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 (13)C, (1)H, (1)H-(15)N HMBC, (1)H-(13)C HMQC, and (1)H-(13)C HMBC. This in-depth investigation showed that they contain predominantly fragments involving imine and carbonyl groups. Several structural units were conclusively established.

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The oxidative degradation of CO2 adsorbents consisting of amine-grafted pore-expanded mesoporous MCM-41 silica was investigated. The adsorbents were treated under flowing air at various temperatures, and the degree of deactivation was evaluated through the measurement of their CO2 adsorption capacity prior and subsequent to exposure to air. To decipher the chemical structure of surface species upon air-deactivation of grafted amines, a solvent extraction procedure was developed using a deuterated basic solution. The obtained solutions were analyzed by a variety of 1D and 2D NMR spectroscopy techniques, such as (29)Si, (13)C, (1)H, [(1)H,(15)N] HMBC, [(1)H,(13)C] HMQC, COSY and DOSY. The surface species generated by oxidative degradation of amine-grafted silica were found to contain functional groups such as imine, amide and carboxylic groups. Several structural units were conclusively demonstrated.

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