Oxidation of Reduced Keggin Heteropolytungstates by Dioxygen in Water Catalyzed by Cu(II)

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• 作者：Mooeung Kim ; Ira A. Weinstock ; Yurii V. Geletii ; Craig L. Hill
• 刊名：ACS Catalysis
• 出版年：2015
• 出版时间：December 4, 2015
• 年：2015
• 卷：5
• 期：12
• 页码：7048-7054
• 全文大小：426K
• ISSN：2155-5435

文摘

The reaction of reduced polyoxometalates (POMs) with dioxygen is centrally important in POM catalysis. We report that this process, as represented by the one-electron-reduced Keggin complexes POM_red (伪-AlW₁₂O₄₀^{6鈥?/sup>, 伪-SiW₁₂O₄₀5鈥?/sup>, and 伪-PW₁₂O₄₀4鈥?/sup>), is efficiently catalyzed by copper complexes. The Cu-catalyzed pathway is dominant in the presence of as low as 鈭?.1 渭M of Cu, a copper concentration that is typically lower than the copper ion contamination in aqueous solutions. The reaction kinetics and mechanism have been comprehensively studied in sodium sulfate buffer at pH 2.0. The catalytic pathway includes a reversible reduction of Cu(II) by POM_red, followed by a fast reoxidation of Cu(I) by O₂ to regenerate Cu(II). The rate constants of the first catalytic steps were determined by three approaches and found to be (1.8 卤 0.3) 脳 105 and 57 卤 15 M鈥? s鈥? for SiW₁₂O₄₀5鈥?/sup> and PW₁₂O₄₀4鈥?/sup>, respectively. These reactions are thermodynamically more favorable and therefore proceed significantly more quickly than those for the direct outer-sphere electron transfer to O₂. The proposed reaction mechanism quantitatively describes the experimental kinetic curves over a wide range of experimental conditions.}