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.