Abstract: ZSM-5 with well-defined crystallinity was synthesized by a two-step crystallization method in a template-free system using sodium silicate as a silica source. The effects of the cystallization time at lower temperature and at higher temperature and the effect of introduction of NaCl on crystal morphology and the final crystal size of ZSM-5 were systematically studied. The synthesized samples were investigated using XRD, SEM and N2 adsorption and desorption techniques. The results showed that two-step crystallization method could control the crystal size and size distribution of ZSM-5. The optimum time duration for nucleation at lower temperature and higher temperature were 5 h and 4 h, respectively, under such conditions, the synthesized sample had the smallest grain size. The crystal size of ZSM-5 was decreased by introduction of NaCl. When the range of n（NaCl）/n（Al2O3）was 10-30, the synthesized ZSM-5 had the smaller crystal size and higher crystallinity.

Key words: two-step temperature method, ZSM-5 molacular sieve, template, crystal size