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Sintering, oxidation, and chemical properties of size-selected nickel clusters on TiO2,,110...

Summary: Sintering, oxidation, and chemical properties of size-selected nickel
clusters on TiO2,,110...
Masato Aizawa, Sungsik Lee, and Scott L. Andersona)
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112
Received 11 March 2002; accepted 12 June 2002
We report a study of Nin /TiO2 samples prepared by size-selected deposition of Nin (n
1,2,5,10,15) on rutile TiO2(110). The effects of deposition energy and support preparation
conditions on the oxidation state of the clusters are examined by x-ray photoelectron spectroscopy
XPS . On the stoichiometric surface, Nin is stable, but oxidation can be driven by increased impact
energy. For TiO2 surfaces with chemisorbed oxygen, deposited Nin are oxidized even at low impact
energies. Low energy ion scattering spectroscopy was used to characterize the dispersion of Ni on
the support, and provide some insight into binding morphology. Small clusters bind preferentially to
oxygen sites. Large clusters bind in compact geometries and appear to retain some three dimensional
character on the surface. The data suggest that the clusters neither fragment, nor agglomerate, in
room temperature deposition. Temperature programmed desorption TPD of CO was used to
characterize deposited clusters. For these small clusters, no strong desorption features are observed
in the temperature range above 140 K, where CO desorbs from TiO2 . The lack of CO binding is
discussed in terms of strong Ni­TiO2 binding. The ion scattering data indicate that there is
significant sintering, and possibly partial encapsulation, of the Ni clusters during the TPD
experiments. XPS reveals little change in oxidation state. This is the first study where the oxidation


Source: Anderson, Scott L. - Department of Chemistry, University of Utah


Collections: Energy Storage, Conversion and Utilization; Materials Science; Chemistry