Mechanism of the Formation of O2? Radical Anions on CeO2 and (0.5–10)%CeO2/ZrO2 during the Adsorption of an NO-O2 Mixture |
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Authors: | A N Ilichev M D Shibanova A A Ukharskii A M Kuli-zade and V N Korchak |
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Institution: | (1) Semenov Institute of Chemical Physics, Russian Academy of Sciences, Moscow, 119991, Russia |
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Abstract: | It is established by ESR that the adsorption of an NO + O2 mixture at 20°C on oxidized CeO2 (O2, T = 400–700°C) produces radical anions O
2
−
located both on isolated Ce4+ cations (O
2
−
(1)) and in associated anionic vacancies (O
2
−
(2)). These species differ in thermal stability. For example, O
2
−
(2) decomposes at 20°C, while O
2
−
(1) decomposes at 50°C. Only O
2
−
(1) species are observed at −196°C in ZrO2-supported CeO2. In the case of NO + O2 adsorption at 20°C, O
2
−
is stabilized on Zr4+ cations and decomposes at 270°C. Increasing the cerium oxide content of the ZrO2 surface from 0.5 to 10% only partially inhibits the formation of O
2
−
-Zr4+. The Zr4+ cation is shown to possess a higher Lewis acidity than the Ce4+ cation, and the ionic bond in O
2
−
-Zr4+ complexes is stronger than that in O
2
−
-Ce4+ complexes. ESR, temperature-programmed desorption, and IR spectroscopic data for various adsorption complexes of NO on CeO2 suggest that, in the key step of O
2
−
formation, free electrons appear on the surface owing to the conversion of adsorbed NO molecules into nitrito chelates on coordinately unsaturated ion pairs Ce4+-O
2
−
.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 414–422.Original Russian Text Copyright © 2005 by Il’ichev, Shibanova, Ukharskii, Kuli-zade, Korchak. |
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Keywords: | |
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