Onset of Catalytic Activity of Gold Clusters on Titania with the Appearance of Nonmetallic Properties

Rainer D. R., Xu C., Goodman D. W., J. Mol. Catal. A Chem. 119, 307 (1997).

S. C. Street and D. W. Goodman The Chemical Physics of Solid Surfaces D. A. King and D. P. Woodruff Eds. (Elsevier Amsterdam 1997) vol. 8 p. 375.

Goodman D. W., J. Phys. Chem. (Centennial Ed.) 100, 13090 (1996).

Haruta M., Catal. Catal. Today 36, 153 (1997).

Huber H., McIntosh D., Ozin G. A., Inorg. Chem. 16, 975 (1977).

Haruta M., et al., J. Catal. 144, 175 (1993).

Bamwenda G. R., Tsubota S., Nakamura T., Haruta M., Catal. Lett. 44, 83 (1997).

The experiments were carried out in a combined elevated-pressure reactor–ultrahigh vacuum (UHV) system with a base pressure of 5 × 10 −11 Torr equipped with a double-pass cylindrical mirror analyzer for Auger electron spectroscopy (AES) and XPS measurements a quadrupole mass analyzer and a UHV-STM (Omicron) [

Campbell R. A., Goodman D. W., Rev. Sci. Instrum. 63, 172 (1992);

]. After preparation and characterization in the UHV chamber the Au/TiO 2 (110) model catalyst was transferred in situ into the reaction chamber through a double-stage differentially pumped Teflon sliding seal. This arrangement facilitates elevated-pressure adsorption studies in the pressure range of 1 × 10 −8 to 1 × 10 3 Torr. A TiO 2 (110) single crystal (Commercial Crystal Laboratories) an n -type semiconductor after cycles of Ar + -ion bombardment and vacuum annealing at 700 to 1100 K was found to be sufficiently conductive for electron spectroscopy and STM studies. This cleaning procedure produces a slightly oxygen-deficient surface with a well-ordered (1×1) surface as characterized by LEED and XPS measurements [

Pan J.-M., Maschhoff B. L., Diebold U., Madey T. E., J. Vac. Sci. Technol. A 10, 2470 (1992);

Zhang L., Persaud R., Madey T. E., Phys. Rev. B 56, 10549 (1997);

]. Gold clusters were evaporated onto the TiO 2 (110) surface from a source containing high-purity Au wire wrapped around a W filament that was heated resistively. The Au flux was calibrated with a Re(0001) subtrate by using AES and STM as described (13). The Au coverage is reported in monolayers (ML) one ML corresponding to 1.387 × 10 15 atoms per centimeter squared. After the Au deposition the sample was annealed at 850 K for 2 min. The sample temperature was measured with a pyrometer (OMEGA OS3700) which was calibrated against a W-5% Re/W-26% Re thermocouple. Research-grade CO was further purified by storing at liquid N 2 temperatures; O 2 was used as received. The CO:O 2 (2:1) mixture was prepared separately before the adsorption experiments.

Xu C., Lai X., Zajac G. W., Goodman D. W., Phys. Rev. B 56, 13464 (1997).

S. Pak M. Valden X. Lai D. W. Goodman in preparation.

Canning N. D. S., Outka D., Madix R. J., Surfactant Sci. 141, 240 (1984).

Iizuka Y., et al., Catal. Today 36, 115 (1997).

Xu C., Oh W. S., Liu G., Kim D. Y., Goodman D. W., J. Vac. Sci. Technol. A 15, 1261 (1997).

Pesty F., Steinrück H.-P., Madey T. E., Surfactant Sci. 339, 83 (1995).

Lin S. D., Bollinger M., Vannice M. A., Catal. Lett. 17, 245 (1993).

We acknowledge the support of this work by the Department of Energy Office of Basic Energy Sciences Division of Chemical Sciences the Robert A. Welch Foundation and the Dow Chemical Company. M.V. thanks the Academy of Finland for support as a Visiting Scientist.