Effect of magnesium modification over H-ZSM-5 in methanol to propylene reaction

H-ZSM-5-based catalyst is a recognized catalyst which is particularly selective towards the formations of light olefins in the methanol reaction. A series of H-ZSM-5 (SiO 2 /Al 2 O 3 = 38) modified with different amounts of magnesium have been investigated. All the samples were characterized by X-ray diffraction instrument (XRD), temperature-programmed desorption of NH 3 (NH 3 -TPD) and Fourier Transform Infrared Spectoscopy (FT-IR). The results indicated that the impregnation of H-ZSM-5 (SiO 2 /Al 2 O 3 = 38) zeolite with various magnesium loading amount significantly affected the strength of acid sites and decreased the concentration of both weak and strong acid sites. As a result of modification, magnesium mainly interacted with strong Brønsted acid sites, thus generated new medium strong acid sites and enhanced the yield of propylene. The optimum acid property for methanol to propylene (MTP) reaction was gotten over 4.0 Mg-ZSM-5 (4.0 wt% Mg) zeolite catalyst. The maximum yield of propylene was 10.62 wt% over 4.0 Mg-ZSM-5 zeolite catalyst by the 30 min on stream. Coke which was mostly formed on strong Brønsted acid sites, would cause the catalysts deactivation, so the reduction of strong Brønsted acid sites could enhance the catalytic stability.