Chemisorption of CO on diaminated silica as bicarbonates and different types of carbamate ammonium ion pairs

The chemisorption of CO 2 on aminated silica has a rich chemistry, and its details are important to research in relation to CO 2 capture and catalytic chemistry. In this study, such chemisorption was investigated on aminated and diaminated silica with 1 H and 13 C solid state nuclear magnetic resonance (NMR) spectroscopy under dry and wet conditions. Fast magic-angle spinning (MAS) allowed us to obtain high resolution spectra. Porous silica was modified into a monoaminated version using (3-aminopropyl)triethoxysilane (APTS) and a diaminated one by using 3-(2-aminoethylamino)propyltriethoxysilane (AEAPTS). From the corresponding NMR spectra we could conclude that, under dry conditions, CO 2 chemisorbed as carbamic acid and carbamate ammonium ion pairs and gave similar spectra for both directly-excited 13 C and under cross-polarization (CP) { 1 H} 13 C MAS NMR. Under wet conditions, direct excitation and { 1 H} 13 C CPMAS NMR showed that carbamate ammonium ion pairs formed along with bicarbonates (HCO 3 − ). For the wet conditions, the 13 C and 1 H NMR spectra were especially well resolved, and we could detect two different types of carbamate ammonium ion pairs forming on the diaminated silica. We conclude that carbamate ammonium ion pairs and HCO 3 − moieties can be detected by { 1 H} 13 C MAS NMR, at least qualitatively, in addition to the more time consuming direct excitation. Direct excitation and { 1 H} 13 C-CPMAS NMR allowed detecting carbamate-ammonium ion pairs, carbamic acid and bicarbonate species in amine-modified silica sorbents.