Modification of the Zeolite ZSM‑5 Adsorbent for CO2 Capture.

The rise in greenhouse gas emissions has significantly raised the average global temperature, intensifying the global warming crisis. Addressing this challenge requires substantial efforts from both academia and industry to deliver impactful mitigation solutions. Thus, the development of efficient materials and processes for mitigating greenhouse gases, particularly carbon dioxide (CO2), is of great interest. In this study, various zeolite adsorbents were synthesized, including pristine NH4-ZSM-5, the calcined form H-ZSM-5, and its cation-exchanged variants (Ba-ZSM-5, Mn-ZSM-5, Ni-ZSM-5, and Zn-ZSM-5), and their effectiveness in CO2 capture was tested at different temperatures. All of the adsorbent materials demonstrated decent CO2 capacity, with NH4-ZSM-5 achieving the highest capacity of 1.45 mmol/g at 25 °C and 1 atm under pure CO2 tests. Although the cation-exchange process slightly reduces the CO2 capture capacity under dry conditions, it enhanced the CO2 capacity under humid conditions as compared to the pristine NH4-ZSM-5 material and also improved CO2/N2 selectivity by limiting N2 uptake. The capacity for CO2 adsorption declined with increasing temperature, indicating a physisorption-driven interaction mechanism. Additionally, the materials exhibited rapid adsorption kinetics best described by a pseudo-first-order kinetic model. The adsorbents also showed stable capacity over five adsorption-desorption cycles, indicative of the robustness of the material. Furthermore, unary CO2 and H2O adsorption isotherms, coadsorption uptake of CO2 in the presence of humidity, and CO2 breakthrough experiments under humid conditions relevant to postcombustion CO2 capture scenario were also carried out. X-ray diffraction, Brunauer-Emmett-Teller (BET) surface area analysis, and scanning electron microscopy-energy dispersive X-ray spectroscopy techniques were employed to examine the physicochemical characteristics of the materials. Thus, the development of an efficient CO2 adsorbent with high uptake, rapid kinetics, high selectivity, and excellent thermal stability applying the realistic condition is of paramount importance for future CO2 capture applications.