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

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, N-2 adsorption. desorption, Si-29 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 (nSiO(2)/nAl(2)O(3)) of the molecular sieve. Boron and fluorine doped ZSM-5 possessed reduced Lewis acid sites but increased Bronsted 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 Bronsted acid sites on the ZSM-5 catalysts. NH4BF4 modified ZSM-5 catalyst (Z(5)-BF2) with reduced Lewis acid sites and appropriate Bronsted acid sites exhibited relatively high propylene selectivity and long catalyst lifetime.