Electron-accepting surface properties of ceria–(praseodymia)–zirconia solids modified by Y 3+ or La 3+ studied by paramagnetic probe method

• Published in: Applied surface science Vol. 207; no. 1; pp. 100 - 114
• Main Authors: Ikryannikova, Larisa N, Markaryan, Goar L, Kharlanov, Andrey N, Lunina, Elena V
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 2003
• Subjects: Ceria; Electron-acceptor sites; EPR spectroscopy; Paramagnetic probe; Praseodymia; Surface; Zirconia; Zirconia; Ceria; Praseodymia; Electron-acceptor sites; Paramagnetic probe; EPR spectroscopy; Surface
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/S0169-4332(02)01332-6

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, La 0.1)Ce x Zr 1− x O 2− y ( x=0.1–0.7), Y 0.1Pr 0.3Zr 0.6O 2− y and Y 0.1Pr 0.15Ce 0.15Zr 0.7O 2− y mixed oxides. Two types of acceptor sites—coordinatively unsaturated (cus) cations Zr 4+ and Ce 4+—have been revealed on the CeO 2–ZrO 2 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 trivalent Y 3+ or La 3+ cations reduces the amount of electron-acceptor sites belonging to cerium cations, stabilizing ones as Ce 3+. A formation of very strong electron-accepting sites (Pr 4+ 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 Zr 4+ cationic sites on Y 0.1Pr 0.3Zr 0.6O 2− y and Y 0.1Pr 0.15Ce 0.15Zr 0.7O 2− 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 Zr 3+ 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.