Mid-temperature CO₂ Adsorption over Different Alkaline Sorbents Dispersed over Mesoporous Al₂O₃

CO₂ adsorbents comprising various alkaline sorption active phases supported on mesoporous Al₂O₃ were prepared. The materials were tested regarding their CO₂ adsorption behavior in the mid-temperature range, i.e., around 300 °C, as well as characterized via XRD, N₂ physisorption, CO₂-TPD and TEM. It was found that the Na₂O sorption active phase supported on Al₂O₃ (originated following NaNO₃ impregnation) led to the highest CO₂ adsorption capacity due to the presence of CO₂-philic interfacial Al-O^--Na⁺ sites, and the optimum active phase load was shown to be 12 wt % (0.22 Na/Al molar ratio). Additional adsorbents were prepared by dispersing Na₂O over different metal oxide supports (ZrO₂, TiO₂, CeO₂ and SiO₂), showing an inferior performance than that of Na₂O/Al₂O₃. The kinetics and thermodynamics of CO₂ adsorption were also investigated at various temperatures, showing that CO₂ adsorption over the best-performing Na₂O/Al₂O₃ material is exothermic and follows the Avrami model, while tests under varying CO₂ partial pressures revealed that the Langmuir isotherm best fits the adsorption data. Lastly, Na₂O/Al₂O₃ was tested under multiple CO₂ adsorption-desorption cycles at 300 and 500 °C, respectively. The material was found to maintain its CO₂ adsorption capacity with no detrimental effects on its nanostructure, porosity and surface basic sites, thereby rendering it suitable as a reversible CO₂ chemisorbent or as a support for the preparation of dual-function materials.