Modulating acid site spatial location of Zn/ZSM-5 catalyst to boost the stable aromatization of hexane
Engineering acid site spatial location of zeolite catalyst harbors tremendous potential to boost catalytic performance but still remains a grand challenge for aromatization reaction. Herein, we successfully manipulate acid site spatial location inside the ZSM-5 channels to promote the hexane aromatization via the simple SiO 2 coating treatment. Multi-techniques demonstrated that the medium strong L acid in the channel originated from the Si(Al) O Zn structure is mainly retained in the Zn/ZSM-5-Si catalyst by covering the acid sites outside the channel. Surprisingly, there is a good linear relationship between BTEX yield and this medium strong L acid content. Based on the reaction kinetics, in situ FT-IR and theoretical calculations, it is found that the L acid with confinement effect served as the main active site could prominently enhance the cyclization of propene intermediate and the dehydrogenation of cycloalkane due to the strong affinity between the C/H and ZnOx, and control the desorption of BTEX (mainly benzene, toluene, ethylbenzene, and p-xylene) by weakening the binding of hydrogen proton to π electrons. Compared with the ordinary Zn/ZSM-5 catalyst, the yield of BTEX is increased by nearly 10%, and the Zn/ZSM-5-Si catalyst exhibits excellent anti coking deactivation ability. This strategy together with mechanistic results may pave the rational design of efficient Zn/ZSM-5 catalysts for aromatization reaction.
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