Redox Behavior of Thermally Aged Ceria−Zirconia Mixed Oxides. Role of Their Surface and Bulk Structural Properties

Redox Behavior of Thermally Aged Ceria−Zirconia Mixed Oxides. Role of Their Surface and Bulk Structural Properties. Yeste, M. P., Hernández, J. C., Bernal, S., Blanco, G., Calvino, J. J., Pérez-Omil, J. A., & Pintado, J. M. Chemistry of Materials, 18(11):2750–2757, may, 2006.

Paper doi abstract bibtex

The relationship existing between aging conditions, redox behavior, and surface/bulk structural properties of two thermally aged ceria-zirconia mixed oxides, CZ-MO and CZ-SO, is analyzed. The samples were prepared by applying to a fresh Ce0.62Zr0.38O2 mixed oxide two alternative aging routines consisting of a reduction with H2 at 1223 K (5 h), followed by either a mild, CZ-MO, or severe, CZ-SO, re-oxidation treatment. By combining high-resolution electron microscopy and a number of chemical charcterization techniques, it is shown that the nanostructure of the aged oxides, specifically the total amount and surface presence of the phase exhibiting an ordered cationic sublattice ($ąppa$-like phase), is a key factor in determining their redox response. In the low-temperature reduction range (Tredn ≤ 773 K), the enhanced reducibility of the CZ-MO sample is proposed to be kinetically controlled by its surface structure mainly consisting of the $ąppa$-like phase. In accordance with the reported results, the surface activation of the H2 molecule, much faster on the CZ-MO sample, is proposed to be the rate controlling step of the overall reduction process. This proposal was further confirmed by the dramatic downward shift observed in the temperature-programmed reduction diagrams recorded for the corresponding oxide-supported rhodium samples. By contrast, in the high-temperature reduction range (Tredn ≥ 973 K), the observed difference of reducibility, higher in the case of the CZ-MO sample, is interpreted as due to thermodynamic factors related to the nature of the predominant cationic sublattice structure, ordered for CZ-MO and disordered in the case of the CZ-SO sample. \textcopyright 2006 American Chemical Society.

@article{Yeste2006,
abstract = {The relationship existing between aging conditions, redox behavior, and surface/bulk structural properties of two thermally aged ceria-zirconia mixed oxides, CZ-MO and CZ-SO, is analyzed. The samples were prepared by applying to a fresh Ce0.62Zr0.38O2 mixed oxide two alternative aging routines consisting of a reduction with H2 at 1223 K (5 h), followed by either a mild, CZ-MO, or severe, CZ-SO, re-oxidation treatment. By combining high-resolution electron microscopy and a number of chemical charcterization techniques, it is shown that the nanostructure of the aged oxides, specifically the total amount and surface presence of the phase exhibiting an ordered cationic sublattice ($\kappa$-like phase), is a key factor in determining their redox response. In the low-temperature reduction range (Tredn ≤ 773 K), the enhanced reducibility of the CZ-MO sample is proposed to be kinetically controlled by its surface structure mainly consisting of the $\kappa$-like phase. In accordance with the reported results, the surface activation of the H2 molecule, much faster on the CZ-MO sample, is proposed to be the rate controlling step of the overall reduction process. This proposal was further confirmed by the dramatic downward shift observed in the temperature-programmed reduction diagrams recorded for the corresponding oxide-supported rhodium samples. By contrast, in the high-temperature reduction range (Tredn ≥ 973 K), the observed difference of reducibility, higher in the case of the CZ-MO sample, is interpreted as due to thermodynamic factors related to the nature of the predominant cationic sublattice structure, ordered for CZ-MO and disordered in the case of the CZ-SO sample. {\textcopyright} 2006 American Chemical Society.},
author = {Yeste, Mar{\'{i}}a Pilar and Hern{\'{a}}ndez, Juan Carlos and Bernal, Seraf{\'{i}}n and Blanco, Ginesa and Calvino, Jos{\'{e}} J. and P{\'{e}}rez-Omil, Jos{\'{e}} A. and Pintado, Jos{\'{e}} M.},
doi = {10.1021/cm060635i},
issn = {0897-4756},
journal = {Chemistry of Materials},
month = {may},
number = {11},
pages = {2750--2757},
title = {{Redox Behavior of Thermally Aged Ceria−Zirconia Mixed Oxides. Role of Their Surface and Bulk Structural Properties}},
url = {http://www.scopus.com/inward/record.url?eid=2-s2.0-33744974809{\&}partnerID=tZOtx3y1},
volume = {18},
year = {2006}
}

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