Microporous Crystalline Titanium Silicates

Notari, Bruno

doi:10.1016/s0360-0564(08)60042-5

Cited by 741 publications

(501 citation statements)

References 171 publications

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“…The active site of TS-1 is modeled by a five-tetrahedral (5T) cluster (OH) 2 Ti[OSi(OH) 2 OSiH 3 ] 2 selected from the ZSM-5 zeolite structure where the Ti atom is located at the T12 site. To have a more accurate description of the active site, OH terminations were used for Si atoms closed to the Ti atom.…”

Section: Methodsmentioning

confidence: 99%

“…Ti-substituted silicalite (TS-1) has been widely used as a catalyst for several important oxidation reactions such as the olefin epoxidation, the phenol hydroxylation, cyclohexanone amoxidation, as well as the conversions of ammonia to hydroxylamine, of secondary alcohol to ketone, and of secondary amine to dialkylhydroxylamine [1][2][3][4][5][6][7]. In particular, its use in alkene epoxidation reactions with hydrogen peroxide as oxidant has been experimentally [4][5][6][7] and theoretically [8][9][10][11][12][13][14][15] studied.…”

Section: Introductionmentioning

confidence: 99%

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Density functional theory study of the ethylene epoxidation over Ti-substituted silicalite (TS-1)

Limtrakul

Inntam

Truong

2004

Journal of Molecular Catalysis A: Chemical

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The mechanism of ethylene epoxidation with hydrogen peroxide over Ti-substituted silicalite (TS-1) catalyst was investigated by using both the cluster and embedded cluster approaches at the B3LYP/6-31G(d) level of theory. The complete catalytic cycle was determined. The epoxidation of ethylene consists of three steps. First, the chemisorption of H 2 O 2 at the Ti active site forms the oxygen donating Ti-OOH species and then the transfer of an oxygen atom from the Ti-OOH species to the adsorbed ethylene. The final step is the dehydration of the Ti-OH species to regenerate to active center. The oxygen atom transfer step was found to be the rate-limiting step with the zero-point energy corrected barrier of 17.0 kcal/mol using the embedded cluster model at B3LYP/6-31G(d) level of theory, which is in agreement with the experimental estimate of about 16.7 kcal/mol. Regeneration of the active center by dehydration of the Ti-OOH species was found to have a rather small barrier and the overall process is exothermic. Our results also show that inclusion of the effects of the zeolite crystal framework is crucial for obtaining quantitative energetic information. For instance, the Madelung potential increases the barrier of the oxygen atom transfer step by 5.0 kcal/mol.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Density functional theory study of the ethylene epoxidation over Ti-substituted silicalite (TS-1)

Limtrakul

Inntam

Truong

2004

Journal of Molecular Catalysis A: Chemical

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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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“…Titanium-based microporous (e.g. titanosilicates such as TS-1) 8 and mesoporous solids (e.g. TiMCM-41) 9 have proved 30 particularly effective in epoxidation reactions.…”

mentioning

confidence: 99%

Engineering active sites for enhancing synergy in heterogeneous catalytic oxidations

et al. 2011

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Microporous Crystalline Titanium Silicates

Cited by 741 publications

References 171 publications

Density functional theory study of the ethylene epoxidation over Ti-substituted silicalite (TS-1)

Density functional theory study of the ethylene epoxidation over Ti-substituted silicalite (TS-1)

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

Engineering active sites for enhancing synergy in heterogeneous catalytic oxidations

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Microporous Crystalline Titanium Silicates

Cited by 741 publications

References 171 publications

Density functional theory study of the ethylene epoxidation over Ti-substituted silicalite (TS-1)

Density functional theory study of the ethylene epoxidation over Ti-substituted silicalite (TS-1)

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

Engineering active sites for enhancing synergy in heterogeneous catalytic oxidations

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Product

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