NMR Signatures and Electronic Structures of Ti-sites in Titanosilicalite-1 from solid-state 47/49Ti NMR Spectroscopy

Lätsch, Lukas; Müller, Imke; Hassan, Alia; Perrone, Barbara; Aghazada, Sadig; Berkson, Zachariah J.; Yakimov, Alexander V.; Baerdemaeker, Trees De; Parvulescu, Andrei‐Nicolae; Seidel, Karsten; Teles, J. Henrique; Copéret, Christophe

doi:10.26434/chemrxiv-2022-f71c2

Cited by 9 publications

(12 citation statements)

References 26 publications

(31 reference statements)

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“…V benefits from being a quadrupolar nucleus (I = 7/2) with a relatively small quadrupole moment compared to Ti ( 51 V = −0.043 b vs 47 Ti = 0.30 b and 49 Ti = 0.24 b) 27 and having a large chemical shift range (∼2000 ppm), thus ennobling excellent sensitivity toward small changes in the environment of the nucleus without the need for complex excitation schemes. Such an approach is currently very challenging for 47/49 Ti, 28 especially at low metal content. 29−31 In this work, we decided to focus on VOCl 3 @MgCl 2 (thf) 1.5 because of the large set of experimental data for the corresponding Ti-systems, TiCl 4 @MgCl 2 (thf) 1.5 .…”

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confidence: 99%

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Geometry and Local Environment of Surface Sites in Vanadium-Based Ziegler–Natta Catalysts from ⁵¹V Solid-State NMR Spectroscopy

Sabisch,

Kakiuchi,

Docherty

et al. 2023

J. Am. Chem. Soc.

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Since its emergence over 50 years ago, the structure of surface sites in Ziegler−Natta catalysts, which are responsible for a major fraction of the world's supply of polyethylene (PE) and polypropylene (PP), has remained elusive. This is in part due to the complexity of these systems that involve multiple synthetic steps and components, namely, the MgCl 2 support, a transition-metal chloride, and several organic modifiers, known as donors, that are used prior and in some instances during the activation step with alkyl aluminum. Due to the favorable nuclear magnetic resonance (NMR) properties of V and its use in Ziegler−Natta catalysts, we utilize 51 V solid-state NMR spectroscopy to investigate the structure of VOCl 3 on MgCl 2 (thf) 1.5 . The resulting catalyst shows ethylene polymerization activity similar to that of its Ti analogues. Using carefully benchmarked density functional theory (DFT) calculations, the experimental 51 V NMR signature was analyzed to elucidate the structure of the surface sites. Using this approach, we demonstrate that the 51 V NMR signature contains information about the coordination environment, i.e., the type of ancillary ligand, and the morphology of the MgCl 2 support. Analysis of the NMR signature shows that the adsorption of VOCl 3 on MgCl 2 (thf) 1.5 generates a well-defined hexacoordinated Voxo species containing one alkoxy and four chloride ligands, whose local geometry results from the interaction with an amorphous MgCl 2 surface. This study illustrates how NMR spectroscopy, which is highly sensitive to the local environment of the investigated nuclei, here V, enables us to identify the exact coordination sphere and to address the effect of the support morphology on surface site structures.

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confidence: 99%

“…This information should clearly be considered when trying to elucidate the structure of the corresponding Ti-based catalysts. Following our recent work on Ti-NMR, 28 quadrupolar NMR seems to be privileged to enable distinguishing specific surface sites even for the more challenging Ti-based ZNCs. 51 ■ ASSOCIATED CONTENT * sı Supporting Information…”

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confidence: 99%

Geometry and Local Environment of Surface Sites in Vanadium-Based Ziegler–Natta Catalysts from ⁵¹V Solid-State NMR Spectroscopy

Sabisch,

Kakiuchi,

Docherty

et al. 2023

J. Am. Chem. Soc.

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“…We selected nine representative Ti IV complexes (Figure 2) to establish our library. [Ti(OTBOS) 4 ] 32 (1) was chosen as a model for tetrahedral sites in titanosilicalite-1 (TS-1) and its related analogue [Ti(OiPr)(OTBOS) 3 ] 33 (2) to study the effect of subtle changes in electronic structure. We also selected [Ti 2 O 2 (acac) 4 ] 34 (3) (acac = acetylacetonate) and (PPN) 2 [OTiP 3 O 9 (acac)] 3 5 (4) (PPN = bis-(triphenylphos-phine)iminium) as octahedral mono-and dinuclear Ti sites, having either bridging or terminal oxo ligands.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Tracking Coordination Environment and Reaction Intermediates in Homogeneous and Heterogeneous Epoxidation Catalysts via Ti L_2,3-Edge Near-Edge X-ray Absorption Fine Structures

Lätsch,

Guda,

Romankov

et al. 2024

J. Am. Chem. Soc.

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Ti-based molecules and materials are ubiquitous and play a major role in both homogeneous and heterogeneous catalytic processes. Understanding the electronic structures of their active sites (oxidation state, local symmetry, and ligand environment) is key to developing molecular-level structure–property relationships. In that context, X-ray absorption spectroscopy (XAS) offers a unique combination of elemental selectivity and sensitivity to local symmetry. Commonly, for early transition metals such as Ti, K-edge XAS is applied for in situ characterization and subsequent structural analysis with high sensitivity toward tetrahedral species. Ti L2,3-edge spectroscopy is in principle complementary and offers specific opportunities to interrogate the electronic structure of five-and six-coordinated species. It is, however, much more rarely implemented because the use of soft X-rays implies ultrahigh vacuum conditions. Furthermore, the interpretation of the data can be challenging. Here, we show how Ti L2,3-edge spectroscopy can help to obtain unique information about both homogeneous and heterogeneous epoxidation catalysts and develop a molecular-level relationship between spectroscopic signatures and electronic structures. Toward this goal, we first establish a spectral library of molecular Ti reference compounds, comprising various coordination environments with mono- and dimeric Ti species having O, N, and Cl ligands. We next implemented a computational methodology based on multiplet ligand field theory and maximally localized Wannier orbitals benchmarked on our library to understand Ti L2,3-edge spectroscopic signatures. We finally used this approach to track and predict the spectra of catalytically relevant intermediates, focusing on Ti-based olefin epoxidation catalysts.

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“…50 Furthermore, solid-state 47/49 Ti NMR spectroscopy can be utilized to differentiate the Ti location at specific T-site positions. 90 By employing direct detection 15 N MAS NMR, it is possible to conduct precise measurements on the pyridine-Ti adducts. This allows us to discern and quantify the quantity of framework Ti centers accurately.…”

Section: Spatial Distribution Of Ti Speciesmentioning

confidence: 99%

“…The characterization of Ti active sites can be classified into direct and indirect methods. 90 Direct characterization methods mainly encompass UV−vis spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, UV-Raman spectroscopy, X-ray absorption spectroscopy, and solidstate 47/49 Ti nuclear magnetic resonance spectroscopy. Indirect characterization relies on probe molecules to determine Ti active sites.…”

Section: Spatial Distribution Of Ti Speciesmentioning

confidence: 99%

Constructing Highly Efficient Ti Sites of TS-1 for Alkene Epoxidation

Zhao,

Deng,

Lin

et al. 2023

Ind. Eng. Chem. Res.

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With the development of green engineering in manufacturing processes, emerging eco-sustainable technologies in chemical engineering systems has engendered a mounting interest. As one of the eco-sustainable green systems, alkene epoxidation with TS-1 and H2O2 is flourishing. In this review, a comprehensive summary for state-of-the-art synthetic strategies of high-efficient Ti sites in TS-1 for alkene epoxidation are summarized in three aspects (i.e., direct regulation of Ti active sites, physical structure adjustment of TS-1 particles, and regulation of microenvironment surrounding Ti active sites). These strategies could improve alkene epoxidation by modifying intrinsic active sites, improving molecules diffusion, adsorption, and desorption, and enhancing stability of reaction intermediates. Moreover, epoxidation mechanisms of different strategies and corresponding characterizations are elaborated and summarized systemically. Finally, we analyzed the current limitations and future perspectives on construction and characterization of high-efficiency Ti sites. This review could inspire more innovative research to boost the development of eco-sustainable alkene epoxidation.

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NMR Signatures and Electronic Structures of Ti-sites in Titanosilicalite-1 from solid-state 47/49Ti NMR Spectroscopy

Cited by 9 publications

References 26 publications

Geometry and Local Environment of Surface Sites in Vanadium-Based Ziegler–Natta Catalysts from ⁵¹V Solid-State NMR Spectroscopy

Geometry and Local Environment of Surface Sites in Vanadium-Based Ziegler–Natta Catalysts from ⁵¹V Solid-State NMR Spectroscopy

Tracking Coordination Environment and Reaction Intermediates in Homogeneous and Heterogeneous Epoxidation Catalysts via Ti L_2,3-Edge Near-Edge X-ray Absorption Fine Structures

Constructing Highly Efficient Ti Sites of TS-1 for Alkene Epoxidation

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NMR Signatures and Electronic Structures of Ti-sites in Titanosilicalite-1 from solid-state 47/49Ti NMR Spectroscopy

Cited by 9 publications

References 26 publications

Geometry and Local Environment of Surface Sites in Vanadium-Based Ziegler–Natta Catalysts from 51V Solid-State NMR Spectroscopy

Geometry and Local Environment of Surface Sites in Vanadium-Based Ziegler–Natta Catalysts from 51V Solid-State NMR Spectroscopy

Tracking Coordination Environment and Reaction Intermediates in Homogeneous and Heterogeneous Epoxidation Catalysts via Ti L2,3-Edge Near-Edge X-ray Absorption Fine Structures

Constructing Highly Efficient Ti Sites of TS-1 for Alkene Epoxidation

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Product

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Geometry and Local Environment of Surface Sites in Vanadium-Based Ziegler–Natta Catalysts from ⁵¹V Solid-State NMR Spectroscopy

Geometry and Local Environment of Surface Sites in Vanadium-Based Ziegler–Natta Catalysts from ⁵¹V Solid-State NMR Spectroscopy

Tracking Coordination Environment and Reaction Intermediates in Homogeneous and Heterogeneous Epoxidation Catalysts via Ti L_2,3-Edge Near-Edge X-ray Absorption Fine Structures