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Formation of oxygen active species in Ag-modified CeO2 catalyst for soot oxidation: A DFT study

Paper ID Volume ID Publish Year Pages File Format Full-Text
55667 47061 2011 8 PDF Available
Title
Formation of oxygen active species in Ag-modified CeO2 catalyst for soot oxidation: A DFT study
Abstract

In this paper, we analyze from a theoretical point of view, based on the existing literature and on specific first principles DFT calculations, some aspects of the reactivity of Ag-modified CeO2 surfaces used for soot combustion in particulate diesel filters. We have considered various species adsorbed and coadsorbed on the CeO2(1 1 1) stoichiometric and reduced surface: O2 molecules, small carbon clusters, isolated Ag atoms and small Ag clusters. Carbonaceous species react with the ceria surface with formation of oxygenated carbon fragments and subsequent formation of reduced ceria but the mechanism which occurs to replenish the oxygen content of the oxide catalyst is still unclear. The formation of peroxo and superoxo species is discussed. The role of silver in modifying the properties of CeO2(1 1 1) has also been considered. Ag atoms and Ag5 clusters act as donor species, become oxidized and donate the valence electron to the oxide with formation of reduced Ce3+ ions. A charge transfer in the opposite direction occurs when Ag atoms are bound to O vacancies. In the second case, we notice that in the presence of gas-phase oxygen the formation of superoxo species can be mediated by small Ag particles. However, the stronger affinity for oxygen of the vacancy compared to Ag always leads as a final result to filling the cavity by ambient oxygen.

Graphical abstractAg atoms and Ag5 clusters on the CeO2(1 1 1) surface act as donor species, become oxidized and donate an electron to the oxide with formation of reduced Ce3+ ions. A charge transfer in the opposite direction occurs when Ag atoms are bound to O vacancies. Their role in O2 activation is discussed.Figure optionsDownload full-size imageDownload high-quality image (144 K)Download as PowerPoint slideHighlights► Key aspects of the reactivity of Ag-modified CeO2 used for soot combustion in particulate Diesel filters are analyzed. ► Ag clusters become oxidized with formation of reduced Ce3+ ions. ► Formation of superoxo species can be mediated by small Ag particles.

Keywords
Ceria; DFT calculations; Silver clusters; Oxygen vacancy
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Formation of oxygen active species in Ag-modified CeO2 catalyst for soot oxidation: A DFT study
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Publisher
Database: Elsevier - ScienceDirect
Journal: Catalysis Today - Volume 177, Issue 1, 22 November 2011, Pages 31–38
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
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Online Support
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