IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Wednesday Sessions
       Session SS+SC-WeM

Paper SS+SC-WeM9
Electronic and Chemical Properties of Ce@sub 0.8@Zr@sub 0.2@O@sub 2@(111) Surfaces: Photoemission, XANES, Density Functional, and NO@sub 2@ Adsorption Studies

Wednesday, October 31, 2001, 11:00 am, Room 122

Session: Adsorption on Semiconductor and Metal Oxide Surfaces
Presenter: G. Liu, Brookhaven National Laboratory
Authors: G. Liu, Brookhaven National Laboratory
J.A. Rodriguez, Brookhaven National Laboratory
J. Hrbek, Brookhaven National Laboratory
J. Dvorak, Brookhaven National Laboratory
C.H.F. Peden, Pacific Northwest National Laboratory
Correspondent: Click to Email
Synchrotron-based photoemission,conventional XPS, XANES, and first-principles density functional (DF) calculations were used to study the electronic properties of a Ce@sub 0.8@Zr@sub 0.2@O@sub 2@ mixed-metal oxide. The results of DF calculations show that the band gap in bulk Ce@sub 0.8@Zr@sub 0.2@O@sub 2@ is ~ 0.6 eV smaller than in bulk CeO@sub 2@, with the Zr atoms in the mixed-metal oxide showing smaller positive charges than the cations in ZrO@sub 2@ or CeO@sub 2@. When present in a lattice of CeO@sub 2@, the Zr atoms are forced to adopt larger metal-O distances than in ZrO@sub 2@, leading to a reduction in the oxidation state of this element. Due to non-equivalent Zr-O distances, at least three different types of oxygen atoms are found in the Ce@sub 0.8@Zr@sub 0.2@O@sub 2@ system. O K-edge XANES spectra for a series of Ce@sub 1-x@Zr@sub x@O@sub 2@ (x=0, 0.1, 0.2, 0.3, 1) compounds show a distinctive line shape for the mixed-metal oxides that can not be attributed to a sum of CeO@sub 2@ and ZrO@sub 2@ features, supporting the idea that the O atoms in Ce@sub 1-x@Zr@sub x@O@sub 2@ are in a special chemical environment. XPS Ce 3d spectra show the presence of Ce@super 3+@ cations which may be related to the relative stability of oxygen vacancy defects upon incorporation of zirconia into ceria. The interaction of NO@sub 2@ gas with Ce@sub 0.8@Zr@sub 0.2@O@sub 2-x@(111), CeO@sub 2-x@(111), and Zr(Y)O@sub 2-x@(111) reduced surfaces was examined. Ne@super +@ ion sputtering was used to generate substantial concentrations of Ce@super 3+@, Zr@super 2+@ and Zr0 centers on the oxide surfaces. On CeO@sub 2-x@(111), NO@sub 3@, NO@sub 2@ and N were seen upon adsorption of NO@sub 2@. In contrast, only NO@sub 2@ and N were detected after adsorption of NO@sub 2@ on Ce@sub 0.8@Zr@sub 0.2@O@sub 2-x@(111) and Zr(Y)O@sub 2-x@(111). Adsorption of NO@sub 2@ induced an increase in the oxidation state of the metal cations (Ce@super 3+@ to Ce@super 4+@; Zr0 to Zr@super 2+@).