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Chinese Journal of Polymer Science

, Volume 37, Issue 10, pp 995–1004 | Cite as

Mechanistic Study on the Dominant Promotion Effect of Al-/Ti-/Zr-modifications over the VOx/SiO2 UHMWPE Catalysts

  • Yu-Long Jin
  • Lin Liu
  • Yu-Jie Wang
  • Zhen Liu
  • Bo-Ping LiuEmail author
Article
  • 14 Downloads

Abstract

Recently, we reported the first VOx/SiO2 ethylene polymerization catalyst for making Cl-free UHMWPE, and found the dominant promotion effects of Al-/Ti-/Zr-modifications over this catalyst system (Macromol. Chem. Phys. 2017, 218, 1600443). In this work, density functional theory is applied to investigate the underlying mechanism of this remarkable promotion effect of Al-/Ti-/Zr-modifications on a molecular and atomic level. The cluster model with V(III) is found to be the most possible active site due to its lowest overall energy barrier for monomer insertion, though the process of C2H4 coordination and the subsequent formation of transition state are most energy favored for V(II) species. By modifying one of or both V-O-Si in the active model with V-O-M (M = Al, Ti, or Zr), the energy barrier for the binding of the upcoming C2H4 gets lower (particularly for Al- and Zr-modified catalysts), and the transition state also becomes more stable. Generally, the insertion process of C2H4 gets easier after support Al-/Ti-/Zr-modifications. This dominant promotion effect is partially ascribed to the more enriched positive charge distribution on or nearby the V center, and the narrower energy gap between the LUMO of model catalysts and the HOMO of C2H4 for these modified catalysts also contributes much. In addition, the decreased steric hindrance around the V center should be taken into account for the modified models as well. Furthermore, the Brønsted acidity of the catalysts is investigated by introducing a pendent hydroxyl group to the model catalysts, which has a close contact with the V center. Similar promotion effect of support modification by Al, Ti, and Zr could still be observed.

Keywords

Density functional theory Vanadium-oxides Ethylene polymerization Support modification Mechanism 

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Notes

Acknowledgments

This work was financially supported by the National Natural Science Foundation of China (No. 21801079).

Supplementary material

10118_2019_2295_MOESM1_ESM.pdf (333 kb)
Mechanistic Study on the Dominant Promotion Effect of Al-/Ti-/Zr-modifications over the VOx/SiO2 UHMWPE Catalysts

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Copyright information

© Chinese Chemical Society Institute of Chemistry, Chinese Academy of Sciences Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • Yu-Long Jin
    • 1
  • Lin Liu
    • 2
  • Yu-Jie Wang
    • 1
  • Zhen Liu
    • 2
  • Bo-Ping Liu
    • 1
    Email author
  1. 1.College of Materials and EnergySouth China Agricultural UniversityGuangzhouChina
  2. 2.School of Chemical EngineeringEast China University of Science and TechnologyShanghaiChina

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