In-situ synthesis of ultrafine Fe-ZSM-5 zeolite for methanol to propylene (MTP) reaction

Key words:  ultrafine Fe-ZSM-5 zeolite  dry gel conversion  in-situ synthesis  methanol to propylene

Abstract:

Ultrafine Fe-ZSM-5 zeolite containing framework heteroatoms with around 50-120 nm in diameter was successfully in-situ synthesized via a dry gel conversion method. The fabricated samples were characterized by means of XRD, SEM, TEM, UV-Vis, NH₃-TPD, Py-FT-IR and N₂ adsorption-desorption isotherms. The results indicate that Fe source added in-situ can not only reduce the size of zeolite particles, but also reduce the acid strength of zeolite. Ultrafine Fe-ZSM-5 zeolite prepared by in-situ synthesis method contains three kinds of Fe species, and most of Fe attributes to isolated framework Fe³⁺ species in tetrahedral coordination and the rest exists as oligomerized FeO_x and Fe₂O₃ particles. But Fe/ZSM-5 zeolite prepared by impregnation method mainly contains latter two forms of Fe species with a little of Fe³⁺ in the framework of the zeolite. The acid properties of ZSM-5 zeolite were modified by Fe modification, which improved the selectivity of propylene in MTP reaction. Compared to the Fe/ZSM-5 zeolite fabricated by traditional impregnation method, the in-situ synthesized ultrafine Fe-ZSM-5 zeolite containing framework heteroatoms presents higher propylene selectivity in the MTP process due to smaller grain size and more suitable acid properties.