AVS 51st International Symposium
    Applied Surface Science Thursday Sessions
       Session AS-ThA

Paper AS-ThA3
Physical and Chemical Properties of Ce@sub1-x@Zr@subx@O@sub2@ Nanoparticles and Ce@sub1-x@Zr@subx@O@sub2@(111) Surfaces: Synchrotron-based Studies

Thursday, November 18, 2004, 2:40 pm, Room 210A

Session: Fuel Cell, Catalytic, and Nanomaterials Characterization
Presenter: X. Wang, Brookhaven National Laboratory
Authors: X. Wang, Brookhaven National Laboratory
J.A. Rodriguez, Brookhaven National Laboratory
G. Liu, Brookhaven National Laboratory
J.C. Hanson, Brookhaven National Laboratory
J. Hrbek, Brookhaven National Laboratory
C.H.F. Peden, Pacific Northwest National Laboratory
A. Iglesias-Juez, Instituto de Catálisis y Petroleoquímica, CSIC, Spain
M. Fernández-García, Instituto de Catálisis y Petroleoquímica, CSIC, Spain
Correspondent: Click to Email
The physical and chemical properties of Ce@sub1-x@Zr@subx@O@sub2@ nanoparticles and Ce@sub1-x@Zr@subx@O@sub2@(111) surfaces (x@<=@0.5) were investigated with synchrotron-based techniques (high-resolution photoemission, time-resolved X-ray diffraction and X-ray absorption near-edge spectroscopy). CeO@sub2@ and Ce@sub1-x@Zr@subx@O@sub2@ particles in sizes between 3 and 7 nm were synthesized using a novel microemulsion method. The results of XANES (O K-edge, Ce and Zr LIII-edges) indicate that the Ce@sub1-x@Zr@subx@O@sub2@ nanoparticles and Ce@sub1-x@Zr@subx@O@sub2@(111) surfaces have very similar electronic properties. The lattice constant decreased with increasing Zr content, varying from 5.40Å in CeO@sub2@ to 5.27Å in Ce@sub0.5@Zr@sub0.5@O@sub2@. 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 Ce@sub1-x@Zr@subx@O@sub2@ compounds. The nanoparticles were more reactive towards H@sub2@ and SO@sub2@ than the (111) surfaces. The Ce@sub1-x@Zr@subx@O@sub2@(111) surfaces did not reduce in hydrogen at 300°C. At temperatures above 250°C, the Ce@sub1-x@Zr@subx@O@sub2@ nanoparticles reacted with H@sub2@ and water evolved into gas phase. XANES showed the generation of Ce@super3+@ cations without reduction of Zr@super4+@. There was an expansion in the unit cell of the reduced nanoparticles probably as a consequence of a partial Ce@super4+@-->Ce@super3+@ transformation and the sorption of hydrogen into the material. S K-edge XANES spectra pointed to SO@sub4@ as the main product of the adsorption of SO@sub2@ on the Ce@sub1-x@Zr@subx@O@sub2@ nanoparticles and Ce@sub1-x@Zr@subx@O@sub2@(111) surfaces. Full dissociation of SO@sub2@ was seen on the nanoparticles but not on the (111) surfaces. The metal cations at corner and edge sites of the nanoparticles probably play a very important role in interactions with the H@sub2@ and SO@sub2@ molecules.