Modeling Coadsorption of Titanium Tetrachloride and Bidentate Electron Donors on Magnesium Dichloride Support Surfaces

Bazhenov, Andrey S.; Denifl, Peter; Leinonen, Timo; Pakkanen, Anneli; Linnolahti, Mikko; Pakkanen, Tapani A.

doi:10.1021/jp508693h

Cited by 34 publications

(33 citation statements)

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“… 18 Consensus has been reached about (104) surfaces, exposing pentacoordinated magnesium sites, as being thermodynamically more stable than (110) surfaces, exposing tetracoordinated magnesium sites. 7 , 8 , 15 , 19 The addition of donors to the surface can significantly change the picture to favor the (110) sites, especially for 1,3-diethers. 6 , 8 , 15 , 20 Traditionally, TiCl 4 was believed to form Ti 2 Cl 8 dimers on the (104) surface, 3 while donors would cover the more acidic and nonstereoselective (110) sites.…”

Section: Introductionmentioning

confidence: 99%

“… 7 , 8 , 15 , 19 The addition of donors to the surface can significantly change the picture to favor the (110) sites, especially for 1,3-diethers. 6 , 8 , 15 , 20 Traditionally, TiCl 4 was believed to form Ti 2 Cl 8 dimers on the (104) surface, 3 while donors would cover the more acidic and nonstereoselective (110) sites. However, recent computational and experimental results show a preferential binding of TiCl 4 monomers to the (110) surface.…”

Section: Introductionmentioning

confidence: 99%

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Structural Characterization of Electron Donors in Ziegler–Natta Catalysts

et al. 2018

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Ziegler–Natta catalysis is a very important industrial process for the production of polyolefins. However, the catalysts are not well-understood at the molecular level. Yet, atomic-scale structural information is of pivotal importance for rational catalyst development. We applied a solid-state NMR/density functional theory tandem approach to gain detailed insight into the interactions between the catalysts’ support, MgCl2, and organic electron donors. Because of the heterogeneity of the samples, large line widths are observed in the carbon spectra. Despite this, good agreement between experimental and computational values was reached, and this shows that 1,3-diether based donors coordinate at (110) surface sites, while phthalates are less selective and coordinate at both (104) and (110) surface sites.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Structural Characterization of Electron Donors in Ziegler–Natta Catalysts

et al. 2018

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“…However, coordination of electron donors can reverse the relative stabilities so that the (110)-surface sites become more stable than the (104)-surface. 5 , 7 , 14 , 17 , 18 Some computational studies go one step further and look at the role that the donors play in the whole catalytic cycle. 19 − 21 …”

Section: Introductionmentioning

confidence: 99%

Probing Interactions between Electron Donors and the Support in MgCl₂-Supported Ziegler–Natta Catalysts

Blaakmeer

Antinucci

Eck³

et al. 2018

J. Phys. Chem. C

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Olefin polymerization using Ziegler–Natta catalysts (ZNCs) is an important industrial process. Despite this, fundamental insight into the inner working mechanisms of these catalysts remains scarce. Here, we focus on the low-γ nuclei 25Mg and 35Cl for an in-depth solid-state NMR and density functional theory (DFT) study of the catalyst’s MgCl2 support in binary adducts prepared by ball-milling. Besides the bare MgCl2 support and a MgCl2–TiCl4 adduct, samples containing donors that are part of the families of 2,2-dialkyl-1,3-dimethoxypropanes and phthalates used in fourth- and fifth-generation ZNCs are studied. DFT calculations indicate that the quadrupolar coupling parameters of the chlorines differ significantly between bulk and surface sites. As a result, the NMR visibility of the chlorine sites correlates with the particle size except for the adduct with 2,2-dimethyl-1,3-dimethoxypropane donor. The DFT calculations furthermore show that the surface sites are fairly insensitive to binding of different donor molecules, making it difficult to identify specific binding motives. The surface sites with large 35Cl NMR line widths can be observed using high radio frequency field strengths. For the 2,2-dimethyl-1,3-dimethoxypropane donor, we observe additional surface sites with intermediately high quadrupolar couplings, suggesting a different surface structure for this particular adduct compared to the other systems. For 25Mg, pronounced effects of donor binding on the quadrupole interaction parameters are observed, both computationally and experimentally. Again the adduct with the 2,2-dimethyl-1,3-dimethoxypropane donor shows a different behavior of the surface sites compared to the other adducts, which display more asymmetric coordinations of the surface Mg sites. Identifying specific binding motives by comparing 25Mg NMR results to DFT calculations also proves to be difficult, however. This is attributed to the existence of many defect structures caused by the ball-milling process. The existence of such defect structures both at the surface and in the interior of the MgCl2 particles is corroborated by NMR relaxation studies. Finally, we performed heteronuclear correlation experiments, which reveal interactions between the support and Mg–OH surface groups, but do not provide indications for donor–surface interactions.

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“…7−10 Lateral cut of the MgCl 2 sheets exposes catalytically relevant (104) and (110) surfaces with five- and four-coordinate Mg atoms, respectively (Figure 1B), 11 which adsorb and coadsorb TiCl 4 , aluminum alkyls, and Lewis bases. 12−20 The (110) surface is less stable than the (104) surface because of the lower coordination numbers of surface Mg atoms, 18,19,21 but adsorption of other catalyst components may reverse the stability order in favor of (110). 22,23 Reactions taking place on the surface eventually lead to the formation of active sites for olefin polymerization.…”

Section: Introductionmentioning

confidence: 99%

Adsorption of Titanium Tetrachloride on Magnesium Dichloride Clusters

Zorve

Linnolahti

2018

ACS Omega

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Magnesium dichloride and titanium tetrachloride are key components in heterogeneous Ziegler–Natta olefin polymerization catalysis. We have determined the preferred binding modes of titanium tetrachloride on magnesium dichloride clusters at the M06-2X level of theory, thus accounting for dispersion. A systematic study was carried out to locate the lowest energy isomers of (MgCl 2 ) n (TiCl 4 ) m complexes. Altogether ca. 1000 complexes with n ranging from 1 to 19 and m from 1 to 13 were studied. In line with the previous literature, the results consistently show that adsorption of TiCl 4 onto MgCl 2 preferably leads to octahedral six-coordination for both Mg and Ti atoms. This can be achieved by mononuclear binding of TiCl 4 and binuclear binding of Ti 2 Cl 8 on (110) and (104) surfaces of MgCl 2 , respectively. The preferred octahedral six-coordination is also achieved by binding of TiCl 4 on defect sites, of which the most striking example is trinuclear binding mode at corners of the clusters. Overall, the results highlight the relevance of multinuclear binding of TiCl 4 on MgCl 2 .

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Modeling Coadsorption of Titanium Tetrachloride and Bidentate Electron Donors on Magnesium Dichloride Support Surfaces

Cited by 34 publications

References 49 publications

Structural Characterization of Electron Donors in Ziegler–Natta Catalysts

Structural Characterization of Electron Donors in Ziegler–Natta Catalysts

Probing Interactions between Electron Donors and the Support in MgCl₂-Supported Ziegler–Natta Catalysts

Adsorption of Titanium Tetrachloride on Magnesium Dichloride Clusters

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Modeling Coadsorption of Titanium Tetrachloride and Bidentate Electron Donors on Magnesium Dichloride Support Surfaces

Cited by 34 publications

References 49 publications

Structural Characterization of Electron Donors in Ziegler–Natta Catalysts

Structural Characterization of Electron Donors in Ziegler–Natta Catalysts

Probing Interactions between Electron Donors and the Support in MgCl2-Supported Ziegler–Natta Catalysts

Adsorption of Titanium Tetrachloride on Magnesium Dichloride Clusters

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Probing Interactions between Electron Donors and the Support in MgCl₂-Supported Ziegler–Natta Catalysts