Study of Carbon Dioxide Adsorption on Mesoporous Aminopropylsilane-Functionalized Silica and Titania Combining Microcalorimetry and in Situ Infrared Spectroscopy

Abstract

Two calcined mesoporous supports, silica and titania, were functionalized with aminopropylsilane (APS). The samples were characterized using ATR (attenuated total reflectance), nitrogen sorption at 77 K, and thermogravimetric analysis. The functionalized silica and titania are mesoporous and were grafted with 1.4 and 1.6 molecules of APS per nm2, respectively. Infrared measurements propose that the properties of the amine sites are affected by the chemical properties of the support. For example, the NH2 bending vibration δ(NH) was shifted to lower wavenumbers from 1597 to 1575 cm−1 from the silica to the titania grafted sample, respectively. This could be explained by different interactions with the surface hydroxyl groups of silica and titania. The grafted samples were investigated for carbon dioxide adsorption by combining microcalorimetry and in situ FTIR spectroscopy. Their CO2 adsorption properties are presented in comparison to the nongrafted support materials. Microcalorimetric measurements show important enthalpies of adsorption at low CO2 coverage (more than −80 kJ mol−1) for the APS-grafted materials, indicating a strong reactivity between carbon dioxide and the amine sites. In situ infrared spectroscopy was used to study this reactivity. The formation of three products (carbamate, carbamic acid, and bidentate carbonate) is proposed.