无机体系中两段晶化法合成ZSM-5分子筛的研究

在无有机模板剂条件下，以水玻璃为硅源采用两段变温晶化法合成了结晶度良好的ZSM-5分子筛。分别考察了低温预晶化时间、高温预晶化时间和体系中NaCl引入量对合成分子筛晶体形貌和晶粒尺寸的影响。采用XRD、SEM和N2吸附-脱附等手段对合成样品进行了物性分析。结果表明：两段控温晶化法可以控制分子筛的晶粒尺寸及分布，低温120 ℃预晶化5 h时，合成样品的晶粒最小；高温180 ℃预晶化4 h时，合成样品的晶粒最小；随着合成体系中NaCl引入量的增加，合成ZSM-5分子筛的晶粒尺寸逐渐减小，同时结晶度也逐渐降低，合成体系最佳的n（NaCl）/n（Al2O3）范围应控制在10~30。

SYNTHESIS OF ZSM-5 ZEOLITE BY A TWO-STEP CRYSTALLIZATION METHOD IN TEMPLATE-FREE SYSTEM

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.