Oxidation of norbornene over vanadium-substituted phosphomolybdic acid catalysts and spectroscopic investigations

Raj, N.K. Kala; Ramaswamy, A.V.; Manikandan, P.

doi:10.1016/j.molcata.2004.10.005

Cited by 58 publications

(38 citation statements)

References 44 publications

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“…In order for Nb-(O 2 ) to undergo a 2eoxidation (e.g., olefin epoxidation), the process must involve concomitant oxidation of the Nb-metal center from Nb IV to Nb V and the reformation of a Nb-O-Si framework bond. Similar processes have been proposed to occur through a biradical, stepwise reaction on homogeneous vanadium complexes [75,76], and Nb-(O 2 )superoxide species may react in an analogous manner (Scheme S2). The epoxidation of cis-stilbene provides one method to test this hypothesis and to determine whether the epoxidation reaction proceeds through a concerted reaction or by a stepwise reaction, which would be consistent with the participation of Nb IV -(O 2 ) as the active intermediate Figure 7a shows that the rate of epoxidation depends inversely on the C 6 Therefore, the mechanism shown below (Scheme 3) differs from previous proposals in a few significant ways.…”

Section: Nbmentioning

confidence: 60%

Kinetic and spectroscopic evidence for reaction pathways and intermediates for olefin epoxidation on Nb in *BEA

Bregante

Priyadarshini

Flaherty

2017

Journal of Catalysis

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2Graphical Abstract -TOC 3 AbstractThe selective epoxidation of olefins with hydrogen peroxide (H 2 O 2 ) over transition metal substituted zeolites is less environmentally impactful than epoxidation schemes that use chlorinated or organic oxidants. The structure and reactivity of reactive intermediates derived from H 2 O 2 and the mechanism for olefin epoxidation on such materials are debated. Here, cyclohexene oxide formation and H 2 O 2 decomposition rates (measured as functions of reactant and product concentrations) and in situ infrared (IR) and UV-vis spectroscopy are used to probe the intervening elementary steps for cyclohexene (C 6 H 10 ) epoxidation and the identity of the reactive intermediates on a Nb-β catalyst. IR and UV-vis spectra acquired in situ show that the reactive intermediates are predominantly superoxide species (Nb IV -(O 2 ) -; observed also by X-ray photoelectron spectroscopy), which form by the irreversible activation of H 2 O 2 over Nb centers.Similar M-(O 2 )* (M= Ti or Ta) intermediates were previously assumed to form via reversible processes; however, in situ IR and UV-vis measurements directly show that Nb IV -(O 2 )forms irreversibly in both H 2 O and acetonitrile. Activation enthalpies (ΔH ‡ ) for C 6 H 10 epoxidation are 27 kJ mol -1 higher than for H 2 O 2 decomposition, while activation entropies (ΔS ‡ ) for epoxidation are 56 J mol -1 K -1 lower than for H 2 O 2 . These comparisons show that the selectivities for epoxidation, via primary reaction pathways, increase with increasing reaction temperatures.Collectively, these results provide a self-consistent mechanism for C 6 H 10 epoxidation that is also in agreement with previously published data. These findings will aid the rational design and study of alternative metal oxide catalysts for olefin oxidation reactions.

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Section: Nbmentioning

confidence: 60%

Kinetic and spectroscopic evidence for reaction pathways and intermediates for olefin epoxidation on Nb in *BEA

Bregante

Priyadarshini

Flaherty

2017

Journal of Catalysis

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“…The probable products during the oxidation of norbornene include 2,3-epoxynorborane, 2-norbornanone and exo, endo-norborneols. Oxidations of norbornene were carried out by a number of catalytic systems [23][24][25][26] but the selectivity and yield of epoxide are moderate in most of the cases [27]. The present oxidizing system selectively oxidizes norbornene to exo-epoxynorborane at room temperature.…”

Section: Resultsmentioning

confidence: 95%

Chiral Mn(III) salen catalyzed oxidation of hydrocarbons

Biswas

Das

Kandar

et al. 2010

Transition Met Chem

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Four chiral manganese(III)-salen complexes (1-4) were employed as catalysts in the oxidation of hydrocarbons at room temperature using pentafluoroiodosylbenzene as terminal oxidant. The reactions were carried out in acetonitrile and dichloromethane. Norbornene has been selectively oxidized to exo-epoxynorborane in 85% yield. At room temperature, oxygenation of cyclohexane up to 14% in acetonitrile medium has also been achieved.

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“…According to the results the reaction was selective to cyclohexene oxide (epoxide) and the conversion increases with the increase of the active phase. Monomeric, dimeric, and tetrameric peroxo species are generated by the reaction of polyoxometalates with hydrogen peroxide, and the peroxo species are supposed to be the active species for epoxidation of olefins within a POM/H 2 O 2 system [18][19][20]. Best yields and selectivity are reached with 40% PVMo/Hmont (conversion 98% and 89% of cyclohexene epoxide).…”

Section: Cyclohexene Oxidationmentioning

confidence: 99%

Oxidation of Cyclohexene with H₂O_{_2} Catalyzed by Vanadium Based Polyoxometalates Doped Modified Clays as Green Catalysts

2017

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The catalytic performance of supported heteropolyacids in various liquid-solid and gas-solid heterogeneous reactions may be affected by the choice of support and/or the method of heteropolyacid deposition. Vanadium substituted polyphosphomolybdate with the Keggin structure H4[PVMo11O40]·13H2O (PVMo) was dispersed throughout acid activated bentonite (clay from Hammam Boughrara, Maghnia, Algeria). A series of catalysts were prepared via modified impregnation. Modified preparation method employed ultrasonication as a means of the dispersion homogenization, followed by freeze-drying. The catalysts were characterized by the Brunauer-Emmett-Teller, the Fourier transform infrared, and 31 P solid-state magic angle spinning-NMR spectroscopy. The catalytic performance of PVMo/Hmont was evaluated in the oxidation of cyclohexene. Intact Keggin anions were preserved on Hmont after deposition aided by ultrasonication. The obtained results showed that a better catalytic activity can be obtained with PVMo/bentonite (98% of conversion and 89% of cyclohexene oxide), by drop addition of H2O2, for 3 h.

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Oxidation of norbornene over vanadium-substituted phosphomolybdic acid catalysts and spectroscopic investigations

Cited by 58 publications

References 44 publications

Kinetic and spectroscopic evidence for reaction pathways and intermediates for olefin epoxidation on Nb in *BEA

Kinetic and spectroscopic evidence for reaction pathways and intermediates for olefin epoxidation on Nb in *BEA

Chiral Mn(III) salen catalyzed oxidation of hydrocarbons

Oxidation of Cyclohexene with H₂O_{_2} Catalyzed by Vanadium Based Polyoxometalates Doped Modified Clays as Green Catalysts

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Oxidation of norbornene over vanadium-substituted phosphomolybdic acid catalysts and spectroscopic investigations

Cited by 58 publications

References 44 publications

Kinetic and spectroscopic evidence for reaction pathways and intermediates for olefin epoxidation on Nb in *BEA

Kinetic and spectroscopic evidence for reaction pathways and intermediates for olefin epoxidation on Nb in *BEA

Chiral Mn(III) salen catalyzed oxidation of hydrocarbons

Oxidation of Cyclohexene with H2O_2 Catalyzed by Vanadium Based Polyoxometalates Doped Modified Clays as Green Catalysts

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Oxidation of Cyclohexene with H₂O_{_2} Catalyzed by Vanadium Based Polyoxometalates Doped Modified Clays as Green Catalysts