Modification of the Zeolite ZSM-5 Adsorbent for CO2 Capture

Abstract

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.