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Saxton, Robert

doi:10.1023/a:1019102320274

Cited by 73 publications

(37 citation statements)

References 2 publications

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“…Both species can adapt their coordination in relation to the environmental conditions. It remains to establish to which of the two sites the TS-1 catalytic role can be attributed, considering that applicative studies have shown already the superior activity of Ti(IV) anchored species as catalysts [3,15] with the presence of Ti(III) also considered to be central for the redox activity.…”

Section: Discussionmentioning

confidence: 99%

XPS characterization of a synthetic Ti‐containing MFI zeolite framework: the titanosilicalites, TS‐1

Langerame

Salvi

Silletti

et al. 2008

Surface & Interface Analysis

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Following a previous investigation on micro-and mesoporous titanosilicates, we have here deepened the XPS and Xray-excited Auger electron spectroscopy (XAES) studies on the surface properties of microporous titanosilicalites-1 (TS-1) and reference silicalites-1 (S-1), both characterized by the MFI framework type. The aim was that of complementing the information already obtained on these compounds with other techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), dielectric relaxation spectroscopy (DRS), electron spin resonance (ESR), and quantomechanical calculations. Notwithstanding the expected low photoelectron intensity due to the very low solubility of Ti (IV) ions in the MFI framework, an accurate XPS curve-fitting procedure and the simultaneous use of the XPS and Auger signals (Wagner plot) have made possible, both qualitatively and quantitatively, the distinction of two Ti (IV) sites: the framework tetrahedral species -Ti (IV) substituting Si (IV) -and the Ti(IV) tetrahedral species grafted to surface hydroxyl groups. Both species are prone to convert into octahedrally coordinated Ti (IV) species as a consequence of interaction with water and other ligands.

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Section: Discussionmentioning

confidence: 99%

XPS characterization of a synthetic Ti‐containing MFI zeolite framework: the titanosilicalites, TS‐1

Langerame

Salvi

Silletti

et al. 2008

Surface & Interface Analysis

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“…Indeed, titanosilicates represent a class of materials broadly used in epoxidation but only understood at the atomic level in a limited way [3,[8][9][10][11][12][13], . For example, while there is agreement that six-coordinate, coordinatively saturated Ti sites, as found in bulk TiO 2 , are inactive, it remains unobvious whether the ideal site for catalysis is an isolated Ti or slightly oligomeric species with Ti-O-Ti connectivity [14].…”

Section: Introductionmentioning

confidence: 99%

Effect of Coordination Environment in Grafted Single-Site Ti-SiO2 Olefin Epoxidation Catalysis

et al. 2016

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The effect of calixarene ligand symmetry, as dictated by lower-rim substitution pattern, on the coordination to a Ti(IV) cation is assessed in solution and when grafted on SiO 2 , and its effect on epoxidation catalysis by Ti(IV)-calixarene grafted on SiO 2 is investigated. C 2v symmetric Ti-tert-butylcalix[4]arene complexes that are 1,3-alkyl disubstituted at the lower rim (di-R-Ti) are compared to previously reported grafted C s symmetric complexes, which are singly substituted at the lower rim (mono-R-Ti). 13 C MAS NMR spectra of complexes isotopically enriched at the lower-rim alkyl position indicate that di-R-Ti predominantly grafts onto silica as the conformation found in solution, exhibiting a deshielded alkyl resonance compared to the grafted mono-R-Ti complexes, which is consistent with stronger alkyl ether?Ti dative interactions that are hypothesized to result in higher electron density at the Ti center. Moreover, 13 C MAS NMR spectroscopy detects an additional contribution from an ''endo'' conformer for grafted di-R-Ti sites, which is not observed in solution. Based on prior molecular modeling studies and on 13 C MAS NMR spectroscopy chemical shifts, this ''endo'' conformer is proposed to have similar Ti-(alkyl ether) distances at the lower-rim and electron density at the Ti center relative to grafted mono-R-Ti complexes. Differences between grafted mono-R-Ti and di-R-Ti sites can be observed by ligand-to-metal charge transfer edge-energies, calculated from diffuse-reflectance UV-visible spectroscopy at 2.24 ± 0.02 and 2.16 ± 0.02 eV, respectively. However, rates of tert-butyl hydroperoxide consumption in the epoxidation of 1-octene are found to be largely unchanged when compared to those of the grafted mono-R-Ti complexes, with average rate constants of *1.5 M -2 s -1 and initial TOF of *4 ks -1 at 323 K. This suggests that an ''endo'' conformation of grafted di-R-Ti may prevail during catalysis. Despite this, grafted di-C 1 -Ti complexes can be more selective than mono-C 1 -Ti complexes (45 vs. 34 % at a 50 % conversion at 338 and 353 K), illustrating the importance of the Ti coordination environment on epoxidation catalysis.

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“…A titanium silicalite zeolite having a MFI structure (TS-1 or Ti-MFI) has shown excellent catalytic properties in a wide range of selective oxidation reactions [1,2]. The oxidant used in oxidation reactions with Ti-MFI is often aqueous hydrogen peroxide, which is a green oxidant because its final product is water.…”

Section: Introductionmentioning

confidence: 99%

Hydrophobicity and catalytic properties of Ti-MFI zeolites synthesized by microwave and conventional heating

Xu¹,

Jin²,

Jhung³

et al. 2006

Catalysis Today

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Untitled

Cited by 73 publications

References 2 publications

XPS characterization of a synthetic Ti‐containing MFI zeolite framework: the titanosilicalites, TS‐1

XPS characterization of a synthetic Ti‐containing MFI zeolite framework: the titanosilicalites, TS‐1

Effect of Coordination Environment in Grafted Single-Site Ti-SiO2 Olefin Epoxidation Catalysis

Hydrophobicity and catalytic properties of Ti-MFI zeolites synthesized by microwave and conventional heating

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