Synthesis research of nanosized ZSM-5 zeolites in the absence of organic template

Abstract

Nanosized ZSM-5 zeolite was successfully synthesized at 453 K for 24 h after agitating for a duration of 5 h with great speed and 24 h aging in the synthesis sol with the molar composition of 12Na2O:100SiO2:2Al2O3:2500H2O. X-ray diffraction confirmed ZSM-5 crystal phase, transmission electron microscopy showed ZSM-5 zeolite crystal sizes are about 15 nm. Fourier transform infrared analysis further showed that nanosized zeolite has pentacycle of typical absorption summit of ZSM-5 at 546 cm-1. The results clearly show that Na+ cation plays a role of structure directing as well as a role of charge balancing agent. In addition, it is noticed that when the SiO2/Al2O3 molar ratio is 50, higher or lower Na2O content seems unable to obtain pure ZSM-5. Otherwise, as the SiO2/Al2O3 molar ratio decreases to 30 or lower than it, the crystallization tends to direct toward the formation of mordenite. The results show that synthesis temperature and time, concentration, agitation and aging are very important in preparing nanosized ZSM-5 zeolite. © 2007 Elsevier B.V. All rights reserved.