Preference towards Five‐Coordination in Ti Silicalite‐1 upon Molecular Adsorption

Gallo, Erik; Bonino, Francesca; Swarbrick, Janine C.; Petrenko, Taras; Piovano, Andrea; Bordiga, Silvia; Gianolio, Diego; Groppo, Elena; Neese, Frank; Lamberti, Carlo; Glatzel, Pieter

doi:10.1002/cphc.201200893

Cited by 55 publications

(99 citation statements)

References 59 publications

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“…The TS-1 sample prepared by ENI (Instituto G. Donegani, Novara, Italy) and sodium form of ETS-10 prepared by Engelhard (Iselin, NJ, USA) were fully characterized elsewhere [34,35,48,49]. In the case of TS-1 the Ti loading was 2.98 wt%, as determined by the cell volume expansion, and the absence of extra phases of TiO 2 was carefully checked.…”

Section: Sample Preparationmentioning

confidence: 99%

Rational Design of Engineered Multifunctional Heterogeneous Catalysts. The Role of Advanced EPR Techniques

et al. 2015

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The importance of surface paramagnetic species owes much to that of surface phenomena which are involved in numerous areas of chemistry and material science such as heterogeneous catalysis, photochemistry and, in general terms, nano-sciences and technology. In the present contribution the opportunities offered by the use of EPR in the field of heterogeneous catalysis, with emphasis on the application of hyperfine techniques, will be illustrated taking as an example Ti-based catalytic materials. The reductive activation of framework titanium ions in the different materials and their sub-sequent reactivity towards NH 3 is followed, highlighting subtle differences in chemical reactivity related to the different matrixes.

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Section: Sample Preparationmentioning

confidence: 99%

Rational Design of Engineered Multifunctional Heterogeneous Catalysts. The Role of Advanced EPR Techniques

et al. 2015

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“…The background of the vtc-XES spectra, due to the Kβ 1,3 peak tail, was subtracted according to the procedure discussed in Ref. 35,36 . DFT calculations were performed within the one electron approximation using the 65 ORCA 2008 code.…”

Section: Techniquesmentioning

confidence: 99%

“…They can be used for ligand identification. 35,36,[44][45][46][48][49][50] Two Kβ" lines are present in the vtc-XES spectrum of Ti IV precursor (A and B in Figure 2c). According to previous works on Ti compounds, 35,44 A and B are 20 related to transitions involving MOs having primarily O(2s) and Cl(2p) character, respectively; hence, they identify the presence of oxygen and chlorine ligands in the first coordination sphere of the Ti sites.…”

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Silica-supported Ti chloride tetrahydrofuranates, precursors of Ziegler–Natta catalysts

et al. 2013

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The structural and electronic properties of silica-supported titanium chloride tetrahydrofuranates samples, obtained by impregnating a polymer-grade dehydroxylated silica with TiCl 4 (thf) 2 and TiCl 3 (thf) 3 complexes, precursors of Ziegler-Natta catalysts, are investigated by means of FT-IR, XAS, XES and diffuse reflectance UV-Vis spectroscopy, coupled with DFT calculations. The properties of the two silicasupported samples are very similar, irrespective of the starting precursor. In both cases, most of the 10 chlorine ligands originally surrounding the Ti sites are substituted by oxygen ligands upon grafting on silica. As a consequence, the electronic properties of silica-supported Ti sites are largely different from those of the corresponding precursors, and in both cases most of the grafted Ti sites have a formal oxidation state of +4. The whole set of experimental data provide evidence that mono-nuclear Ti species are mainly present at the silica surface.

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“…In principle, transitions involving Cl(3s) molecular orbitals could contribute in this energy region (as indicated by the label for the TiMg pre-catalyst), provided that they also have a Ti p contribution. [35,36,45] Also C ligands having sp 3 hybridization can contribute in the same energy region. As an example, the vtc-XES spectrum of TiC ( Figure S6) shows a prominent band at 4954 eV, which identifies the sp 3 hybridized carbon ligands.…”

Section: Introductionmentioning

confidence: 99%

XAS and XES Techniques Shed Light on the Dark Side of Ziegler–Natta Catalysts: Active‐Site Generation

et al. 2015

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The local structure and the electronic properties of the active Ti sites in heterogeneous Ziegler–Natta catalysts, generated in situ by interaction of the precatalyst with different Al‐alkyl activators, were investigated by combining X‐ray absorption and valence‐to‐core X‐ray emission spectroscopy (XAS and vtc‐XES), coupled with UV/Vis, FTIR, and DFT theoretical calculations. Irrespective of the activator used, the active system was found to be a highly dispersed TiCl3‐like phase in which the Ti sites are surrounded, not only by bridged chlorine ligands (with the same bond length of bulk TiCl3), but also by terminal chlorine ligands, at a much shorter distance. These results set Ziegler–Natta catalysts in the category of complex nanomaterials. Despite the observation that the investigated catalysts polymerize ethylene, cutting‐edge XAS and XES techniques do not yet offer unequivocal proof for the presence of any alkyl chain attached to the Ti sites, as a consequence of the small fraction of the active sites.

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Preference towards Five‐Coordination in Ti Silicalite‐1 upon Molecular Adsorption

Cited by 55 publications

References 59 publications

Rational Design of Engineered Multifunctional Heterogeneous Catalysts. The Role of Advanced EPR Techniques

Rational Design of Engineered Multifunctional Heterogeneous Catalysts. The Role of Advanced EPR Techniques

Silica-supported Ti chloride tetrahydrofuranates, precursors of Ziegler–Natta catalysts

XAS and XES Techniques Shed Light on the Dark Side of Ziegler–Natta Catalysts: Active‐Site Generation

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