Zinc Containing Small-Pore Zeolites for Capture of Low Concentration Carbon Dioxide

Abstract

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.

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