摘要
采用预晶化液添加法,即将高温(190oC)预晶化液添加到低温(150oC)晶化母液中合成沸石分子筛,考察了高温预晶化液的Na2O:SiO2比、预晶化时间以及低温晶化母液的Na2O:SiO2比对ZSM-5与丝光沸石之间转晶的影响,并采用X射线衍射和扫描电子显微镜对合成的产物进行了表征.研究发现,通过调节整体合成液的Na2O:SiO2比可有效控制ZSM-5沸石与丝光沸石之间的转晶.当整体合成液的组成为xNa2O:100SiO2:2.5Al2O3:12SO42?:4000H2O时,Na2O:SiO2=0.18是ZSM-5沸石和丝光沸石的一个分界线.通过调节母液的Na含量,使Na2O:SiO2>0.18时,高温预晶化过程中产生MFI结构的晶体在低温晶化时可向丝光沸石发生转晶;当Na2O:SiO2≤0.18时,具有MFI和丝光沸石结构共生的晶体在低温晶化时向MFI结构的ZSM-5沸石发生转晶.ZSM-5与丝光沸石之间转晶的前提条件是高温预晶化所形成晶体的结晶度不能太高(≤30%).另外,整体合成液中Na2O含量对生成晶体的形貌也有影响.
Zeolite crystals were synthesized at a lower temperature （150℃） by adding a nucleation solution prepared at higher temperature （190 ℃） to the mother solution. The effects of the Na20/SiO2 ratio, nucleation time of the nucleation solution, and the ratio of Na20/SiO2 ratio in the mother solution on crystal transformation between ZSM-5 and mordenite were investigated. The transformation between zeolite ZSM-5 and mordenite could be controlled effectively by changing the overall Na20/SiO2 ratio in the overall solution. A Na20/SiO2 ratio of 0.18 formed a boundary between ZSM-5 and mordenite phases when the overall solution had a composition of xNa20：100SIO2：2.5A1203： 12SO42-：4000H20. When the Na20/SiO2 ratio was increased higher than 0.18 by altering the composition of the mother solution, the ZSM-5 product formed by nucleation at higher temperature （190 ℃） could be transformed into mordenite crystals during crystallization at lower temperature （150℃）. When the Na20/SiO2 ratio was ≤ 0.18, a product containing both ZSM-5 and mordenite crystals was obtained during nucleation at higher temperature that could be transformed into ZSM-5 crystals during crystallization at lower temperature. A precondition for crystal transformation between ZSM-5 and mordenite was that the crystallinity of the product formed during nucleation at higher temperature must be ≤ 30%.
出处
《催化学报》
SCIE
EI
CAS
CSCD
北大核心
2012年第8期1290-1298,共9页
基金
浙江省科技厅项目(2009R50020)~~
关键词
ZSM-5沸石
无模板剂
丝光沸石
转晶
控制
ZSM-5 zeolite
template-free
mordenite
crystal transformation
controlling
