New reaction of anion radicals O − with water on the surface of FeZSM-5

Complexes of bivalent iron stabilized in the FeZSM-5 zeolite matrix ( α-sites) are known to be able to decompose nitrous oxide stoichiometrically to form oxygen anion radicals, O −, bound to iron ( α-oxygen), (Fe II) α + N 2O → (Fe III O −) α + N 2. Similar to O − radicals on V and Mo oxides, α-oxyg...

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Bibliographic Details
Published in:Journal of catalysis 2008-02, Vol.254 (1), p.110-120
Main Authors: Panov, Gennady I., Starokon, Eugeny V., Pirutko, Larisa V., Paukshtis, Eugeny A., Parmon, Valentin N.
Format: Article
Language:English
Subjects:
Anion radical O
Catalysis
Chemistry
DRIFT spectroscopy
FeZSM-5
Iron
N 2O
Oxidation
Photocatalytic oxidation
Water
α-Oxygen
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Summary:Complexes of bivalent iron stabilized in the FeZSM-5 zeolite matrix ( α-sites) are known to be able to decompose nitrous oxide stoichiometrically to form oxygen anion radicals, O −, bound to iron ( α-oxygen), (Fe II) α + N 2O → (Fe III O −) α + N 2. Similar to O − radicals on V and Mo oxides, α-oxygen is highly reactive in respect to CO, H 2, methane and other hydrocarbons. It participates in catalytic oxidation of benzene to phenol by nitrous oxide, providing selectivity close to 100%. In this work, adsorption measurements, IR spectroscopy, TPD, and isotope methods were used to describe an earlier unknown reaction of O − species with water, which proceeds at 5–200 °C via the hydrogen abstraction mechanism according to the equation 2(Fe III O −) α + H 2O → 2(Fe III OH −) α + (1/2)O 2. The reaction leads to the hydroxyl groups formed on α-sites, and equivalent amount of O 2 evolves into the gas phase from water. Desorption of the hydroxyl groups occurs at above 400 °C via their recombination into water and dioxygen, resulting in the reactivation of α-sites, 2(Fe III OH −) α → 2(Fe II) α + H 2O + (1/2)O 2. High sensitivity of α-oxygen to water admixtures may be an important factor explaining some contradictory results reported in the literature on the behavior of α-oxygen. Because α-oxygen is a typical representative of anion radicals O −, this reaction may be relevant not only to the conventional oxidation catalysis over zeolites and metal oxides, but also to photocatalytic processes, where formation of O − is well documented.
ISSN:0021-9517
1090-2694
DOI:10.1016/j.jcat.2007.12.001