Formation of CO<sub>3</sub><sup>2-</sup> and HCO<sub>3</sub><sup>-</sup>
species without participation of the framework oxygen atoms upon chemisorption
of CO<sub>2</sub> in zeolite |Na<sub>12</sub>|-A is revealed. The transfer of O
and H atoms is very likely to have proceeded via the involvement of residual H<sub>2</sub>O
or acid groups. A combined study by solid-state <sup>13</sup>C MAS NMR, quantum
chemical calculations, and <i>in situ</i> IR
spectroscopy showed that the chemisorption mainly occurred by the formation of
HCO<sub>3</sub><sup>-</sup>. However, at a low surface coverage of physisorbed
and acidic CO<sub>2</sub>, a significant fraction of the HCO<sub>3</sub><sup>-</sup>
was deprotonated and transformed into CO<sub>3</sub><sup>2-</sup>. We expect
that similar chemisorption of CO<sub>2</sub> would occur for low-silica
zeolites and other basic silicates of interest for the capture of CO<sub>2</sub>
from gas mixtures.
Frequency-swept adiabatic pulses for broadband solid-state MAS NMR
