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Unconventional, Highly Selective CO2 Adsorption in Zeolite SSZ-13

Hudson, Matthew R., Queen, Wendy L., Mason, Jarad A., Fickel, Dustin W., Lobo, Raul F., Brown, Craig M.
Journal of the American Chemical Society 2012 v.134 no.4 pp. 1970-1973
adsorption, binding sites, carbon dioxide, copper, gases, heat, nitrogen, zeolites
Low-pressure adsorption of carbon dioxide and nitrogen was studied in both acidic and copper-exchanged forms of SSZ-13, a zeolite containing an 8-ring window. Under ideal conditions for industrial separations of CO₂ from N₂, the ideal adsorbed solution theory selectivity is >70 in each compound. For low gas coverage, the isosteric heat of adsorption for CO₂ was found to be 33.1 and 34.0 kJ/mol for Cu- and H-SSZ-13, respectively. From in situ neutron powder diffraction measurements, we ascribe the CO₂ over N₂ selectivity to differences in binding sites for the two gases, where the primary CO₂ binding site is located in the center of the 8-membered-ring pore window. This CO₂ binding mode, which has important implications for use of zeolites in separations, has not been observed before and is rationalized and discussed relative to the high selectivity for CO₂ over N₂ in SSZ-13 and other zeolites containing 8-ring windows.