Synthesis and characterization of bundle-shaped ZSM-22 zeolite via the oriented fusion of nanorods and its enhanced isomerization performance

Abstract ZSM-22 zeolites with needle-shaped, bundle-shaped, as well as bulk-shaped morphologies are prepared by tuning hydrothermal synthesis conditions. These as-synthesized zeolites have similar crystallinity, Si/Al ratios and micropores revealed by XRD, XRF and BET. However, the oriented fusion of nanorods in the bundle-shaped ZSM-22 zeolite leads to the formation of more framework aluminum atoms over T1 + T2 + T3 sites on the 10-membered rings than that of needle-shaped ZSM-22 zeolite as detected by the 27 Al 2D 3Q MAS NMR. The acidity properties determined by Py-FTIR and DMPy-FTIR show that the interfacial effect between the adjacent nanorods can effectively suppress Bronsted acid strength at the pore mouths and external surface. Interestingly, more Lewis acid sites are generated due to the interfacial defects. As a result, the Pt/Z-BUN catalyst with the weaker acidity and high dispersion of Pt exhibits the highest isomerization selectivity due to the more balanced bifunctionality between acid sites and metal sites among the as-prepared catalysts.