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The FeIV-O● oxyl unit as a key intermediate in water oxidation on the FeIII-hydroxide: DFT predictions
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  • Alexander Shubin,
  • Viktor KovalskiiOrcid,
  • Sergey RuzankinOrcid,
  • Igor Zilberberg,
  • Valentin Parmon,
  • Felix TomilinOrcid,
  • Paul Avramov
Alexander Shubin
Boreskov Institute of Catalysis SB RAS
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Viktor Kovalskii
Orcid
Boreskov Institute of Catalysis SB RAS
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Sergey Ruzankin
Orcid
Boreskov Institute of Catalysis SB RAS
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Igor Zilberberg
Boreskov Institute of Catalysis SB RAS
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Valentin Parmon
Boreskov Institute of Catalysis SB RAS
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Felix Tomilin
Orcid
Kirensky Institute of Physics SB RAS
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Paul Avramov
Kyungpook National University
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Peer review status:UNDER REVIEW

01 Jun 2020Submitted to International Journal of Quantum Chemistry
02 Jun 2020Assigned to Editor
02 Jun 2020Submission Checks Completed
24 Jun 2020Reviewer(s) Assigned

Abstract

The O-O coupling process in water oxidation on the gamma FeOOH hydroxide catalyst is simulated by means of density functional theory using model iron cubane cluster Fe4O4(OH)4. A key reactive intermediate is proposed to be the HO-FeIV-O• oxyl unit with terminal oxo radical formed from vertex HO-FeIV-OH moiety by withdrawal of proton-electron pair. The O-O coupling goes via water nucleophilic attack on the oxyl oxygen to form the O-O bond with a remarkably low barrier of 11 kcal/mol. This process is far more effective than alternative scenario based on direct interaction of two ferryl FeIV=O sites (with estimated barrier of 36 kcal/mol) and is comparable with the coupling between terminal oxo center and three-coordinated lattice oxo center (12 kcal/mol barrier). The process of hydroxylation of terminal oxygen inhibits the O-O coupling. Nevertheless, being more effective for ferryl oxygen, the hydroxylation in fact enhances selectivity of the O-O coupling initiated by the oxyl oxygen.