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Olefin epoxidation with cyclohexyl hydroperoxide offers great perspective in increasing the yield from industrial cyclohexane oxidation and the production of epoxides in an apolar medium. Two competing hydroperoxide conversion routes, namely direct epoxidation and thermal decomposition, were identified. The formation of radicals seemed to play a role in both mechanisms. However, olefin epoxidation was found to solely take place at the catalyst. Allylic oxidation of cyclohexene occurs under reaction conditions primarily by molecular oxygen and only constitutes a minor route. The presence of molecular oxygen was found to increase the overall yield of the process by solvent oxidation yielding new cyclohexyl hydroperoxide. Hydrolysis and isomerization of the epoxide were found to be negligible reactions, although the epoxide gets converted at higher concentrations, presumably by the radical initiated polymerization. UV-Vis spectroscopy provided proof for the formation of titanium-hydroperoxide species as the active catalytic site in the direct epoxidation reaction.

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“…[22][23][24][25] In this regard, the use of an apolar reaction medium can offer the benefit of a prolonged catalyst lifetime.…”

Section: Introductionmentioning

confidence: 99%

Mechanistic insights in the olefin epoxidation with cyclohexyl hydroperoxide

Hereijgers

Parton

Weckhuysen

2012

Catal. Sci. Technol.

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“…[22,23] It is of great interest to develop novel porous titanosilicates with highly catalytic and stable Ti species that also have well-defined macroscopic morphologies, which can facilitate separation from reaction solutions.…”

Section: Introductionmentioning

confidence: 99%

Titanosilicate Beads with Hierarchical Porosity: Synthesis and Application as Epoxidation Catalysts

Lin

Lebedev

Tendeloo

et al. 2010

Chemistry A European J

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Porous titanosilicate beads with a diameter of 0.5-1.5 mm (TiSil-HPB-60) were synthesized from a preformed titanosilicate solution with a porous anion-exchange resin as template. The bead format of this material enables its straightforward separation from the reaction mixture in its application as a liquid-phase heterogeneous catalyst. The material displays hierarchical porosity (micro/mesopores) and incipient TS-1 structure building units. The titanium species are predominantly located in tetrahedral framework positions. TiSil-HPB-60 is a highly active catalyst for the epoxidation of cyclohexene with t-butyl hydroperoxide (TBHP) and aqueous H(2)O(2). With both oxidants, TiSil-HPB-60 gave higher epoxide yields than Ti-MCM-41 and TS-1. The improved catalytic performance of TiSil-HPB-60 is mainly ascribed to the large mesopores favoring the diffusion of reagents and products to and from the titanium active sites. The epoxide yield and selectivity could be further improved by silylation of the titanosilicate beads. Importantly, TiSil-HPB-60 is a stable catalyst immune to titanium leaching, and can be easily recovered and reused in successive catalytic cycles without significant loss of activity. Moreover, TiSil-HPB-60 is active and selective in the epoxidation of a wide range of bulky alkenes.

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“…The AA spectroscopy analysis showed that the titanium and vanadium loadings were slightly less than would be expected from the synthesis gel stoichiometry (see table 2); however, this trend in metal loading is common for doped silicate materials prepared by sol-gel techniques [19,34]. Carbon analysis results (not shown) for representative calcined samples indicated that only trace levels of carbon were present, which indicates that the bulk of the dendrimer template and organic solvents were removed by calcination.…”

Section: Elemental Analysismentioning

confidence: 94%

“…In recent years, several heterogeneous and homogeneous catalysts have been shown to be effective in the selective oxidation of alkenes [7][8][9][10][11]. Of the heterogeneous catalysts studied, mesoporous oxide materials have in many cases proven to be ideal because of their high surface areas, large pore diameters, mechanical strength, and controllable surface properties [12][13].…”

Section: Introductionmentioning

confidence: 99%

“…These materials, such as MCM-41, are prepared via sol-gel methods using surfactant structure-directing agents [14]. The catalytically active forms of these mesoporous oxides are readily synthesized via the impregnation of transition metals to yield metal-supported catalysts with high metal dispersions [15][16][17][18][19][20][21]. For example, researchers have shown that MCM-41 can be impregnated with small amounts of Ti ($2 wt%) to produce an effective catalyst for the selective oxidation of alkenes under mild conditions [20][21][22].…”

Section: Introductionmentioning

confidence: 99%

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Synthesis and Characterization of Dendrimer-Templated Mesoporous Oxidation Catalysts

2004

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We report here the use of 4th and 5th generation dendrimers poly(propylene)imine (CU-D32 and CU-D64) as templating agents for the synthesis of mesoporous titanosilicate and vanadosilicate oxidation catalysts via sol-gel techniques. The physical properties of these mesoporous materials were characterized by TGA, BET, PXD and SEM/EDX analyses and these showed that the transition metals are evenly distributed throughout these silicates, which have interconnected spherical pores (approx. 12 Å in diameter) and high surface areas of about 650 m 2 g À1 . Kinetic studies showed that all transition metal-doped catalysts were highly selective at oxidizing cyclohexene to the corresponding epoxide. Additionally, CU-D64-templated catalysts were more catalytically active for cyclohexene epoxidation than CU-D32-templated catalysts as a result of differences in pore size. All CU-D64-templated catalysts exhibited epoxidation catalytic activity comparable to that of titanium doped MCM-41 materials.

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Cited by 121 publications

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Mechanistic insights in the olefin epoxidation with cyclohexyl hydroperoxide

Mechanistic insights in the olefin epoxidation with cyclohexyl hydroperoxide

Titanosilicate Beads with Hierarchical Porosity: Synthesis and Application as Epoxidation Catalysts

Synthesis and Characterization of Dendrimer-Templated Mesoporous Oxidation Catalysts

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