Toward Understanding the Unusual Reactivity of Nb-Containing Catalysts in Epoxidation of C=C Bonds with Hydrogen Peroxide Full article
| Journal |
Journal of Catalysis
ISSN: 0021-9517 , E-ISSN: 1090-2694 |
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| Output data | Year: 2017, Volume: 356, Pages: 85-99 Pages count : 15 DOI: 10.1016/j.jcat.2017.09.011 | ||||
| Tags | Epoxidation, Heterogeneous catalysis, Hydrogen peroxide, Kinetics, Mechanism, Mesoporous niobium silicate | ||||
| Authors |
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| Affiliations |
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Funding (2)
| 1 | Federal Agency for Scientific Organizations | 0303-2016-0005 |
| 2 | Russian Foundation for Basic Research | 16-03-00827 |
Abstract:
Nb-containing mesoporous silicates reveal superior activity and selectivity in epoxidation of alkenes using hydrogen peroxide as green oxidant and, in contrast to mesoporous titanium-silicates, catalyze epoxidation of both electron-rich and electron-deficient C=C bonds. This report describes a kinetic and mechanistic investigation of epoxidation of two representative substrates, cyclooctene (CyO) and 2-methyl-1,4-naphthoquinone (MNQ), over two mesoporous niobium-silicates with predominantly di(oligo)meric or isolated Nb(V) sites. The observed kinetic regularities did not depend on the state of Nb but were strictly determined by the nature of the organic substrate. The rate law established for CyO is consistent with a mechanism that involves interaction of Н2О2 with Nb(V) sites to give a hydroperoxo species ‘NbOOH’ and water, followed by oxygen transfer to nucleophilic С=С bond, producing epoxide and regenerating the initial state of the catalyst. This mechanism is strongly supported by stereospecificity in epoxidation of cis-alkenes and high heterolytic pathway selectivity in the oxidation of cyclohexene. The ‘NbOOH’ species is manifested by an absorption feature at 307 nm in diffuse reflectance UV-vis spectra. The addition of base (NaOAc) causes shift of the absorption band to 293 nm and produces a rate-retarding effect on the epoxidation reaction. Several lines of evidence, including zero reaction order in MNQ, rate-accelerating effect of base, detection of acetamide in the reaction mixture, negligible reaction rate in ethylacetate, and recognition of weak basic sites in the niobium-silicates using infrared spectroscopy of adsorbed CDCl3, all indicate the MNQ epoxidation proceeds by another mechanism that involves rate-limiting oxidation of the solvent molecule (MeCN) to generate peroxycarboximidic acid, which reacts with electron-deficient C=C bond, producing epoxy derivative and acetamide.
Cite:
Ivanchikova I.D.
, Skobelev I.Y.
, Maksimchuk N.V.
, Paukshtis E.A.
, Shashkov M.V.
, Kholdeeva O.A.
Toward Understanding the Unusual Reactivity of Nb-Containing Catalysts in Epoxidation of C=C Bonds with Hydrogen Peroxide
Journal of Catalysis. 2017. V.356. P.85-99. DOI: 10.1016/j.jcat.2017.09.011 WOS Scopus РИНЦ ANCAN OpenAlex
Toward Understanding the Unusual Reactivity of Nb-Containing Catalysts in Epoxidation of C=C Bonds with Hydrogen Peroxide
Journal of Catalysis. 2017. V.356. P.85-99. DOI: 10.1016/j.jcat.2017.09.011 WOS Scopus РИНЦ ANCAN OpenAlex
Dates:
| Submitted: | Jun 29, 2017 |
| Accepted: | Sep 15, 2017 |
| Published online: | Nov 6, 2017 |
| Published print: | Dec 1, 2017 |
Identifiers:
| Web of science: | WOS:000418223300009 |
| Scopus: | 2-s2.0-85032336253 |
| Elibrary: | 31082218 |
| Chemical Abstracts: | 2017:1696699 |
| Chemical Abstracts (print): | 168:285389 |
| OpenAlex: | W2768008091 |