Showing papers by "Mika Valden published in 1998"

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

Abstract: Gold clusters ranging in diameter from 1 to 6 nanometers have been prepared on single crystalline surfaces of titania in ultrahigh vacuum to investigate the unusual size dependence of the low-temperature catalytic oxidation of carbon monoxide. Scanning tunneling microscopy/spectroscopy (STM/STS) and elevated pressure reaction kinetics measurements show that the structure sensitivity of this reaction on gold clusters supported on titania is related to a quantum size effect with respect to the thickness of the gold islands; islands with two layers of gold are most effective for catalyzing the oxidation of carbon monoxide. These results suggest that supported clusters, in general, may have unusual catalytic properties as one dimension of the cluster becomes smaller than three atomic spacings.

Structure–Activity Correlations for Au Nanoclusters Supported on TiO2

Abstract: The catalytic performance of reducible metal-oxide-supported Au nanoclusters displays striking dependencies on several factors such as dispersion, support, pretreatment, and preparation methods. Planar model Au/TiO2 catalysts have been prepared in ultrahigh vacuum in order to investigate the strong size dependence of low-temperature CO oxidation. It is demonstrated that the experimentally observed structure sensitivity of CO oxidation on Au/TiO2 may be rationalized by a quantum size effect. Via scanning tunneling microscopy and spectroscopy (STM/STS) and elevated pressure reaction kinetics measurements, we show that a clear correlation exists between the structural, electronic, and reactivity properties of supported Au nanoclusters.