AVS 52nd International Symposium
    Surface Science Monday Sessions
       Session SS2-MoM

Paper SS2-MoM7
Growth of WO@sub 3@ Clusters on TiO@sub 2@(110)-(1x1).

Monday, October 31, 2005, 10:20 am, Room 203

Session: Oxide Surface Structure and Characterization
Presenter: O.A. Bondarchuk, University of Texas at Austin
Authors: O.A. Bondarchuk, University of Texas at Austin
Z. Dohnalek, Pacific Northwest National Laboratory
B.D. Kay, Pacific Northwest National Laboratory
J. Kim, Pacific Northwest National Laboratory
J.M. White, University of Texas at Austin
Correspondent: Click to Email
Tungsten oxide clusters supported on Al@sub 2@O@sub 3@, SiO@sub 2@, ZrO@sub 2@ and TiO@sub 2@ are known to be catalytically active for a wide range of acid-catalyzed reactions including alcohol dehydrogenation, alkane hydrogenation, metathesis etc. In this work, we studied the growth of WO@sub 3@ nanoclusters on TiO@sub 2@(110)-(1x1) surface using STM. Submonolayer amounts of WO@sub 3@ were deposited on TiO@sub 2@(110) via direct, thermal evaporation from WO@sub 3@. Using XPS we have determined that WO@sub 3@ deposited on TiO@sub 2@(110) is thermally stable and remains fully oxidized up to 700 K. Atomically resolved studies of WO@sub 3@ deposited at room temperature on TiO@sub 2@(110) show only fuzzy, poorly defined features indicating that the clusters are only weakly bound to the substrate. Subsequent annealing to 600 K results in the formation of bright (WO@sub 3@)@sub x@ clusters that can be easily imaged. In case of low WO@sub 3@ coverages (< 0.25 ML) the STM images indicate that the majority of clusters have identical size (~0.6nm in apparent diameter) and position with respect to the substrate registry. The amount of deposited WO@sub 3@ from a quartz crystal microbalance measurement together with the observed cluster density yields the upper bound of x @<=@ 3 for the number of W atoms in each cluster. Additionally, annealed (WO@sub 3@)@sub x@ clusters exhibit preferential alignment across the Ti4+ rows suggesting attractive interactions between them.