AVS 50th International Symposium
    Surface Science Monday Sessions
       Session SS3-MoA

Paper SS3-MoA4
Dimethyl Methylphosphonate Decomposition on Supported Ni Nanoparticles Deposited on a TiO@sub 2@(110) Surface

Monday, November 3, 2003, 3:00 pm, Room 328

Session: Structure and Reactivity of Metal Clusters
Presenter: J. Zhou, University of South Carolina
Authors: J. Zhou, University of South Carolina
Y.C. Kang, University of South Carolina
K. Varazo, University of South Carolina
D.A. Chen, University of South Carolina
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Sizes and structures of oxide-supported metal nanoparticles are very important in determining their catalytic reactivity. In our study, the thermal decomposition of dimethyl methylphosphonate (DMMP) on supported nickel nanoparticles has been investigated as a model system to understand the relationship between the particle size and reactivity. All the experiments were performed under UHV conditions by scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). Our STM studies show that various sizes of Ni particles with uniform particle size distributions can be prepared on TiO@sub 2@(110) surface by varying the diffusion (D) to deposition flux (F). The most uniform size distribution of Ni nanoparticles can be obtained with the lowest D/F ratio. XPS and TPD studies indicate that mainly molecular DMMP adsorbs on the supported Ni nanoparticles at room temperature. Between room temperature and 800 K, the adsorbed DMMP decomposes to produce H@sub 2@ and CO as primary gaseous products and CH@sub 4@ and HCHO as minor products. After heating to 800 K, all carbon desorbs from the surface while atomic phosphorous still remains. DMMP decomposition on various sizes of Ni nanoparticles as well as on the bulk Ni surface will be compared. Furthermore, studies of DMMP reaction will be also carried out on the supported Pt nanoparticles.