Curing of Silanol Defects and Tailoring Hierarchical Porosity in ZSM-5 Using PMMA

This study presents a detailed molecular interpretation of the changes found in the zeolitic matrix when two different templates were used to synthesize nanocrystalline ZSM-5. The two templates used are tetrapropylammonium hydroxide (TPAOH) and polymethyl methacrylate (PMMA). Zeolites produced with PMMA as the structure-directing agent yielded hierarchically porous nanocrystalline ZSM-5. Additionally, these samples displayed less fractured Si–O–Si and Si–O–Al connections than those synthesized with TPAOH. These defective Si–O–Si bonds result in the formation of silanol groups. PMMA can effectively engage with the partially crystallized zeolite precursor solution when PMMA is incorporated into the zeolite framework during the crystallization process. This study specifically focuses on analyzing the structure of hierarchical zeolite, with a particular emphasis on conducting diffraction, spectroscopic, and surface analysis investigations. The crystallinity studies reveal that the synthesized materials correspond to MFI-type zeolites using X-ray diffraction (XRD) analysis and selected area electron diffraction (SAED). Infrared spectroscopy and Raman spectroscopy play a very efficient role in distinguishing between the matrices synthesized, and it is used to provide a detailed interpretation of the cause of the defect in the TPAOH-assisted synthesis method. Furthermore, this work delineates the mesoporous characteristics by examining N2 adsorption isotherms and transmission electron microscope (TEM) images.