Epoxidation on titanium-containing silicates: do structural features really affect the catalytic performance?

Ravasio, Nicoletta; Psaro, Rinaldo; Ferraris, Giovanni; Moretti, Giuliano

doi:10.1016/s0021-9517(02)00152-5

Cited by 104 publications

(37 citation statements)

References 22 publications

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“…3. In all spectra, the bands at about 3437 and 1636 cm −1 can be attributed to the stretching vibration of hydroxyl and water, respectively [26]. It has been reported that adsorbed water, which is probably due to humid KBr and incorporated humidity in the process of sample preparation, has two bands around 3400 and 1630 cm −1 [27,28], while Ti-OH bonding presents three bands around 3563, 3172 and 1600 cm −1 [29].…”

Section: Ft-irmentioning

confidence: 77%

Synthesis of nano titania particles embedded in mesoporous SBA-15: Characterization and photocatalytic activity

Yang¹,

Jun²,

Zhu³

et al. 2006

Journal of Hazardous Materials

188

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Section: Ft-irmentioning

confidence: 77%

Synthesis of nano titania particles embedded in mesoporous SBA-15: Characterization and photocatalytic activity

Yang¹,

Jun²,

Zhu³

et al. 2006

Journal of Hazardous Materials

188

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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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“…The main advantage of our process is that the renewable raw materials used for the preparation of the catalysts, with adequate design, can give rise to catalysts that can compete with synthetic ones, prepared usually in more expensive and time consuming ways and therefore less environmentally friendly [34].…”

Section: Sustainable Fine Chemicals From Agri Wastesmentioning

confidence: 99%

Sustainable Materials and Biorefinery Chemicals from Agriwastes

Martín-Luengo¹,

Yates²,

Ramos³

et al. 2012

Resource Management for Sustainable Agriculture

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Epoxidation on titanium-containing silicates: do structural features really affect the catalytic performance?

Cited by 104 publications

References 22 publications

Synthesis of nano titania particles embedded in mesoporous SBA-15: Characterization and photocatalytic activity

Synthesis of nano titania particles embedded in mesoporous SBA-15: Characterization and photocatalytic activity

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

Sustainable Materials and Biorefinery Chemicals from Agriwastes

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