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Nano-Ga/Al-ZSM-5 zeolites are synthesized by the in situ isomorphous substitution method (I-series) and a secondary synthesis method in a Ga­(NO3)3/NH4F solution (S-series). The effects of the Ga incorporation approach on the texture, acidity, and catalytic behavior of 1-hexene aromatization are studied in this work. The reaction stability of the Ga/Al-ZSM-5 catalysts is notably enhanced compared with that of the pristine ZSM-5; this difference is mainly due to the improved mesoporosity and weakened Brønsted acidity. Moreover, the uniform intracrystalline mesopores generated in the secondary synthesized samples effectively promote active GaO+ species in closer proximity to the acidic protons, thus leading to stronger Lewis acid sites (LAS). Therefore, the S-2 sample prepared by secondary synthesis in a high concentration of Ga­(NO3)3/NH4F solution exhibited higher BTX selectivity because of the greater synergic effect and higher dehydrogenation activity of the GaO+/Brønsted acid coordination centers in 1-hexene aromatization.

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The Olefin aromatization is an important method for the upgrade of catalytic cracking (FCC) gasoline and production of fuel oil with high octane number. The nano-ZSM-5 zeolite was synthesized via a seed-induced method, a series of modified nano-ZSM-5 zeolite samples with different Ga deposition amount were prepared by Ga liquid deposition method. The XRD, N2 physical adsorption, SEM, TEM, XPS, H2-TPR and Py-IR measurements were used to characterize the morphology, textural properties and acidity of the modified ZSM-5 zeolites. The catalytic performance of the Hexene-1 aromatization was evaluated on a fixed-bed microreactor. The effects of Ga modification on the physicochemical and catalytic performance of nano-ZSM-5 zeolites were investigated. The Ga species in the modified nano-ZSM-5 zeolites mainly exist as the form of Ga2O3 and GaO+, which provide strong Lewis acid sites. The aromatics selectivity over Ga modified nano-ZSM-5 zeolite in the Hexene-1 aromatization was significantly increased, which could be attributed to the improvement of the dehydrogenation activity. The selectivity for aromatics over the Ga4.2/NZ5 catalyst with suitable Ga deposition amount reached 55.4%.