Modification of Potassium Chabazites Derived from Fly Ash by Dosing Extra Cations: Promoted CO2 Adsorption Capacities and Fine-Tuned Frameworks

Potassium chabazite (K-CHA), a typical microporous zeolite with excellent CO2 separating properties, was synthesized with waste fly ash and modified via cation dosing treatments using cesium and zinc cations, respectively. The resulting CHAs were analyzed by XRF, XRD, FT-IR, SEM, and N-2 physisorption, whose CO2 adsorption properties were then tested on the reorganized TGA apparatus. It showed from XRF data that cesium and zinc cations were successfully imported in the original K-CHA by cation dosing, but the CHA microstructures and morphologies of K-CHA were perfectly retained as confirmed by XRD, FT-IR, SEM and N-2 physisorption. Since there were still over 9 potassium cations per unit cell in cation dosed Cs-CHA and Zn-CHA, they both maintained the favored properties of K-CHA as "molecular trapdoors". In the following adsorption experiments, the CO2 uptakes of Cs-CHA and Zn-CHA at 333 K and 1 bar, compared with K-CHA, elevated from 1.70 mmol center dot g(-1) to 2.34 and 2.03 mmol center dot g(-1), and the import of zinc cation also presented a positive effect on the adsorption kinetics. Detailed comparisons suggested modifications with cesium and zinc cations fine-tune the CHA complying with different mechanisms, and CHAs modified via cation perform more approvingly than fully ion-exchanged ones, providing us important insights into CHA modifications and applications in practice.