Development of hierarchical nanocrystalline HZSM-5 in the absence of organic template

Full text: The HZSM-5 zeolite was synthesized by hydrothermal method in the absence of organic template and using seeds, aiming to obtain a hierarchical nanocrystalline zeolite HZSM-5. Initially, a precursor solution of ZSM-5 zeolite was prepared, according to the procedure described in literature (Costa e Araujo, 2010), with molar gel composition 100SiO₂ : 12Na₂O: 2Al₂O₃ : 2500H₂O and using sodium aluminate, sodium hydroxide, silica gel and distilled water as reagents. The final solution was pre crystallized under reflux with stirring (400 rpm) at 70°C for 5 hours. Subsequently, the seeds was added in a fixed proportion (10 mol% with regard to the silica content of the gel) and left reacting for functionalizing at room temperature for 1 hour. The final solution was crystallized in a Teflon-lined stainless steel autoclave at 180°C for 27 hours. The solid products were washed with distilled water, dried overnight at 110°C, calcined in air at 500°C for 2 hours and ion exchange with a solution of 0.8M NH₄NO₃ . This process was repeated for each of the seeds used (commercial zeolite MFI-60, not gel silanized and silanized gel prepared by using the silanization agent phenylaminopropyltrimethoxysilane (PHAPTMS)). The characterization by X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), argon surface area by the BET method, scanning and transmission electron microscopies (SEM/TEM), evidenced that typical MFI structure was successfully formed. We can observe X-ray diffraction that all samples show the characteristic diffraction pattern of a ZSM-5 zeolite with five well-resolved diffraction peaks indexed as the (101), (200), (051), (151) and (331), related to the MFI structure. Moreover, with the use of the seeds in the synthesis of ZSM-5 was an increase in the S_BET and S_EXT, demonstrating the decrease in the cristal size and the appearance of secondary porosity. Considering the results, we confirm obtaining the HZSM-5 zeolite of hierarchical nanocrystalline. (author)