硼和氟掺杂ZSM-5分子筛的制备及其甲醇制丙烯反应性能

Preparation of Boron and Fluorine Doped ZSM-5 Zeolites for Methanol to Propylene Reaction

采用两步水热晶化法,通过在合成体系中加入硼酸、氟化铵、氟硼酸铵,合成出了硼和氟改性的ZSM-5分子筛。利用X射线衍射、氮气吸附-脱附、29Si固体核磁共振波谱、傅里叶变换红外光谱、扫描电子显微镜以及NH3程序升温脱附等测试手段对样品进行了表征。结果表明:硼和氟掺杂条件下可以合成具有较高结晶度的ZSM-5分子筛,杂原子掺杂提高了分子筛的硅铝比;硼和氟掺杂可以显著降低ZSM-5分子筛的Lewis酸量,但提高了Brφnsted酸量;硼和氟共同作用可以降低ZSM-5分子筛的颗粒尺寸。甲醇制丙烯评价结果显示:较低的Lewis酸量和适宜的Brφnsted酸性有利于提高丙烯选择性和催化剂寿命;NH4BF4改性的ZSM-5分子筛(Z5-BF2)表现出较高的丙烯选择性和较长的催化剂寿命。

A series of boron and/or fluorine containing ZSM-5 zeolites were synthesized and used for the methanol to propylene(MTP)reaction.The as-synthesized ZSM-5 were characterized by X-ray diffraction,N2 adsorption-desorption,29 Si solid nuclear magnetic resonance,Fourier transform infrared spectroscopy,scanning electron micro-scope,and ammonia temperature-programmed desorption methods.The ZSM-5 molecular sieve with higher crystal-linity can be synthesized under the conditions of boron and fluorine doping.The heteroatom doping improves the SiO2/Al2O3 ratio(nSiO2/nAl2O3)of the molecular sieve.Boron and fluorine doped ZSM-5 possessed reduced Lewis acid sites but increased Br?nsted acid sites.Besides,the particle size of ZSM-5 decreased with both boron and fluorine doping.In the MTP reaction,the enhanced catalyst lifetime could be attributed to the low content of Lewis acid sites and less strong Brφnsted acid sites on the ZSM-5 catalysts.NH4BF4 modified ZSM-5 catalyst(Z5-BF2)with reduced Lewis acid sites and appropriate Brφnsted acid sites exhibited relatively high propylene selectivity and long catalyst lifetime.