Synthesis of microscale and nanoscale ZSM-5 zeolites: effect of particle size and acidity of Zn modified ZSM-5 zeolites on aromatization performance
Microscale and nanoscale HZSM-5 zeolites, MZ5 and NZ5, have been successfully synthesized by using a template-free and an in situ seed-induced method, respectively; the synthesized zeolites were then modified by Zn impregnation to obtain Zn-modified catalysts, Zn/MZ5 and Zn/NZ5. Various techniques, including XRD, SEM, 27Al MAS NMR, N2 adsorption, H2-TPR, XPS, NH3-TPD, Py-IR and TG/DTA, were used in the characterization of the catalysts, and their catalytic performance in the aromatization of 1-hexene was investigated to correlate the particle size, acidity and catalytic behavior. Compared to MZ5, the NZ5 sample exhibited better catalytic stability due to its smaller particle size and weaker acid strength. Both Zn-modified catalysts showed increased BTX yield because of the smaller B/L ratio and newly formed stronger Lewis acid sites provided by the [ZnOZn]2+ species, which effectively facilitated the dehydrogenation process in the aromatization. The highest BTX yield of 57.93 wt% was obtained for the Zn/NZ5 sample.