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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 Kovalskii,
  • Sergey Ruzankin,
  • Igor Zilberberg,
  • Valentin Parmon,
  • Felix Tomilin,
  • Paul Avramov
Alexander Shubin
Boreskov Institute of Catalysis SB RAS
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Viktor Kovalskii
Boreskov Institute of Catalysis SB RAS
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Sergey Ruzankin
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
Kirensky Institute of Physics SB RAS
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Paul Avramov
Kyungpook National University
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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.

Peer review status:IN REVISION

01 Jun 2020Submitted to International Journal of Quantum Chemistry
02 Jun 2020Assigned to Editor
02 Jun 2020Submission Checks Completed
24 Jun 2020Reviewer(s) Assigned
21 Jul 2020Review(s) Completed, Editorial Evaluation Pending
21 Jul 2020Editorial Decision: Revise Major