AVS 59th Annual International Symposium and Exhibition
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP37
Ag Nanoparticles on Reducible CeO2(111) Thin Films: Effect of Nanoscale Ceria

Tuesday, October 30, 2012, 6:00 pm, Room Central Hall

Session: Surface Science Poster Session
Presenter: S.W. Hu, University of Science and Technology of China
Authors: S.W. Hu, University of Science and Technology of China
X.F. Feng, University of Science and Technology of China
D.D. Kong, University of Science and Technology of China
D.L. Cheng, University of Science and Technology of China
Y.F. Ye, University of Science and Technology of China
J.F. Zhu, University of Science and Technology of China
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Ag/CeO2 is of particular interests because of its importance in technical applications as catalysts for many chemical reactions such as CO and hydrocarbon oxidation. However, there are still some discrepancies remaining in the fundamental recognition of the Ag/CeO2 catalysts such as the oxidation state of Ag species and the mechanism of Ag-induced the reduction of CeO2.In order to obtain a detailed insight of the Ag/CeO2 system, the growth and structures of Ag nanoparticles on CeOx(111) thin films with different thicknesses, morphologies and reduction degrees have been systematically studied by scanning tunneling microscopy(STM), X-ray photoelectron spectroscopy (XPS) and low energy electron diffraction (LEED). These CeOx(111) thin films were epitaxially grown on Cu(111). It is found that in most cases Ag exhibits the three-dimensional (3D) growth with constant particle densities on the CeOx(111) surfaces. Ag only populates the sites at the ceria-ceria step edges, independent of the thicknesses and the reduction degree of the ceria films. Moreover, the particle density is directly proportional to the number of step edges of ceria, which is related to its thickness on Cu(111). On the reduced ceria films, Ag nanoparticles do not nucleate on point defects. Upon heating, the Ag nanoparticles undergo serious sintering before desorption at 800 K on the fully oxidized CeO2 films. While on the reduced ceria films,the sintering and desorption process are slowed down at the same annealing temperatures as those on CeO2. This result suggests that although the surface point defects have no influence on the growth behavior of Ag, they can enhance the thermal stability by inhibiting the diffusion of Ag on the ceria surface to form large particles during annealing.