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

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.