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Electron-accepting surface properties of ceria–(praseodymia)–zirconia solids modified by Y3+ or La3+ studied by paramagnetic probe method
EPR paramagnetic probe method with 2,2,6,6-tetramethylpiperidin-N-oxyl (TEMPO) as a probe has been applied to study of electron-accepting properties of the surface of (Y, La0.1)CexZr1-x)2-y (x = 0.1-0.7), Y0.1Pr0.3Zr0.6O2-y and Y0.1Pr0.15Ce0.15Zr0.7O2-y mixed oxides. Two types of acceptor sites-coor...
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Published in: | Applied surface science 2003-02, Vol.207 (1-4), p.100-114 |
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Main Authors: | , , , |
Format: | Article |
Language: | English |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | EPR paramagnetic probe method with 2,2,6,6-tetramethylpiperidin-N-oxyl (TEMPO) as a probe has been applied to study of electron-accepting properties of the surface of (Y, La0.1)CexZr1-x)2-y (x = 0.1-0.7), Y0.1Pr0.3Zr0.6O2-y and Y0.1Pr0.15Ce0.15Zr0.7O2-y mixed oxides. Two types of acceptor sites-coordinatively unsaturated (cus) cations Zr4+ and Ce4+-have been revealed on the CeO2-ZrO2 surface after thermovacuum treatment (820 K). The relative amounts and 'strength' of these centers were evaluated on the basis of EPR spectra analysis. An introduction of divalent Y3+ or La3+ cations reduces the amount of electron-acceptor sites belonging to cerium cations, stabilizing ones as Ce3+. A formation of very strong electron-accepting sites (Pr4+ cus cations) able to form charge transfer complexes with adsorbed TEMPO on the surface of praseodymia-containing samples after thermovacuum treatment was found out. At the same time electron-accepting ability of Zr4+ cationic sites on Y0.1Pr0.3Zr0.6O2-y and Y0.1Pr0.15CeM5Zr0.7O2-y surfaces decreases in comparison with ceria-zirconia one. The generally used IR spectroscopy technique with CO as a probe molecule appeared to be considerably less informative for such systems characterization, due to their high catalytic activity to carbon monoxide. A formation of paramagnetic Zr3+ ions in ceria-zirconia mixed oxides has been investigated by EPR spectroscopy technique. The different states of this paramagnetic ion are realized in the complex oxides depending on Ce/Zr ratio. |
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ISSN: | 0169-4332 |
DOI: | 10.1016/S0169-4332(02)01332-6 |