Characterization of two different framework titanium sites and quantification of extra-framework species in TS-1 silicalites

Noc, L. Le; On, D. Trong; Solomykina, S.; Echchahed, Bousselham; Béland, François; Moulin, Christophe; Bonneviot, Laurent

doi:10.1016/s0167-2991(96)80272-2

Cited by 84 publications

(51 citation statements)

References 21 publications

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“…Since Ti 2p 3/2 peaks centered at ca. 460 eV and 458-459 eV have been assigned to a framework tetrahedral titanium and an extraframework octahedral titanium phase for titanosilicates, respectively [53,55,56], the present result is consistent with the formation of tetrahedral titanium species on the surface of 1a@SiMe 2 (H)-silica-cal.…”

Section: Characterization Of the Oxide Catalysts Prepared Using Ti-posssupporting

confidence: 88%

Ti-bridged silsesquioxanes as precursors of silica-supported titanium oxide catalysts for the epoxidation of cyclooctene

Sakugawa

Wada

Inoue

2010

Journal of Catalysis

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ABSTRACT:Silica-supported titanium oxide catalysts were prepared by the controlled calcination of Ti-bridged polyhedral oligomeric silsesquioxanes (POSS) bearing four Si-O-Ti bonds, Ti[(c-C 5 H 9 ) 7 Si 7 O 11 (OSiMe 2 R)] 2 (1a; R = vinyl, 1b; R = methyl) and Ti[(c-C 5 H 9 ) 8 Si 8 O 13 )] 2 (2), supported on various silicas, and these catalysts showed excellent activities for the epoxidation of cyclooctene by t BuOOH as an oxidant to selectively give cyclooctene oxide in high yields. On the other hand, catalysts prepared using a corner-capped-type Ti-containing POSS, CpTi[(c-C 5 H 9 ) 7 Si 7 O 12 ] (3, Cp = cyclopentadienyl), or tetraisopropoxytitanium (4) showed lower activities. The 2 catalysts prepared from Ti-bridged POSS can be easily separated from the reaction mixture and reused without a significant loss of activity. These catalysts were also applicable for the epoxidation of limonene. A spectroscopic study revealed that calcination of Ti-bridged POSS supported on silica gave isolated tetrahedral Ti(IV) species, which would be responsible for the high activity, while calcination of silicasupported 3 or 4 gave aggregated surface titanium oxide species.

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Section: Characterization Of the Oxide Catalysts Prepared Using Ti-posssupporting

confidence: 88%

Ti-bridged silsesquioxanes as precursors of silica-supported titanium oxide catalysts for the epoxidation of cyclooctene

Sakugawa

Wada

Inoue

2010

Journal of Catalysis

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“…This latter band can be assigned to isolated tetrahedral Ti(IV) LMCT 50 transitions. 16 It is also noteworthy that this absorption is shifted to a higher wavelength and becomes significantly broader in the monometallic Ti IV AlPO-5 catalyst (Fig. 4B, curve b), when compared with the bimetallic Co III Ti IV AlPO-5 (Fig.…”

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confidence: 85%

Engineering active sites for enhancing synergy in heterogeneous catalytic oxidations

et al. 2011

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“…230 nm (A 230 ). Such absorption peaks have also been observed in dehydrated TS-1 and attributed to two different framework sites as [Ti(OH)(OSi) 3 ] and [Ti(OSi) 4 ], 16 though their assignment to two peaks has not been fixed yet. Moreover, as has been reported by Marchese et al, there were two kinds of tetrahedral titanium sites in Ti-MCM-41 that were detected by photoluminescence measurements.…”

Section: Role Of Alkylsilyl Groups In Selective Production Of Epoxidementioning

confidence: 95%

“…It is clear from this figure that modification results in no appreciable broadening and/or shift of the spectrum to a longer wavelength range, indicating that the coordination number of titanium species was not affected by the modification, i.e., aggregation between isolated titanium species (T tet ) was not induced, and T tet /(T tet +T oct ) might therefore not be changed by the modification. 14 and [Ti(OSi) 4 ], 15 though their assignment to two peaks has not been fixed yet.…”

Section: Role Of Alkylsilyl Groups In Selective Production Of Epoxidementioning

confidence: 99%

Elucidation of the local structure of active titanium(iv) sites on silica-based phase-boundary catalysts for alkene epoxidation with aqueous hydrogen peroxide

Ikeue

Ikeda

Watanabe

et al. 2004

Phys. Chem. Chem. Phys.

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Structural and functional aspects of active titanium sites for phase boundary catalytic (PBC) epoxidation of 1-octene with hydrogen peroxide (H2O2) were investigated in detail using X-ray absorption fine structure (XAFS) analysis and ultraviolet and visible-light diffuse reflectance (UV-Vis-DR) spectroscopy. By analysis of the Ti K-edge X-ray absorption near edge fine structure (XANES) spectra of several titanium-loaded silica catalysts, the ratio of the amount of 4-coordinated titanium oxide (Ttet) to that of a 6-coordinated one (Toct) was determined. Monotonic increments of catalytic activity for epoxide production and efficiency of H2O2 utilization with the ratio Ttet/(Ttet + Toct) revealed that the highly active catalysts mainly include Ttet but not Toct. UV-Vis-DR spectra of samples with external surfaces partially covered with alkylsilyl groups indicated that there are at least two kinds of Ttet sites with different ligands. One site anchors an acidic hydroxyl (Ttet(OH)), giving absorption centered at the wavelength of ca. 230 nm and the other, exhibiting an absorption peak at the wavelength of ca. 210 nm, is directly attached to an alkylsilyl group (Ttet(OSiR)) formed via reaction of an acidic hydroxy of Ttet(OH) with an alkylsilane reagent. Since the catalysts have both an alkylsilyl-grafted hydrophobic surface and a hydroxy-terminated hydrophilic surface, it is postulated that the former is located on both hydrophilic (Ttet(OH,w)) and hydrophobic (Ttet(OH,o)) surfaces and the latter, Ttet(OSiR), exists only on the hydrophobic surface. From analyses of catalytic activities of several catalysts with different distributions of these Ttet sites, both Ttet(OH,o) and Ttet(OSiR) sites on the hydrophobic surface were proved to be active, while Ttet(OH,w) on the hydrophilic surface did not work for the present PBC system. Among the sites on the hydrophobic surface, moreover, it was found that a Ttet(OSiR) site acted as a more effective site for selective epoxidation when compared with Ttet(OH,o), which induced ring-opening of epoxide to give a by-product, 1,2-octanediol

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Characterization of two different framework titanium sites and quantification of extra-framework species in TS-1 silicalites

Cited by 84 publications

References 21 publications

Ti-bridged silsesquioxanes as precursors of silica-supported titanium oxide catalysts for the epoxidation of cyclooctene

Ti-bridged silsesquioxanes as precursors of silica-supported titanium oxide catalysts for the epoxidation of cyclooctene

Engineering active sites for enhancing synergy in heterogeneous catalytic oxidations

Elucidation of the local structure of active titanium(iv) sites on silica-based phase-boundary catalysts for alkene epoxidation with aqueous hydrogen peroxide

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