Abstract
Ni-modified ZSM-5 zeolites with different nickel contents were successfully prepared by the in situ synthesis method and the impregnation method. The synthesized samples were characterized by XRD, SEM, N2 adsorption–desorption isothermals, and Py-FTIR. The characterization results show that both the textural properties and crystallization of Ni-modified ZSM-5 zeolites were preserved well, and their acidic properties can be modulated after nickel modification. The corresponding NiMo catalysts supported on Ni-modified ZSM-5 zeolites were prepared by the incipient wetness co-impregnation method, and their catalytic performances were evaluated in n-octane hydroconversion. Compared to the those modified by the in situ synthesis method, ZSM-5 zeolite-supported catalysts modified by the impregnation method exhibit higher stability and higher isomerization selectivity. This is due to the synergistic effect between Brønsted acid sites and Lewis acid sites on the Ni-modified ZSM-5 zeolites, especially for the NiMo/1Ni-Z5 catalyst.
Highlights
Hydrocracking and hydroisomerization are considered crucial processes in the petroleum refining industry, because they could provide a broad range of high-quality chemicals, gasoline, diesel, and petrol
No other phases related with Ni species were observed, indicating the high dispersion of NiO species introduced by the impregnation method on the surface of ZSM-5 zeolites and the existence of framework Ni species on the ZSM-5 zeolites modified by the in situ synthesis method
The incorporation of nickel by the in situ synthesis method into the framework of ZSM-5 zeolites improved the catalytic stability of NiMo/NiZ5 catalysts, a decrease in n-octane conversion and isomerization selectivity were observed. This is because a remarkable decrease of Brønsted acid sites (BAS) would diminish the rate of cracking and isomerization of n-octane when Ni-modified ZSM-5 zeolites were synthesized by the in situ synthesis method
Summary
Hydrocracking and hydroisomerization are considered crucial processes in the petroleum refining industry, because they could provide a broad range of high-quality chemicals, gasoline, diesel, and petrol. ZSM-5 zeolite modification by the in situ synthesized method was denoted as “xNiZ5,” where “x” represents the mass fraction of nickel. The obtained ZSM-5 zeolite was impregnated with an excessive aqueous solution which contains the appropriated mass fraction of nickel. ZSM-5 zeolite modification by the impregnation method was denoted as “xNiZ5,” where “x” represents the mass fraction of nickel. The catalytic performance of Ni-modified ZSM-5 zeolite-supported NiMoS catalysts was evaluated in n-octane cracking reaction. The NiMo catalysts were prepared by the incipient wetness co-impregnation method with an aqueous solution of appropriate amount of nickel nitrate and ammonium metatungstate. The catalytic performance of NiMo catalysts supported on ZSM5 zeolites with different nickel modifications was assessed in a fixed-bed reactor from 275 to 305◦C under H2 at 4.0 MPa, and the weight hourly space velocity (WHSV) was fixed at 4 h−1. Conversion (X), yield (Yi), and selectivity (Si) of product i are calculated according to the following equations (Sun et al, 2020):
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