title: Electronic structure controls reactivity of size-selected Pd clusters adsorbed on TiO2 surfaces.
abstract: The catalytic activity of metal clusters of different sizes adsorbed on oxide surfaces can be explored systematically by using model catalysts. We studied the temperature-programmed reaction of CO with O2 catalyzed by Pd clusters (Pd(n), for n = 1, 2, 4, 7, 10, 16, 20, and 25) that were size-selected in the gas phase and deposited on rutile TiO2(110). X-ray photoemission spectroscopy revealed that the Pd 3d binding energy varied nonmonotonically with cluster size and that the changes correlated with strong size variations in CO oxidation activity. Taking final-state effects into account, low activity was correlated with higher-than-expected Pd 3d binding energy, which is attributed to a particularly stable valence electronic structure; electron transfer from the TiO2 support to the Pd clusters also occurs. Ion scattering shows that small clusters form single-layer islands on the surface and that formation of a second layer begins to occur for clusters larger than Pd10.
authors.affiliation: Department of Chemistry, University of Utah, 315 South 1400 East, Room 2020, Salt Lake City, UT 84112-0850, USA.
authors.forename: William E
authors.initials: WE
authors.lastname: Kaden
authors.forename: Tianpin
authors.initials: T
authors.lastname: Wu
authors.forename: William A
authors.initials: WA
authors.lastname: Kunkel
authors.forename: Scott L
authors.initials: SL
authors.lastname: Anderson