Physical and chemical properties of Ce1-xZrxO 2 nanoparticles and Ce1-xZrxO2(1 1 1) surfaces: Synchrotron-based studies

J. A. Rodriguez, X. Wang, G. Liu, J. C. Hanson, J. Hrbek, C. H.F. Peden, A. Iglesias-Juez, M. Fernández-García

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Abstract

In this article, we review a series of studies that use synchrotron-based techniques (high-resolution photoemission, time-resolved X-ray diffraction (XRD), and X-ray absorption near-edge spectroscopy) to investigate the physical and chemical properties of Ce1-xZrxO2 nanoparticles and Ce1-xZrxO2(1 1 1) surfaces (x ≤ 0.5). CeO2 and Ce1-xZrxO2 particles in sizes between 4 and 7 nm were synthesized using a novel microemulsion method. The results of XANES (O K-edge, Ce and Zr L III-edges) indicate that the Ce1-xZrxO 2 nanoparticles and Ce1-xZrxO2(1 1 1) surfaces have very similar electronic properties. For these systems, the lattice constant decreased with increasing Zr content, varying from 5.4 Å in CeO2 to 5.3 Å in Ce0.5Zr0.5O 2. Within the fluorite structure, the Zr atoms exhibited structural perturbations that led to different types of Zr-O distances and non-equivalent O atoms in the Ce1-xZrxO2 compounds. The Ce 1-xZrxO2 nanoparticles were more reactive towards H2 and SO2 than the Ce1-xZr xO2(1 1 1) surfaces. The Ce1-xZr xO2(1 1 1) surfaces did not reduce in hydrogen at 300°C. At temperatures above 250°C, the Ce1-xZr xO2 nanoparticles reacted with H2 and water evolved into gas phase. XANES showed the generation of Ce3+ cations without reduction of Zr4+. There was an expansion in the unit cell of the reduced nanoparticles probably as a consequence of a partial Ce 4+ → Ce3+ transformation and the sorption of hydrogen into the bulk of the material. S K-edge XANES spectra pointed to SO4 as the main product of the adsorption of SO2 on the Ce 1-xZrxO2 nanoparticles and Ce 1-xZrxO2(1 1 1) surfaces. Full dissociation of SO2 was seen on the nanoparticles but not on the Ce 1-xZrxO2(1 1 1) surfaces. The metal cations at corner and edge sites of the Ce1-xZrxO2 nanoparticles probably play a very important role in interactions with the H2 and SO2 molecules.

Original languageEnglish (US)
Pages (from-to)11-19
Number of pages9
JournalJournal of Molecular Catalysis A: Chemical
Volume228
Issue number1-2 SPEC. ISS.
DOIs
StatePublished - Mar 16 2005
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Process Chemistry and Technology
  • Physical and Theoretical Chemistry

Keywords

  • High-resolution photoemission
  • Nanoparticles
  • Time-resolved X-ray diffraction

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