Oxidative degradation of silica-supported polyethylenimine for CO2 adsorption: insights into the nature of deactivated species

The oxidative degradation of polyethylenimine-impregnated mesoporous SBA-15 silica for CO2 capture was investigated at the molecular level. The adsorbents were exposed to flowing air at different temperatures, and their degree of deactivation was evaluated through the measurement of CO2 adsorption capacity prior and subsequent to air exposure. A solvent-extraction method was employed to isolate the deactivated species from the silica support. The extracted species were investigated by a variety of 1D and 2D NMR techniques such as C-13, H-1, H-1-N-15 HMBC, H-1-C-13 HMQC, and H-1-C-13 HMBC. This in-depth investigation showed that they contain predominantly fragments involving imine and carbonyl groups. Several structural units were conclusively established.