title: On the Structure-Property Relationships of Cation-Exchanged ZK-5 Zeolites for CO2Adsorption.
abstract: The CO2adsorption properties of cation-exchanged Li-, Na-, K-, and Mg-ZK-5 zeolites were correlated to the molecular structures determined by Rietveld refinements of synchrotron powder X-ray diffraction patterns. Li-, K-, and Na-ZK-5 all exhibited high isosteric heats of adsorption (Qst) at low CO2coverage, with Na-ZK-5 having the highest Qst(ca. 49 kJ mol-1). Mg2+was located at the center of the zeolite hexagonal prism with the cation inaccessible to CO2, leading to a much lower Qst(ca. 30 kJ mol-1) and lower overall uptake capacity. Multiple CO2adsorption sites were identified at a given CO2loading amount for all four cation-exchanged ZK-5 adsorbents. Site A at the flat eight-membered ring windows and site B/B* in the γ-cages were the primary adsorption sites in Li- and Na-ZK-5 zeolites. Relatively strong dual-cation adsorption sites contributed significantly to an enhanced electrostatic interaction for CO2in all ZK-5 samples. This interaction gives rise to a migration of Li+and Mg2+cations from their original locations at the center of the hexagonal prisms toward the α-cages, in which they interact more strongly with the adsorbed CO2.
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware, 19716, USA.
authors.forename: Trong D
authors.initials: TD
authors.lastname: Pham
authors.affiliation: Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, 20899, USA.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Hudson
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware, 19716, USA.|Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, 20899, USA.
authors.forename: Craig M
authors.initials: CM
authors.lastname: Brown
authors.affiliation: Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware, 19716, USA.
authors.forename: Raul F
authors.initials: RF
authors.lastname: Lobo
mesh_terms: D000327:Adsorption; D002245:Carbon Dioxide / Q000737:chemistry*; D006358:Hot Temperature; D008958:Models, Molecular; D008968:Molecular Conformation; D013329:Structure-Activity Relationship; D017641:Zeolites / Q000737:chemistry*
chemical_list: D017641:Zeolites; D002245:Carbon Dioxide
keywords: CO2; ZK-5; adsorption; diffraction; zeolites