The Nature of Chemisorbed CO2 in Zeolite A

Formation of CO₃^2- and HCO₃^- species without participation of the framework oxygen atoms upon chemisorption of CO₂ in zeolite |Na₁₂|-A is revealed. The transfer of O and H atoms is very likely to have proceeded via the involvement of residual H₂O or acid groups. A combined study by solid-state ¹³C MAS NMR, quantum chemical calculations, and <i>in situ</i> IR spectroscopy showed that the chemisorption mainly occurred by the formation of HCO₃^-. However, at a low surface coverage of physisorbed and acidic CO₂, a significant fraction of the HCO₃^- was deprotonated and transformed into CO₃^2-. We expect that similar chemisorption of CO₂ would occur for low-silica zeolites and other basic silicates of interest for the capture of CO₂ from gas mixtures.