Reactive oxygen species in epoxidation reactions over titanosilicate molecular sieves

Shetti, Vasudev N.; Manikandan, P.; Srinivas, D.; Ratnasamy, P.

doi:10.1016/s0021-9517(02)00119-7

Cited by 69 publications

(62 citation statements)

References 19 publications

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“…The sharp absorption band near 330 nm and the broad background absorption band in the region 400-700 nm could be observed upon the fresh and recovered samples, the two bands correspond to the charge transfer of the absorbed PdO X and metallic Pd species, respectively, suggesting that part of the Pd is in the +2 oxidation state and the remaining in the zerooxidation state in the samples, the formation of Pd 2+ species on the fresh sample is likely to a prolonged exposure of Pd 0 species to air. Similar observations were made by Shetti et al [20] in the DRUV-visible spectra of Pd-TS-1 samples. It is noteworthy that two new bands near 300 and 394 nm, attributable to the V 5+ and V 4+ species, respectively [21], can also be observed upon the recovered sample, indicating that the adsorption of VO 3 -ions inside the pores of Pd/c-Al 2 O 3 has occurred during the reaction.…”

Section: Catalytic Testingsupporting

confidence: 89%

“…Based on the described above results, a synergistic catalytic mechanism, similar to one reported by Shetti et al [20], is proposed for the coupled reaction, as depicted in Scheme 2. Namely, the activated hydrogen molecule on the Pd 0 species easily reacts with AQ to form HAQ and the reduction of the V 5+ species to the V 4+ one is simultaneously achieved during the hydrogenation stage.…”

Section: Discussionsupporting

confidence: 59%

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A Promising Coupled Process of Pd/γ-Al2O3–NH4VO3 Catalyzing the Hydroxylation of Benzene with Hydrogen Peroxide Produced In Situ by an Anthraquinone Redox Route

Guo-sheng

Zhong

et al. 2007

Catal Lett

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A coupled process, of which Pd/c-Al 2 O 3 -NH 4 VO 3 catalyzed the hydroxylation of benzene with hydrogen peroxide produced in situ by an anthraquinone (AQ) redox route, was carried out via a sealed gaseous inner-circulated device under the atmospheric pressure. By means of such process, 0.57% of benzene conversion, 100% of phenol selectivity and 26.6% of anthraquinoneutilized efficiency were achieved upon the mixed Pd/cAl 2 O 3 -NH 4 VO 3 (V/Pd molar ratio for 4) in the presence of benzene/acetic acid (4v/10v). Above all, after the coupled reaction system was recycled three times, the accumulated phenol amount could achieve ca. 0.833 mmol and its average value (ca. 0.278 mmol) was slightly higher than phenol amount obtained in the first run (ca. 0.255 mmol), indicating that such coupled reaction system could be recycled efficiently. In addition, a synergistic mechanism was proposed to explain the favorable effect of V compound on the Pd/c-Al 2 O 3 catalyst.

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Section: Catalytic Testingsupporting

confidence: 89%

Section: Discussionsupporting

confidence: 59%

A Promising Coupled Process of Pd/γ-Al2O3–NH4VO3 Catalyzing the Hydroxylation of Benzene with Hydrogen Peroxide Produced In Situ by an Anthraquinone Redox Route

Guo-sheng

Zhong

et al. 2007

Catal Lett

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“…However, the reprocess procedure also affects the coordination of Ti by avoiding the formation of extra-framework Ti, thereby ensuring that essentially all the Ti 4+ ions in NHTS have a tetrahedral coordination (intra-framework). A single broad absorption band centered at around 485 nm, assigned to the absorption of noble metal species, [39] also appears in theUV/Vis spectra of NHTS and Pd/TS-1 (Figures 3, A and C), thus confirming the incorporation of noble metal species into NHTS and Pd/TS-1 and therefore the above XRD analysis. …”

Section: Uv/vis Diffuse Reflectance Spectra (Uv/vis)supporting

confidence: 68%

NHTS: A Hollow, Noble‐Metal‐Modified Titanium Silicalite

et al. 2009

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The major drawback of direct oxidation technology (onsite hydrogen peroxide production followed by its conversion into organic oxides without refining) is the design and preparation of the bifunctional catalysts used therein. Herein we present a bifunctional catalytic material (NHTS), which is synthesized by a revised semi-in-situ method that allows a noble metal to be distributed throughout the titanosilicate framework and also results in a redistribution of active Ti species throughout the crystals, thereby enriching the sur-

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“…In the literature these bands are ascribed to either (hydrated) Ti-hydroperoxide 65,66,70 or Ti-superoxide species. 71 In the UV-Vis DR spectrum of the spent Ti-G40-SBA catalyst in Fig. 8IV, four Gaussian functions were fitted.…”

Section: Role Of the Catalyst Materialsmentioning

confidence: 99%

Mechanistic insights in the olefin epoxidation with cyclohexyl hydroperoxide

Hereijgers

Parton

Weckhuysen

2012

Catal. Sci. Technol.

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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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Reactive oxygen species in epoxidation reactions over titanosilicate molecular sieves

Cited by 69 publications

References 19 publications

A Promising Coupled Process of Pd/γ-Al2O3–NH4VO3 Catalyzing the Hydroxylation of Benzene with Hydrogen Peroxide Produced In Situ by an Anthraquinone Redox Route

A Promising Coupled Process of Pd/γ-Al2O3–NH4VO3 Catalyzing the Hydroxylation of Benzene with Hydrogen Peroxide Produced In Situ by an Anthraquinone Redox Route

NHTS: A Hollow, Noble‐Metal‐Modified Titanium Silicalite

Mechanistic insights in the olefin epoxidation with cyclohexyl hydroperoxide

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