Synergetic Catalysis of Copper and Iron in Oxidation of Reduced Keggin Heteropolytungstates by Dioxygen

Abstract

Polyoxometalates (POMs) and in particularly Keggin heteropolytungstates are much studied and commercially important catalysts for dioxygen-based oxidation processes. The rate-limiting step in many POM-catalyzed O-based oxidations is reoxidation of the reduced POM by O. We report here that this reoxidation process, as represented by the one-electron-reduced Keggin complexes POM (α-PWO and α-SiVWO) reacting with O, is efficiently catalyzed by a combination of copper and iron complexes. The reaction kinetics and mechanism have been comprehensively studied in sulfate and phosphate buffer at pH 1.8. The catalytic pathway includes a reversible reaction between Cu(II) and Fe(II), followed by a fast oxidation of POM by Fe(III) and Cu(I) by O to regenerate Fe(II) and Cu(II). The proposed reaction mechanism quantitatively describes the experimental kinetic curves over a wide range of experimental conditions. Since the oxidized forms, α-PWO and α-SiVWO, are far better oxidants of organic substrates than the previously studied POMs, α-SiWO and α-AlWO, this synergistic Fe/Cu cocatalysis of reduced-POM reoxidation could well facilitate significant new O/air-based processes.

H5PV2Mo10O40 Polyoxometalate Encapsulated in NU-1000 Metal–Organic Framework for Aerobic Oxidation of a Mustard Gas Simulant

“…With substrates possessing aromatic functionality, this reduction typically occurs via electron transfer from the aromatic ring to the POM . With alkyl substrates, electrochemical reduction or sacrificial reductant ,, can be used to prime the POM for reaction with molecular oxygen. Here, we selected isobutyraldehyde as a sacrificial reductant.…”

Photocatalytic Multielectron Reduction of Nitroarenes to Anilines by Utilizing an Electron-Storable Polyoxometalate-Based Metal–Organic Framework

“…33,34 In particular, when in the dark for 20 min, POM red is reoxidized with air. 35,36 The good photochromic performance of {ZnW-TPT} is beneficial for the photocatalysis.…”

Redox-Active Zeolitic Transition Metal Oxides Based on ε-Keggin Units for Selective Oxidation

“…Transition metals are able to store and transfer electrons, 17 and the multicomponent would enhance the ability. 18,19 Therefore, design and synthesis of redox-active zeolitic transition metal oxides are desired for catalytic oxidation. Herein, we reported the synthesis, structural characterization, redox property, and catalytic application of zeolitic transition metal oxides based on iron molybdates (MoFe 0.22 O).…”

“…O 2 activation via an electron-transfer-based redox process is more important and generally includes two steps: (1) substrate oxidation by catalysts and (2) catalysts reoxidation with O 2 . Transition metals are able to store and transfer electrons, and the multicomponent would enhance the ability. , Therefore, design and synthesis of redox-active zeolitic transition metal oxides are desired for catalytic oxidation.…”