Interzeolite transformation from H+-type FAU zeolite into pure CHA zeolite via OSDA/seeds-free and steam-assisted conversion process

Abstract

Pure CHA zeolite was transformed from FAU zeolite via organic structure-directing agent (OSDA)/seeds-free steam-assisted conversion (SAC). CHA zeolite was transformed using H+-type FAU zeolite with a low Si/Al ratio (Si/Al = 2.8) and a small amount of potassium hydroxide (KOH) and H2O. The Si/Al ratio of the CHA zeolite of the final product was the same as that of FAU-type zeolite as raw material because OH− ions derived from KOH reacted with H+ ions in FAU zeolite. Then, Si constituting FAU zeolite was little dissolved in a small amount of the basic solvent during the interzeolite transformation process. In general, in the interzeolite transformation process, the Si/Al ratio of the final product is lower than that of zeolite as raw material due to the dissolution of Si in the framework in the basic solvent. However, the interzeolite transformation process in this study can reduce the dissolving Si ratio using H+-type FAU zeolite. In addition, the PHI framework with low CO2 adsorption capacity arose with CHA zeolite transformed from Na+-type FAU zeolite via OSDA-free interzeolite SAC in a previous study. However, in this study, the PHI framework did not arise in OSDA-free steam-assisted interzeolite transformation process due to the use of H+-type FAU zeolite. Furthermore, the second particle morphology of CHA zeolite transformed from H+-type FAU zeolite was spherical, which has not been seen in CHA zeolite particles synthesized in previous reports. Finally, the CO2 adsorption capacity and performance of FAU and CHA zeolites were measured. CHA zeolite showed higher CO2 adsorption capacity than H+-type FAU zeolite as the starting material and high CO2 loadings at low CO2 equilibrium pressure. This study investigated that the synthesis condition, chemical properties, and CO2 adsorption performance of CHA zeolite transformed from H+-type FAU zeolite via the OSDA/seeds-free steam-assisted interzeolite transformation process.