Well-Defined Ti Surface Sites in Ziegler–Natta Pre-Catalysts from ⁴⁷/⁴⁹Ti Solid-State Nuclear Magnetic Resonance Spectroscopy
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2024-03-21
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Journal Article
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yes
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Abstract
Treatment of Ziegler–Natta (ZN) catalysts with BCl3 improves their activity by increasing the number of active sites. Here we show how ⁴⁷/⁴⁹Ti solid-state nuclear magnetic resonance (NMR) spectroscopy enables us to understand the electronic structure of the Ti surface sites present in such treated ZN pre-catalysts, prior to activation with alkyl aluminum. High-field (21.1 T) and low-temperature (∼100 K) NMR augmented by DFT modeling on the pre-catalyst and corresponding molecular analogues enables the detection of ⁴⁷/⁴⁹Ti NMR signatures and a molecular level understanding of the electronic structure of Ti surface sites. The associated Ti surface sites exhibit ⁴⁹Ti NMR signatures (δ_iso, exp = −170 ppm; C_Q, exp = 9.3 MHz; κ = 0.05) corresponding to well-defined fully chlorinated hexacoordinated Ti sites adsorbed on a distorted surface of the MgCl_2 support, formed upon post-treatment with BCl_3 and removal of the alkoxo ligands, paralleling the increased polymerization activity.
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published
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15 (11)
Pages / Article No.
3178 - 3184
Publisher
American Chemical Society
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Subject
Adsorption; Catalysts; Density functional theory; Ligands; Nuclear magnetic resonance spectroscopy
Organisational unit
03872 - Copéret, Christophe / Copéret, Christophe
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Funding
206049 - ZeoNMR (SNF)
192050 - Molecular Approach and Understanding in Heterogeneous Catalysis (SNF)
192050 - Molecular Approach and Understanding in Heterogeneous Catalysis (SNF)