The preparation of nano-sized H[Zn, Al]ZSM-5 zeolite and its application in the aromatization of methanol

The preparation of nano-sized H[Zn, Al]ZSM-5 zeolite by direct synthesis procedure and its application in the aromatization of methanol were studied. SEM, XRD, and N2 adsorption–desorption data show that H[Zn, Al]ZSM-5 zeolite was composed of aggregates of 250 nm × 50 nm × 25 nm crystals with about 2.1 nm inter-crystal voids. NH3-TPD, pyridine-FTIR, and UV–Vis spectral analyses were also employed to understand the properties of zeolite catalysts prepared by different methods. TGA results confirmed that the nano-structure was resistant to coke in the reaction. BTX yield and catalytic stability were improved in the conversion of methanol over H[Zn, Al]ZSM-5 zeolite. The BTX yield on H[Zn, Al]ZSM-5 was 48% at 437 °C and weight hourly space velocity of 0.8 h−1, slightly decreasing to 32% after 160 h on stream. The ramping rate in the calcinations significantly affected the acidic and catalytic properties of the zeolite. H[Zn, Al]ZSM-5 calcinated at a rate of 1 °C/min showed less Lewis sites, higher BTX yield, and longer lifetime compared to H[Zn, Al]ZSM-5/T calcinated at a rate of 30 °C/min.

Graphical abstractNano-sized H[Zn, Al]ZSM-5 zeolite was prepared by direct synthesis procedure, presented high conversion of methanol (Cm) and yield of BTX (YBTX) in the aromatization of methanol, and exhibited more stable aromatization performance than H[Zn, Al]ZSM-5/T zeolite made by severe calcinations.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Nano-sized H[Zn, Al]ZSM-5 zeolite was prepared by direct synthesis. ► H[Zn, Al]ZSM-5 showed high BTX yield and long lifetimes in methanol aromatization. ► The nano-structure favored anti-coking. ► The high dispersion of Zn favored stable aromatization. ► Severe calcination tampered the aromatization performance.