Highly Selective Sorption and Separation of CO₂ from a Gas Mixture of CO₂ and CH₄ at Room Temperature by a Zeolitic Organic–Inorganic Ionic Crystal and Investigation of the Interaction with CO₂

Mixed gas cosorption and gas chromatographic investigations demonstrate that a zeolitic organic–inorganic ionic crystal K 2 [Cr 3 O(OOCH) 6 (4-etpy) 3 ] 2 [α-SiW 12 O 40 ]·2H 2 O [ 1 ·2H 2 O] (etpy = ethylpyridine) with a pore diameter of 3.5 Å possesses high separation ability of carbon dioxide (kinetic diameter 3.3 Å) over methane (3.76 Å) at room temperature in the presence of water vapor. Monte Carlo simulation combined with density functional theory calculation suggests that carbon dioxide molecules diffuse into the one-dimensional channels and interact initially with the potassium ions and then with the oxygen atoms of silicododecatungstates, which are confirmed with carbon dioxide sorption enthalpy and in situ IR spectroscopy.