Multicenter active sites of vanadium-substituted polyoxometalate catalysts on benzene hydroxylation with hydrogen peroxide and two reaction types with and without an induction period
✍ Scribed by Kenji Nomiya; Yukihiro Nemoto; Takeshi Hasegawa; Shin Matsuoka
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 311 KB
- Volume
- 152
- Category
- Article
- ISSN
- 1381-1169
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✦ Synopsis
Benzene hydroxylation with hydrogen peroxide catalyzed by selectively site-substituted vanadium V polyoxometalates was classified into two reaction types based on the turnover vs. time curve with or without an induction period. A prototypic example was the catalysis by the two geometrical isomers of trivanadium-substituted Keggin-type polyoxotungstate; w x 7y w x 7y a-1,2,3-SiW V O with a longer induction period and b-1,2,3-SiW V O without an induction period, respec-9 3 40 9 3 40 2 2 15 2 62 oxovanadium species generated from polyoxometalates, the reactions using NaVO or Na VO in water with varied pH 3 3 4
were examined. Under the acidic conditions there was no induction period, while under the neutral conditions there was a distinct induction period. The 51 V NMR measurements showed that the reactive species participating in these two reactions Ž . q Ž . y were VO O and VO O , respectively.