Modeling of Substitutional Defects in Magnesium Dichloride Polymerization Catalyst Support

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• 作者：Andrey Bazhenov ; Mikko Linnolahti ; Antti J. Karttunen ; Tapani A. Pakkanen ; Peter Denifl ; Timo Leinonen
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：April 12, 2012
• 年：2012
• 卷：116
• 期：14
• 页码：7957-7961
• 全文大小：474K
• 年卷期：v.116,no.14(April 12, 2012)
• ISSN：1932-7455

文摘

We evaluate methods and models for the periodic quantum chemical treatment of defects in MgCl₂ polymerization catalyst support and demonstrate the applicability of the approach for a study of chemical substitution of chlorine with bromine. Effects of the defects are evaluated through binding of methanol to catalytically relevant MgCl₂ surfaces. Our results show that the hybrid density functional PBE0 method reproduces the MgCl₂ crystal structure in good agreement with experiments and that a triple-味 quality basis set is required to evaluate the donor binding properties. Furthermore, the effects of the defects depend on their position in the crystal lattice, and destabilization of the crystal lattice results in increased donor binding energy. Therefore, substitutions at the coordinatively unsaturated edges typically stabilize the crystallites and lower the donor binding energies, whereas substitutions at the coordinatively saturated bulk typically destabilize the crystallites and increase the donor binding energies. The effects are stronger on the (104) than on the (110) surface. The study is readily extendable to other kinds of defects occurring in crystallites.