Molecular Basis for the High CO2 Adsorption Capacity in Chabazite Zeolites
Trong D. Pham, Matthew Ross Hudson, Craig Brown, Raul F. Lobo
The structure-property relationship for CO2 adsorption in Li-, Na-, K-CHA (Si/Al = 5 and = 12), and pure silica chabazite (Si-CHA) zeolites was investigated by X-ray and neutron powder diffraction measurements. Two adsorption sites for CO2 were found in all chabazite samples with CO2 adsorption in the 8-membered ring (8MR)being the dominant site where CO2 has a total of 24 close contacts (< 4 A) with framework oxygen atoms. Electric quadrupole-electric field gradient and dispersion interactions drive CO2adsorption at the middle of the (8MR) pore openings, while CO2 polarization due to interaction with accessible cation sites controles the location of CO2 at the second site. Adsorption is dominated by dispersion interactions in Si-CHA where CO2 is observed on the pore walls and at the 8MRs. Li- and Na-CHA-6 have adsorption capacity comparable to low silica commercial faujasite and linde type A at ambient temperature and pressure. The formation of CO2 adsorption complexes on dual cation sites was observed on K-CHA-6 samples due to a higher probability of two K cations bridging a CO2 molecule. Isosteric heats of CO2 adsorption reveal that depending on the cation type, cation concentration, the amount of adsorbed CO2 at the molecular level with the adsorption sites determined from diffraction data. The decrease in the hardness of metal cations Li>Na>K>Cu2+ results in a decrease in the direct interaction of these cations with adsorbate CO2
neutron diffraction, adsorption, zeolites, CO2 separation
, Hudson, M.
, Brown, C.
and Lobo, R.
Molecular Basis for the High CO<sub>2</sub> Adsorption Capacity in Chabazite Zeolites, ChemSusChem, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=916230
(Accessed September 26, 2022)