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Title: Structural and redox properties of ceria in alumina-supported ceria catalyst supports

Abstract

Several alumina-supported ceria samples with varying ceria contents (1, 2, 10, and 39 wt%) have been studied by different techniques (XRD, Raman, TEM-EDS, UV-vis DRS, XANES, and EPR), aiming to establish a complete model on the structural and redox characteristics of ceria entities in these samples. Two general types of ceria entities are observed: aggregated crystalline ceria species (3D-Ce) and dispersed ceria species in the form of two-dimensional patches (2D-Ce). The relative amounts of each of these species do not show a linear relationship with the cerium loading: as the cerium content is increased, a trend toward formation of 3D-Ce, to the detriment of 2D-Ce, is observed. The EPR data evidence differences in chemical (redox) behavior between 2D-Ce, 3D-Ce, and unsupported ceria. Thus, the main differing characteristic of some 3D-Ce particles with respect to unsupported ceria, which holds true for all 3D-Ce formed with weight percent {le} 10, is the absence of associated vacancies upon outgassing at 773 K (evidenced by EPR of chemisorbed oxygen). This behavior is attributed to the existence of an epitaxial relationship between ceria and the underlying alumina, which influences largely the properties of relatively small 3D-Ce particles. In the initial calcined state, 2D-Ce patches aremore » shown to present cerium in a (formally) Ce{sup 4+} oxidation state, with relaxed coordination distances and experiencing a decreased ligand field which facilitates their reduction (in comparison with 3D-Ce or unsupported ceria). Implications of these results on molecular design of depollution catalysts are discussed.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
CSIC, Madrid (ES)
OSTI Identifier:
20050840
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical
Additional Journal Information:
Journal Volume: 104; Journal Issue: 17; Other Information: PBD: 4 May 2000; Journal ID: ISSN 1089-5647
Country of Publication:
United States
Language:
English
Subject:
33 ADVANCED PROPULSION SYSTEMS; 54 ENVIRONMENTAL SCIENCES; CERIUM OXIDES; ALUMINIUM OXIDES; CATALYST SUPPORTS; CRYSTAL STRUCTURE; CATALYTIC CONVERTERS

Citation Formats

Martinez-Arias, A., Fernandez-Garcia, M., Salamanca, L.N., Valenzuela, R.X., Conesa, J.C., and Soria, J. Structural and redox properties of ceria in alumina-supported ceria catalyst supports. United States: N. p., 2000. Web. doi:10.1021/jp992796y.
Martinez-Arias, A., Fernandez-Garcia, M., Salamanca, L.N., Valenzuela, R.X., Conesa, J.C., & Soria, J. Structural and redox properties of ceria in alumina-supported ceria catalyst supports. United States. doi:10.1021/jp992796y.
Martinez-Arias, A., Fernandez-Garcia, M., Salamanca, L.N., Valenzuela, R.X., Conesa, J.C., and Soria, J. Thu . "Structural and redox properties of ceria in alumina-supported ceria catalyst supports". United States. doi:10.1021/jp992796y.
@article{osti_20050840,
title = {Structural and redox properties of ceria in alumina-supported ceria catalyst supports},
author = {Martinez-Arias, A. and Fernandez-Garcia, M. and Salamanca, L.N. and Valenzuela, R.X. and Conesa, J.C. and Soria, J.},
abstractNote = {Several alumina-supported ceria samples with varying ceria contents (1, 2, 10, and 39 wt%) have been studied by different techniques (XRD, Raman, TEM-EDS, UV-vis DRS, XANES, and EPR), aiming to establish a complete model on the structural and redox characteristics of ceria entities in these samples. Two general types of ceria entities are observed: aggregated crystalline ceria species (3D-Ce) and dispersed ceria species in the form of two-dimensional patches (2D-Ce). The relative amounts of each of these species do not show a linear relationship with the cerium loading: as the cerium content is increased, a trend toward formation of 3D-Ce, to the detriment of 2D-Ce, is observed. The EPR data evidence differences in chemical (redox) behavior between 2D-Ce, 3D-Ce, and unsupported ceria. Thus, the main differing characteristic of some 3D-Ce particles with respect to unsupported ceria, which holds true for all 3D-Ce formed with weight percent {le} 10, is the absence of associated vacancies upon outgassing at 773 K (evidenced by EPR of chemisorbed oxygen). This behavior is attributed to the existence of an epitaxial relationship between ceria and the underlying alumina, which influences largely the properties of relatively small 3D-Ce particles. In the initial calcined state, 2D-Ce patches are shown to present cerium in a (formally) Ce{sup 4+} oxidation state, with relaxed coordination distances and experiencing a decreased ligand field which facilitates their reduction (in comparison with 3D-Ce or unsupported ceria). Implications of these results on molecular design of depollution catalysts are discussed.},
doi = {10.1021/jp992796y},
journal = {Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical},
issn = {1089-5647},
number = 17,
volume = 104,
place = {United States},
year = {2000},
month = {5}
}