Lanthanum/Gallium-Modified Zn/ZSM-5 Zeolite for Efficient Isomerization/Aromatization of FCC Light Gasoline

A series of lanthanum (La)/gallium (Ga)-containing Zn/ZSM-5 catalysts with different metal contents were synthesized by the post-synthetic method. All prepared catalysts were well characterized by X-ray diffraction, pyridine-Fourier transform infrared spectroscopy, NH3-temperature-programmed desorption, H2-temperature-programmed desorption, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy. The effect of La/Ga addition on the isomerization/aromatization properties of Zn/ZSM-5 was studied, and the synthesis mechanism was proposed. The catalytic activities reach the maximum in 1% LaZn/ZSM-5 catalyst, and the isomerization/aromatization performance decreased with further increase of La content. Besides, La species is more advantageous than Ga species in olefin reduction and upgrading of light gasoline under the same catalyst composition and process conditions. It was believed that the additions of La and Ga to Zn/ZSM-5 could adjust the acidity of the catalysts and improve the dispersion of zinc species, increase the amounts of [Zn(OH)]+ species, and strengthen the interaction between Zn species and support, thus enhancing the isomerization/aromatization activities and prolonging the service life of the catalysts. The suitable L/B value and the highly dispersed Zn active phases were favorable to the high activities of LaZn/ZSM-5 and GaZn/ZSM-5 catalysts in isomerization/aromatization of FCC light gasoline.