MFI/MFI核壳分子筛的合成及催化性能研究

Synthesis and Catalytic Behaviors of MFI/MFI Core-shell Zeolite

通过对核相ZSM-5的预处理步骤和在温和水热条件下的二次生长,合成了壳层硅铝比高、核相硅铝比低、纳米晶壳层致密的MFI(核)/MFI(壳)型核壳分子筛材料.考察了晶化温度和晶化时间对高硅壳层MFI/MFI核壳型沸石分子筛的合成的影响,其适宜的合成条件为晶化温度高于130℃,晶化时间19h.核相ZSM-5的预处理步骤对于成功合成此特殊核壳型分子筛材料十分关键.与普通ZSM-5沸石分子筛相比,MFI/MFI核壳分子筛在催化甲苯甲基化反应时的失活效率显著降低.

Hierarchical core/shell structures with low Si/Al ratio core and continuous shell of high Si/Al ra- tio ZSM-5 were successfully fabricated by a novel two-step procedure. The final products were character- ized by X-ray diffraction and scanning electron microscopy （SEM） methods to determine the morphologies and structural properties of the core/shell nanostructures. It was shown that MFI/MFI core-shell zeolite with high Si/Al shell could be synthesized by using ethylamine rather than TPAOH as organic template under mild hydrothermal conditions. It was achieved by in situ pre-seeding step on ZSM-5 cores and secondary growth of ZSM-5 shell on the modified ZSM-5 crystals, in which the pre-seeding step is a determining strategy during the synthesis. The MFI/MFI core-shell zeolite exhibited much lower deactivation rate than the core zeolite in the toluene methylation reaction.