The Nature of Chemisorbed CO2 in Zeolite A

Formation of CO32- 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 in situ 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 CO32-. 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.