Carbonate “door” in the NaKA zeolite as the reason of higher CO2 uptake relative to N2

Theoretical calculations are performed on a model zeolite A where sodium ions have successively been exchanged with potassium. Using both isolated cluster and periodic DFT calculations, we made an attempt to explain how the chemisorbed carbonate species in the material contribute to the exceptionally high CO2 over N2 selectivity of nearly 200 found in recent experiments [Liu et al. [1]] with the zeolite NaKA as adsorbent to capture and separate carbon dioxide from a gas mixture containing nitrogen. We have shown that the high carbonate forming at the potassium positions in the 8R windows (KII) results in a larger 8R window diameter potentially enhancing the CO2 uptake if adsorption is measured for individual gases.

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► The carbonate influence on the alkali cation mobility is first shown.
► Both isolated cluster and periodic modeling is performed.
► Variation of pore size explains unusual measured CO2/N2 separation coefficients.
► Traces of carbonates can require to analyze binary mixture instead of separate gases.