Size-selected Au and Ag nanoclusters on rutile TiO2 (110) (1x1) surfaces probed by UHV-STM

PHYS 342

Steven K. Buratto,, Xiao Tong,, Lauren Benz, Steeve Chrétien, Paul Kemper,, Horia Metiu,, and Michael T. Bowers, Department of Chemistry and Biochemistry, University of California, Santa Barbara, Santa Barbara, CA 93106-9510
Catalysis of the oxidation of CO and small olefins by Aun and Aun nanoclusters on oxide supports is known to be strongly dependent on the size of the cluster and its interaction with the oxide surface. In our group we have probed this size dependence by depositing size-selected clusters of Agn+ and Aun+ (n = 1-7) from the gas phase onto single crystal rutile TiO2 (110) (1x1) surfaces at room temperature under soft-landing (< 2 eV/atom) conditions. We analyze the clusters on the surface using ultra-high vacuum scanning tunneling microscopy (UHV-STM) and compare the resulting structures with theory. In the case of Au+ , Ag+ and Ag2+ clusters deposited under soft-landing conditions we observe large, sintered clusters indicating high mobility for these species on the surface. For Aun+ (n > 1) and Agn+ (n > 2) clusters deposited under soft-landing conditions, however, we observe a high density of intact clusters bound to the surface and no sintered clusters indicating that these species have very limited mobility on the surface. For the intact clusters we can also observe the binding site and geometry of the cluster in the STM image and compare these with structures calculated using density functional theory (DFT) as well as with structures observed in the gas phase. In addition, we have shown through voltage-dependent STM and scanning tunneling spectroscopy (STS) that the surface electronic structure is significantly perturbed by adsorption of metal nanoclusters and that this perturbation is size dependent. Finally, we have performed temperature-programmed desorption (TPD) and temperature-programmed reaction (TPR) experiments on our nanocluster-decorated surfaces in order to probe the size-dependent chemistry of our model catalysts.

Fundamentals of Metal Oxide Catalysis
1:20 PM-4:40 PM, Wednesday, 13 September 2006 Grand Hyatt San Francisco -- Portrero, Oral

Division of Physical Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006