FIRST-PRINCIPLES CALCULATION OF HYDROGEN SENSITIVITY OF DOMESTIC FOURTH-GENERATION ZIEGLER-NATTA CATALYST

Abstract

Abstract: Based on the Density Fundtional Theory(DFT),a Ziegler-Natta catalyst molecular model was established,the adsorption on the catalyst surface was calculated, and the adsorption sites and dominant internal electron donors were studied that can improve the hydrogen modulation sensitivity of the catalyst by simulating the adsorption mechanism. The results show that the Mg atom on the complete MgCl₂ crystal plane is mainly composed of 5 coordinations, without redundant active sites, which is not conducive to the chemical adsorption of TiCl₄. TiCl₄ has chemical adsorption at the single atomic defects on the β crystal (110) crystal plane and the β crystal (100) crystal plane. Among them, the adsorption energy at the single atomic defects on the β crystal (110) surface is generally higher than that at the atomic defects on the β crystal (100) surface, with more charge transfer and more stable adsorption. Although the diatomic defects on the β-crystalline (100) surface can provide more active adsorption sites, the adsorption capacity of the surface for TiC1₄ does not increase accordingly. TiC1₄ is more inclined to adsorb in the single-atom surface defect structure on the (100) surface to form a dichloro bridge. On the β-crystalline (110) surface, the configuration of diatomic defects is more conducive to the adsorption of TiC1₄. The Cl atom in the Ti-Cl bond replaces the Cl atom position in the original complete surface to form a new Mg-Cl bond with the Mg atom, thereby forming an active center. The calculation results of the internal electron donor show that the adsorption energy of diisobutyl phthalate on both surfaces is higher than that of ethyl benzoate, making it more suitable as an internal electron donor for the catalyst.

Key words: Ziegler-Natta catalyst, hydrogen sensitivity, first principles, surface adsorption

References

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