Electron-accepting surface properties of ceria–(praseodymia)–zirconia solids modified by Y3+ or La3+ studied by paramagnetic probe method

Abstract 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 0.1 Pr 0.3 Zr 0.6 O 2− y and Y 0.1 Pr 0.15 Ce 0.15 Zr 0.7 O 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 0.1 Pr 0.3 Zr 0.6 O 2− y and Y 0.1 Pr 0.15 Ce 0.15 Zr 0.7 O 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.