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The Fe IV O • oxyl unit as a key intermediate in water oxidation on the Fe III hydroxide: DFT predictions
Author(s) -
Shubin Aleksandr A.,
Kovalskii Viktor Yu.,
Ruzankin Sergey Ph.,
Zilberberg Igor L.,
Parmon Valentin N.,
Tomilin Felix N.,
Avramov Pavel V.
Publication year - 2021
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.26610
Subject(s) - chemistry , hydroxide , oxygen , nucleophile , molecule , dissociation (chemistry) , catalysis , crystallography , hydroxylation , medicinal chemistry , inorganic chemistry , stereochemistry , photochemistry , organic chemistry , enzyme
The OO coupling process in water oxidation on the gamma FeOOH hydroxide catalyst is simulated by means of density functional theory using model iron cubane cluster Fe 4 O 4 (OH) 4 . A key reactive intermediate is proposed to be the HOFe IV O• oxyl unit with terminal oxo radical. The “initial” vertex Fe III (OH) moiety forms this intermediate at the calculated overpotential of 0.93 V by adding one water molecule and withdrawing two proton–electron pairs. The OO coupling goes via water nucleophilic attack on the oxyl oxygen to form the OO 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 Fe IV 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 OO coupling. Nevertheless, being more effective for ferryl oxygen, the hydroxylation in fact enhances selectivity of the OO coupling initiated by the oxyl oxygen.