective, their affinity being larger for H₂O than for CO₂. In this work, we investigate a novel nanocomposite sorbent based on a Mg overexchanged zeolite Y (MgOHY), showing single Mg²⁺ ions and nanoconfined (MgO)ₙ clusters. The interaction of CO₂ with the material is studied thoroughly by combining IR spectroscopy and simulation, comparing dry and wet conditions. IR spectroscopy shows that while in dry conditions the adsorption is mainly driven by the Mg²⁺ ions, in wet ones, the (MgO)ₙ clusters react with carbon dioxide by forming (bi)carbonate-like species. These easily decompose at mild temperatures (25–200 °C). Density functional theory simulations are used to investigate the origin of the CO₂ interaction with representative (MgO)ₙ clusters in the periodic zeolite structure and their enthalpy of formation as a function of the water coverage. The calculations disclose a synergic effect between CO₂ and H₂O that, while favoring the CO₂ fixation, results in the formation of (bi)carbonate-like species less stable than those formed in the absence of water.