The capture of low concentration CO2 presents numerous challenges. Here, we report that zinc containing chabazite (CHA) zeolites can realize high capacity, fast adsorption kinetics, and low desorption energy when capturing ca. 400 ppm CO2 . Control of the state and location of the zinc ions in the CHA cage is critical to the performance. Zn2+ loaded onto paired anionic sites in the six-membered rings (6MRs) in the CHA cage are the primary sites to adsorb ca. 0.51 mmol CO2 /g-zeolite with Si/Al=ca. 7, a 17-fold increase compared to the parent H-form. The capacity is increased further to ca. 0.67 mmol CO2 /g-zeolite with Si/Al=ca. 2 due to more paired sites for zinc exchange. Zeolites with double six-membered rings (D6MRs) that orient 6MRs into the cages give enhanced uptakes for CO2 adsorption with zinc exchange. The results reveal that zinc exchanged CHA and several other small pore, cage containing zeolites merit further investigation for the capture of low concentration CO2 .
Keywords: adsorption; carbon capture; physisorbents; small-pore zeolites; zinc.
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