Multiple adsorption of CO on Na-exchanged Y faujasite: a DFT investigation

One Ca2+ Site in CaNaY Zeolite Can Attach Three CO2 Molecules

To design efficient CO₂ capture materials, it is necessary to ensure a high adsorption capacity. We recently reported that one Na⁺ site in NaY zeolite can attach two CO₂ molecules. However, the process is not suitable for practical use because it proceeds at a low temperature. Here, we present results on CO₂ adsorption on CaNaY zeolites, demonstrating that one Ca²⁺ site can attach three CO₂ molecules. The ν₃(¹³CO₂) mode arising from the natural ¹³C abundance allows for easy infrared monitoring of the processes: it appears at 2298, 2294, and 2291 cm^-1 for the complexes with one, two, and three CO₂ ligands, respectively. The ¹²CO₂ molecules in the polyligand complexes interact vibrationally, leading to the split of the ν₃(¹²CO₂) modes. At ambient temperature, Ca²⁺(CO₂)₂ complexes predominate at >1 mbar CO₂ and triligand species begin to form at 65 mbar. The obtained results show that CaY zeolites can be very effective CO₂ capture materials.

Molar Entropy and Enthalpy of CO Adsorbed in Zeolites as Derived from VTIR Data: Role of Intermolecular Modes

Detailed analysis of recently reported variable-temperature IR (VTIR) spectra of carbon monoxide adsorbed in alkaline zeolites shows how, not only the corresponding values of standard adsorption enthalpy ( Δ H 0 ) and entropy ( Δ S 0 ) can be obtained, but also the thermodynamic values of molar entropy and enthalpy which characterize the adsorbed gas phase. In addition, it is shown that the so obtained molar entropy data can lead to new insights into soft molecular modes, which would be hardly accessible by conventional IR spectroscopic techniques.