title: Mechanisms and kinetics for sorption of CO2 on bicontinuous mesoporous silica modified with n-propylamine.
abstract: We studied equilibrium adsorption and uptake kinetics and identified molecular species that formed during sorption of carbon dioxide on amine-modified silica. Bicontinuous silicas (AMS-6 and MCM-48) were postsynthetically modified with (3-aminopropyl)triethoxysilane or (3-aminopropyl)methyldiethoxysilane, and amine-modified AMS-6 adsorbed more CO(2) than did amine-modified MCM-48. By in situ FTIR spectroscopy, we showed that the amine groups reacted with CO(2) and formed ammonium carbamate ion pairs as well as carbamic acids under both dry and moist conditions. The carbamic acid was stabilized by hydrogen bonds, and ammonium carbamate ion pairs formed preferably on sorbents with high densities of amine groups. Under dry conditions, silylpropylcarbamate formed, slowly, by condensing carbamic acid and silanol groups. The ratio of ammonium carbamate ion pairs to silylpropylcarbamate was higher for samples with high amine contents than samples with low amine contents. Bicarbonates or carbonates did not form under dry or moist conditions. The uptake of CO(2) was enhanced in the presence of water, which was rationalized by the observed release of additional amine groups under these conditions and related formation of ammonium carbamate ion pairs. Distinct evidence for a fourth and irreversibly formed moiety was observed under sorption of CO(2) under dry conditions. Significant amounts of physisorbed, linear CO(2) were detected at relatively high partial pressures of CO(2), such that they could adsorb only after the reactive amine groups were consumed.
authors.affiliation: Department of Materials and Environmental Chemistry, Berzelii Center EXSELENT on Porous Materials, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, Sweden.
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Bacsik
authors.forename: Nanna
authors.initials: N
authors.lastname: Ahlsten
authors.forename: Asraa
authors.initials: A
authors.lastname: Ziadi
authors.forename: Guoying
authors.initials: G
authors.lastname: Zhao
authors.forename: Alfonso E
authors.initials: AE
authors.lastname: Garcia-Bennett
authors.forename: Belén
authors.initials: B
authors.lastname: Martín-Matute
authors.forename: Niklas
authors.initials: N
authors.lastname: Hedin
mesh_terms: D000327:Adsorption; D002245:Carbon Dioxide / Q000737:chemistry*; D007700:Kinetics; D015394:Molecular Structure; D010316:Particle Size; D016062:Porosity; D011437:Propylamines / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D011437:Propylamines; D002245:Carbon Dioxide; D012822:Silicon Dioxide