Abstract
ZSM-48 and ZSM-22 zeolites with similar Si/Al molar ratio have been treated with alkali to modify the pore structures and acidity, and alkali treated ZSM-22 and ZSM-48 samples have been characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), N2 adsorption/desorption, Nuclear Magnetic Resonance (NMR), NH3-Temperature Programmed Desorption (NH3-TPD) and Pyridine-Fourier Transform Infrared Spectroscopy (Py-FTIR). Characterization results indicate that NaOH treatment could improve the mesoporous structure for both ZSM-22 and ZSM-48. NaOH treatment modifies the acidity of ZSM-22 and ZSM-48 diversely. The n-hexane hydroisomerization performances of Pt supported protonic form ZSM-22 and ZSM-48 (Pt/HZSM-22 and Pt/HZSM-48) bifunctional catalysts have been evaluated in a fixed bed reactor. Catalytic results indicate that catalytic activity and selectivity depend on both pore structure and acidity of zeolites. In comparison of Pt/HZSM-22 and Pt/HZSM-48, Pt/HZSM-22 shows better n-hexane hydroisomerization performance at relatively low temperature (<300 °C), meanwhile, at relatively high temperature (>300 °C) Pt/HZSM-48 exhibits better catalytic performance. Moreover, alkali treated Pt/HZSM-48 could produce more di-branched isomer compared with alkali treated Pt/HZSM-22.
Highlights
With the rapid development of the economy and automobile industry, the requirements for high quality oil products and clean fuel have spontaneously grown
Commercial ZSM-22 (Si/Al 1⁄4 37) with similar Si/Al as assynthesized ZSM-48 was treated by alkali, and both alkali treated ZSM-22 and ZSM-48 have been characterized by X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Nuclear Magnetic Resonance (NMR), N2 adsorption/desorption, NH3-Temperature Programmed Desorption (NH3-TPD) and PyFTIR to investigate their structure and acidity
Alkali treatment will not destroy the structure of ZSM-22 and ZSM-48 at suitable NaOH concentration, while high NaOH concentration will obviously reduce the crystallinity
Summary
With the rapid development of the economy and automobile industry, the requirements for high quality oil products and clean fuel have spontaneously grown. Hydroisomerization catalysts are usually bifunctional catalysts, including two active components of supports (acid sites) and metals (hydrogenation/dehydrogenation sites), where supports provide both acid sites for isomerization and suitable pore structures for shape selectivity, and metals provides hydrogenation/dehydrogenation sites. Noble metals such as Pt are usually chosen as hydrogenation components, due to their excellent ability of avoiding coke formation.[2,3] zeolites such as beta, ZSM-5, ZSM-22, ZSM-23, and ZSM-48 etc. The correlation between pore structure and acidity with the hydroisomerization performances of n-hexane on Pt supported HZSM-22 and HZSM48 have been investigated
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