Alkali treatment time and SiO2/Al2O3 ratio effects on structural modification to produce micro-mesoporous commercial and synthesized ZSM-5 zeolite catalysts

This research investigated the structural modification by a facile alkali treatment of commercial and synthesized ZSM-5 zeolites. The introduction of mesopores to ZSM-5 structure could improve its catalytic performance in cracking and reforming processes. ZSM-5 samples at SiO2/Al2O3 ratios (60, 100, and 140) were synthesized in a fabricated autoclave reactor. ZSM-5 zeolites were alkali-treated at varying times (0.5–3 h). All ZSM-5 samples were examined using XRD, SEM-EDS, surface area and pore analyzer, and particle size analyzer. The results demonstrated that the pore properties of commercial and synthesized ZSM-5 samples depended on alkali treatment time. The increment of alkali treatment time brought about an increased mesopore surface area and volume for both kinds of ZSM-5 samples, accompanied by a more pronounced type IV isotherm. However, increasing the amount of time for alkali treatment (3 h) resulted in a decrease of mesoporosity in the synthesized ZSM-5 samples. The mesopore formation was a result of preferential dissolution of Si from the synthesized ZSM-5 structure, particularly at higher SiO2/Al2O3 ratios. The alkali-treated synthesized ZSM-5 zeolite at a SiO2/Al2O3 ratio of 140 in 0.2 M NaOH aqueous solution for 1 h exhibited a highly produced mesopore surface area and pore volume, plus the preserved MFI structure.