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. Zn 2+ loaded onto paired anionic sites in the sixmembered 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 are worthy of further investigation for the capture of low concentration CO2.

Regulating Extra‐Framework Cations in Faujasite Zeolites for Capture of Trace Carbon Dioxide

“…These values are comparable to that of advanced adsorbents, such as SIFSIX-3-Ni, NbOFFIVE-1-Ni, SIFSIX-18-Ni-β, NaCaÀ A and SIFSIX-3-Cu. (Table S4) [2,4,[17][18][19][22][23][24][25] and thus indicates its great potential in trace CO 2 capture.…”

“…BaÀ X is a transition metals-free sorbent with a highly competitive price of < $3000 per tonne, compared with Zn-CHA and MOFs. [18] The recyclability of these zeolites was also investigated. From the temperature-programmed desorption (TPD) profiles of CO 2 (Figure S20), multiple CO 2 desorption peaks were observed in the temperature range of 323-423 K, indicating the complete removal of adsorbed CO 2 by thermal treatment at > 423 K. For BaÀ X zeolite, thermal regeneration was performed at 423 K, 448 K and 473 K and the CO 2 breakthrough curves (10,000 ppm in synthetic air) were examined.…”

“…Fu et al reported that zinc containing chabazite (CHA) zeolites showed high dynamic uptake of 0.22 mmol g À 1 for 400 ppm CO 2 , unlocking the potential of ion-exchanged zeolites for DAC. [18] Herein, we report a systematic study on capturing trace CO 2 by alkali metals and alkaline earth metals (Li, Na, K, Cs, Mg, Ca, Ba) ion-exchanged faujasite zeolites, aiming to establish the structure-activity relationship to promote the development of practical sorbents for DAC. Under dry conditions, BaÀ X exhibits high dynamic adsorption of CO 2 of 1.79 and 0.69 mmol g À 1 at concentration of 10000 and 1000 ppm, respectively, comparable with state-of-the-art solid adsorbents.…”

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

“…This observation could be attributed to the preferential location of divalent ions inside sodalite (SOD) cages or in the center of the hexagonal prism D6MRs in these materials (Figure S30 with detailed discussion) that are inaccessible to CO2 molecules. [30,63] These results altogether indicate that the framework topology and thus the positioning of extra-framework cations dictate their CO2 adsorption properties. Specifically, the lack of SOD cages and the abundance of accessible 6MRs are two crucial factors for CO2 adsorption in the Zn ion exchanged zeolites.…”

“…Zeolites already have shown promising performance for CO2 capture in postcombustion carbon capture processes as well as CO2 removal in air pre-purification processes (including the international space station, where a desiccant bed is used prior to the zeolite bed for CO2 capture ). [9,23,28,29] Although numerous zeolites have been investigated for carbon capture, [30][31][32][33][34][35] the research for capture of low concentrations of CO2 (ca. 400 ppm) is scarce, and has mainly been focused on low-silica zeolites of the FAU-type (Si/Al less than 2).…”