Active Sites and Reactive Intermediates in Titanium Silicate Molecular Sieves

Ratnasamy, P.; Srinivas, D.; Knözinger, H.

doi:10.1016/s0360-0564(04)48001-8

Cited by 365 publications

(260 citation statements)

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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%

“…[3,4] The synthesis of the microporous TS-1 zeolite was first patented by ENI using tetrapropylammonium (TPA), as a template agent. [5] The scientific and technological importance of TS-1 have already been discussed in our previous publication related to microand mesoporous titanosilicates where a number of physical analyses devoted to the bulk characterization of these materials have been compared to their surface analyses using XPS/X-rayexcited Auger electron spectroscopy (XAES).…”

Section: Introductionmentioning

confidence: 99%

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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%

Section: Introductionmentioning

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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“…[1][2] Generally, the active sites of TS-1 zeolite are produced by addition of hydrogen peroxide (H 2 O 2 ). Recently, Corma et al [3][4] found that TS-1 zeolite itself can catalyze chemical reactions because the Ti IV sites have vacant d orbitals and show Lewis acidity toward adsorbates.…”

Section: Introductionmentioning

confidence: 99%

Density Functional Calculations on the Distribution, Acidity, and Catalysis of Ti^IV and Ti^III Ions in MCM‐22 Zeolite

Yang

Zhou

Liu

et al. 2011

Chemistry A European J

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Isolated Ti species in zeolites show unique catalytic activities for a variety of chemical reactions. In this work, density functional calculations were used to explore three current concerns: 1) the distributions of TiIV and TiIII ions in the MCM‐22 zeolite; 2) the Lewis acidity of the TiIV and TiIII sites; and 3) activation of alkane CH bonds by photocatalysis with Ti‐doped zeolites. Neither the TiIV nor TiIII ions are randomly distributed in the MCM‐22 zeolite. The orders of relative stability are very close for the eight TiIV and TiIII sites, and the T3 site is the most probable in both cases. The wavelengths for TiIV–TiIII excitations were calculated to lie in the range λ=246.9–290.2 nm. The Ti3IV site shows Lewis acidity toward NH3 in two different modes, and these two modes can coexist with each other. The calculated TiIV coordination numbers, TiIVO bond elongations, and charge transfers caused by NH3 adsorption are in good agreement with previous results. Similarly, two different NH3 adsorption modes exist for the Ti3III site; the site that exhibits radical transfer from the lattice O to N atoms is preferred due to the higher adsorption energy. This indicates that the Ti3III site does not show Lewis acidity, in contrast to the Ti3IV site. At the Ti3III site, the energy barrier for activating the methane CH bond was calculated to be 33.3 kJ mol−1 and is greatly reduced by replacing the hydrogen atoms with methyl groups. In addition, the reactivity is improved when switching from MCM‐22 to TS‐1 zeolite. The studies on the various Ti species reveal that lattice O atoms rather than TiIII radicals are crucial to the activation of alkane CH bonds. This work provides new insights into and aids understanding of the catalysis by isolated Ti species in zeolites.

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“…11 Here, the best Ti : Si ratio of 3 : 100 corresponds well with previously reported maximum contents of Ti in TS-1 zeolite framework positions. 12 Catalytic oxidation with O 2 and H 2 on Au/TiO 2 -SiO 2 likely occurs by in situ formation of H 2 O 2 on Au. The H 2 O 2 then transfers to Ti tetrahedral sites to form Ti-OOH species active for selective oxidations, such as propylene epoxidation.…”

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confidence: 99%

“…1 and ESIw): (1) a band at about 540 nm due to a plasmon resonance (PR) of Au nanoparticles 15 (Au is mostly metallic as evidenced by the absence in the Au L 3 -edge XANES of a near-edge resonance around 11 920 eV due to oxidized Au, see ESIw); (2) band growth at 320-410 nm and 210-240 nm due to Ti-hydroperoxo species; 12,16 and (3) a band decrease at 250-300 nm due to tripodal Ti sites, Ti(OSi) 3 -OHÁ(H 2 O) 2 . 12 These assignments are supported by density functional theory (DFT) calculations (see ESIw). The Au PR position as a function of reaction time (Fig.…”

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confidence: 99%

Propane reacts with O2 and H2 on gold supported TS-1 to form oxygenates with high selectivity

et al. 2008

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Active Sites and Reactive Intermediates in Titanium Silicate Molecular Sieves

Cited by 365 publications

References 284 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

Density Functional Calculations on the Distribution, Acidity, and Catalysis of Ti^IV and Ti^III Ions in MCM‐22 Zeolite

Propane reacts with O2 and H2 on gold supported TS-1 to form oxygenates with high selectivity

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Active Sites and Reactive Intermediates in Titanium Silicate Molecular Sieves

Cited by 365 publications

References 284 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

Density Functional Calculations on the Distribution, Acidity, and Catalysis of TiIV and TiIII Ions in MCM‐22 Zeolite

Propane reacts with O2 and H2 on gold supported TS-1 to form oxygenates with high selectivity

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Density Functional Calculations on the Distribution, Acidity, and Catalysis of Ti^IV and Ti^III Ions in MCM‐22 Zeolite