Molecular Basis for the High CO2 Adsorption Capacity in Chabazite Zeolites

Published

November 7, 2014

Author(s)

Trong D. Pham, Matthew Ross Hudson, Craig Brown, Raul F. Lobo

Abstract

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

Citation

ChemSusChem

Volume

7

Issue

11

Pub Type

Journals

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Keywords

neutron diffraction, adsorption, zeolites, CO2 separation

Citation

Pham, T. , Hudson, M. , Brown, C. and Lobo, R. (2014), Molecular Basis for the High CO₂ Adsorption Capacity in Chabazite Zeolites, ChemSusChem, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=916230 (Accessed December 14, 2024)