Effect of lanthanum and phosphorus on the aromatization activity of Zn/ZSM-5 in FCC gasoline upgrading

• The introduction of La and P favors the aromatization activity and stability of Zn/ZSM-5.
• The addition of La increases the amount of [Zn(OH)]+ species.
• P addition favors the presence of zinc species located in the channels of HZSM-5.
• ZnLaP/ZSM-5 shows a good prospect for further application in FCC gasoline upgrading.

The effects of La and P addition on the physicochemical properties and the aromatization performance of Zn/ZSM-5 were investigated. The introduction of Zn decreased the amount of Brönsted acid sites and increased that of Lewis acid sites of nanoscale ZSM-5. To improve the yields of aromatics in the aromatization of olefins on bifunctional catalysts, it is necessary to increase the participation of the dehydrogenation reactions in the formation of dienes and the corresponding aromatics from cyclic intermediates in n-octene aromatization. XPS results indicated that the addition of La to Zn/ZSM-5 improves the dispersion of zinc species, strengthens the zinc species-support interaction, increases the amount of [Zn(OH)]+ species, and thus improves the aromatization activity. P addition resulted in the presence of zinc species located in the channels of nanoscale HZSM-5 and enhanced the stability of the catalyst. The synergistic effect of La and P increased the amount of [Zn(OH)]+ species, decreased the loss of zinc species and consequently increased the aromatization activity and the stability of the catalyst. The FCC gasoline upgrading results showed that olefins can be converted into aromatics over ZnLaP/ZSM-5 to compensate the loss of octane number, which suggests a good prospect for application in industry.

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