Modelling the active sites of heterogeneous titanium epoxidation catalysts using titanium silasequioxanes: insight into specific factors that determine leaching in liquid-phase processes

Abbenhuis, Hendrikus C. L.; Krijnen, S Simon; Santen, Rutger A. van

doi:10.1039/a607935k

Cited by 140 publications

(93 citation statements)

References 13 publications

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“…This cp-titanium-silsesquioxane complex is an efficient and robust epoxidation catalyst (50 • C, hexane, substrate: Ti, approx. 100 : 1) for oct-1-ene, cyclohexene and norbornylene (Abbenhuis et al 1997). In the case of cyclohexene and norbornylene, conversions of 90 per cent and selectivities of greater than 95 per cent were obtained in 3 h. The stability of {[(c-C 6 H 11 ) 7 Si 7 O 12 ]Ti(h 5 -C 5 Ph 5 )} under the catalytic conditions employed led van Santen and co-workers to immobilize the complex in the mesoporous silica MCM-41 (with Si/Al ratios of 42, 125 and ∞; Krijnen et al 1999).…”

Section: (A) Half-sandwich Complexes Of Titanium(iv) Silsesquioxanesmentioning

confidence: 99%

Silsesquioxanes as molecular analogues of single-site heterogeneous catalysts

et al. 2012

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We discuss herein selected examples of metal complexes of polyhedral oligosilsesquioxanes (POSSs) as models of single-site heterogeneous surface catalysts. The utility of these compounds as such models is illustrated when employed as analogues of single-site titanium species supported on a silica surface. Deep insights into structure-functionality relationships can be gained. In particular, it was possible to probe the relationship between accessibility of the reactive centre and turnover frequencies in a manner that is impossible for a purely heterogeneous catalyst. We also report that the partially dehydroxylated SiO 2 surface alone is an effective radical polymerization initiation catalyst. This surface reactivity is modelled by the solution reactions between the olefin substrate and two POSSs, the completely condensed triganol prism, Si 6 Cy 6 O 9 (a6b0, Cy = Cyclohexyl, C 6 H 11 ), and the incompletely condensed partial cube, Si 7 Cy 7 O 9 (OH) 3 (a7b3). The former, with six-membered Si 3 O 3 rings, is a catalyst. The latter, without this feature, is not. Similar reactivity discrimination is observed in the gas phase reactions of these POSSs with the olefin substrate, examined using atmospheric pressure chemical ionization-and collision-induced decomposition spectroscopies. Silsesquioxane a6b0, containing Si 3 O 3 rings, reacts with the olefin, forming grafted olefin monomers and dimers, while this reactivity is not observed with silsesquioxane a7b3.

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Section: (A) Half-sandwich Complexes Of Titanium(iv) Silsesquioxanesmentioning

confidence: 99%

Silsesquioxanes as molecular analogues of single-site heterogeneous catalysts

et al. 2012

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“…DFT calculations are increasingly being applied to predict the interactions of adsorbates with catalytic sites [10]. Such DFT methods provided accurate geometries and reasonable energetics for molecules containing transition metals [11][12][13][14] are sufficient to describe the active sites in comparison of the predictions with experimental data.…”

Section: Introductionmentioning

confidence: 99%

DRIFTS investigation and DFT calculation of the adsorption of CO on Pt/TiO2, Pt/CeO2 and FeOx/Pt/CeO2

Gao

et al. 2008

Spectrochimica Acta Part A: Molecular and Biomolecular Spectros

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“…Other Ti-containing POSS, 1b and 2 (see Scheme 2), showed similar activities (entries 3 and 4). The activities of Ti-containing POSS as homogeneous catalysts for the epoxidation by organic peroxides have been previously reported [16][17][18][19][20][21][22][23]. Silica-tethered 1a showed a catalytic activity similar to that of 1a, indicating that 1a was tethered without a loss of activity (entry 5).…”

Section: Methodsmentioning

confidence: 84%

“…In particular, the catalytic activities of Ti-containing POSS for the epoxidation of alkenes have been examined [16][17][18][19][20][21][22][23]. In addition to their activities as homogeneous catalysts, their application to heterogeneous catalysis using metal-containing POSS as precursors has been examined [10,13,15,[24][25][26][27][28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

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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Modelling the active sites of heterogeneous titanium epoxidation catalysts using titanium silasequioxanes: insight into specific factors that determine leaching in liquid-phase processes

Cited by 140 publications

References 13 publications

Silsesquioxanes as molecular analogues of single-site heterogeneous catalysts

Silsesquioxanes as molecular analogues of single-site heterogeneous catalysts

DRIFTS investigation and DFT calculation of the adsorption of CO on Pt/TiO2, Pt/CeO2 and FeOx/Pt/CeO2

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

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