Surface Defect-mediated Reactivity of Au/TiO 2 (110)
- PDF / 536,752 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 6 Downloads / 190 Views
R4.6.1
Surface Defect-mediated Reactivity of Au/TiO2(110) Ken T. Park,1,2 Minghu Pan,1 Vincent Meunier,3 William Shelton,3 Sergei Kalinin,4 Arthur P. Baddorf,4 and E.W. Plummer1,4 1 Department of Physics and Astronomy, The University of Tennessee Knoxville, TN 37996, U.S.A. 2 Department of Physics, Baylor University Waco, TX 76798, U.S.A. 3 Computer Science and Mathematics Division, Oak Ridge National Laboratory Oak Ridge, TN 37831, U.S.A. 4 Condensed Matter Sciences Division, Oak Ridge National Laboratory Oak Ridge, TN 37831, U.S.A. ABSTRACT Metal clusters supported by transition metal oxides, as exemplified by the Au/TiO2 system, have found broad applications as catalytic and sensor materials. The unusual properties of these systems originate from the specific interactions of metal clusters mediated by an oxide substrate, including local reduction below the cluster. In this work, we present recent results on the local interactions between one-dimensional defects on a TiO2 surface and their reactivity with oxygen and Au nano-clusters studied by a combination of Scanning Tunneling Microscopy and Spectroscopy (STM/S). High-resolution STM images, interpreted with first-principles theory, show that the observed one-dimensional strands have partially reduced Ti atoms coordinated above three-coordinated, surface oxygen atoms. When strands are exposed to 5 x 10-7 Torr O2 at 300 K, oxygen is adsorbed and randomly nucleated on and along the strands. The results indicate the presence of exposed Ti that act as an active site for oxygen adsorption even at room temperature. Gold nano-particles of diameters 5 nm and less have also been deposited on the sub-stoichiometric rows of TiOx and characterized by STM. Like point defects and step edges on TiO2(110), the strands serve as nucleation sites for gold nano-clusters. The 1D defects of the surface are interpreted in terms of a surface crystallographic shear type structure, in contrast to the proposed Ti2O3 added row model by Onish and Iwasawa [Phys. Rev. Lett. 76, (1996) 791]. The implications of this behavior and specific interaction between gold clusters, defects and gas molecules for catalytic activity of the Au/TiO2 system are discussed. INTRODUCTION Since unexpected catalytic activity by highly dispersed gold was reported [1], metal nanoparticles supported by transition metal oxides have been under intense spotlight. Among those investigated, Au nano-particles on the rutile TiO2(110) remains one of the most widely studied systems. In searching the origin of the catalytic properties exhibited by Au nano-particles, a variety of ideas and combinations thereof have been proposed [2]. For example, in CO oxidation Au rafts of about 3.5 nm-diameter (2-3 atoms thick) were reported to be most active, and the structure was correlated with distinctive electronic properties [3]. An anionic gold species has also been proposed for the active sites, which would allow the adsorption of oxygen and subsequent activation or possibly dissociation [4]. Other explanations involved the Au particl
Data Loading...
