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Chem. J. Chinese Universities ›› 2006, Vol. 27 ›› Issue (5): 929.doi:

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Conversion of n-Octane over Modified Nano-crystallite ZSM-5 Catalyst

ZHANG Pei-Qing 1* , GUO Hong-Chen2, WANG Xiang-Sheng2, GUO Xin-Wen2   

  1. 1. Institute of Applied Catalysis, Yantai University, Yantai 264005, China;
    2. State Key Laboratory of Fine Chemicals; Institute of Industrial Catalysts,
    Dalian University of Technology, Dalian 116012, China
  • Received:1900-01-01 Revised:1900-01-01 Online:2006-05-10 Published:2006-05-10
  • Contact: ZHANG Pei-Qing

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Abstract:

By combining alkaline medium hydrothermal treatment with loading mixed rare earth oxide, zinc oxide(or gallium oxide) on nanoscale ZSM-5(20—50 nm) as the active component, respectively, the modified nanoscale ZSM5 catalysts were prepared, and characterized by TEM, XRF, IR, XRD and so on. The aromatization and isomerization of n-octane were used as the model reactions. The effects of the total acid amount, the acid strength distribution and the molar ratio of L to B acid sites on performance of aromatization and isomerization of the modified nanoscale HZSM-5 catalysts were investigated, and the relationship between acid strength and molar ratio of L to B acid sites and coking was also studied. The results indicate that the decrease of the total acid amount and the reduction of acid strength of the nanoscale HZSM-5 catalysts modified by combining alkaline medium hydrothermal treatment with loading mixed rare earth oxide resulted in weakening aromatization activity, strengthening isomerization activity and improving stability obviously. On the basis of the alkaline medium hydrothermal treatment and loading mixed rare earth oxide, the acid properties of the nanoscale HZSM-5 catalyst were regulated again after loading proper amount of zinc oxide(or gallium oxide), as a result, the total acid amount of catalysts increased, stronger acid sites of the catalysts decreased, the Brnsted acid sites of the catalyst decreased lightly, the Lewis acid sites of the catalyst increased obviously and the molar ratio of L to B acid sites of the catalyst increased. The proper molar ratio of L to B(1.4—1.7) and the synergistic action between Lewis acid sites and Bronsted acid sites made the catalysts have a stronger and more stable aromatization and isomerization activity, the rate of coking of the catalyst declined. The yields of aromatics and isoparaffins in the products over the combining modification nanoscale HZSM-5 catalysts reached about 50% and 30%, respectively, the selectivity of the alkyl-aromatics(mainly C7—C9) and iso-paraffins(mainly C4—C6) with a high Octane Number attained 84% and 80%, respectively.

Key words: Nanoscale HZSM-5 zeolite; n-Octane; Modification; Aromatization; Isomerization

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