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−xO2−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 trivalent 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 Y0.1Pr0.15Ce0.15Zr0.7O2−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.