Electrochemical Investigation of Photooxidation Processes Promoted by Sulfo-polyoxometalates: Coupling of Photochemical and Electrochemical Processes into an Effective Catalytic Cycle
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- 作者：Thomas Rü ; ther ; Victoria M. Hultgren ; Brian P. Timko ; Alan M. Bond ; William R. Jackson ; and Anthony G. Wedd
- 刊名：Journal of the American Chemical Society
- 出版年：2003
- 出版时间：August 20, 2003
- 年：2003
- 卷：125
- 期：33
- 页码：10133 - 10143
- 全文大小：242K
- 年卷期：v.125,no.33(August 20, 2003)
- ISSN：1520-5126
文摘
Oxidative photocurrents measured upon irradiation by a 7-W visible light (wavelength 312-700nm) demonstrated that the sulfo-polyoxometalate anion clusters [S2W18O62]4- (1a), [S2Mo18O62]4- (1b), and[SMo12O40]2- (2) may be activated photochemically to oxidize the organic substrates benzyl alcohol, ethanol,and (-)-menthol. In the case of catalytic photooxidation of benzyl alcohol to benzaldehyde in the presenceof 1a, quantitative electrochemical methods have identified pathways for the oxidation of reduced forms of1 generated during the catalysis. More generally, the oxidation pathways P(n+2)- + 2H+ 
Pn- + H2 and2P(n+2)- + O2 + 4H+ 2Pn- + 2H2O have been evaluated by monitoring acidified acetonitrile solutions ofthe 2e--reduced clusters by rotating disk electrode voltammetry under anaerobic and aerobic conditions,respectively. Neither of the reduced forms 1b(2e-) nor 2(2e-) reacted under these conditions. In contrast,1a(2e-) was oxidized via both pathways, consistent with its more negative redox potential, with the rate ofoxidation by air-oxygen being significantly faster than that by H+. The present work demonstrated that thecrucial step necessary to oxidize reduced catalyst in photocatalytic reactions involving the anions studiedmay be achieved or accelerated by application of an external potential more positive than the first redoxpotential of the polyoxometalate anion. Voltammetric analysis revealed that this in situ electrolyticregeneration of the reduced catalyst is an option that leads to a viable photoelectrocatalytic pathway, evenwhen the H+ and O2 pathways are not available.
Pn- + H2 and2P(n+2)- + O2 + 4H+ 2Pn- + 2H2O have been evaluated by monitoring acidified acetonitrile solutions ofthe 2e--reduced clusters by rotating disk electrode voltammetry under anaerobic and aerobic conditions,respectively. Neither of the reduced forms 1b(2e-) nor 2(2e-) reacted under these conditions. In contrast,1a(2e-) was oxidized via both pathways, consistent with its more negative redox potential, with the rate ofoxidation by air-oxygen being significantly faster than that by H+. The present work demonstrated that thecrucial step necessary to oxidize reduced catalyst in photocatalytic reactions involving the anions studiedmay be achieved or accelerated by application of an external potential more positive than the first redoxpotential of the polyoxometalate anion. Voltammetric analysis revealed that this in situ electrolyticregeneration of the reduced catalyst is an option that leads to a viable photoelectrocatalytic pathway, evenwhen the H+ and O2 pathways are not available.