Regensburg 2004 – wissenschaftliches Programm

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O: Oberflächenphysik

O 25: Epitaxie und Wachstum II

O 25.6: Vortrag

Dienstag, 9. März 2004, 17:00–17:15, H39

Thin TiO₂ films and Au/TiO₂ on Ru (0001) studied by XPS and CO-TPD — •Zhong Zhao, H. Rauscher, and R.J. Behm — University of Ulm

The chemical composition and adsorption behavior of well-defined TiO₂ films on Ru (0001) of up to 20 ML thickness and Au/TiO₂/Ru(0001) model catalysts are characterized by XPS and CO-TPD. The TiO₂ films were grown under UHV conditions, Au was deposited by evaporation (T_sub =300K). XPS shows that titania grows on Ru (0001) as either well oxidized TiO₂ or reduced TiO₂ (mixture of TiO₂ and Ti₂O₃), depending on the preparation method. Neither CO₂ production, nor CO dissociation is observed when CO desorbs from surfaces on the Au/TiO₂/Ru model catalyst (d_Au =2-3 nm). CO desorbs completely at around 275 K from nanometer-sized Au clusters supported on reduced TiO₂. As the Au coverage is increased from 0.3 ML to 2 ML, the peak temperature shifts from around 219 K to 197 K, equivalent to a decrease in CO adsorption energy from 60 to 54 kJ/mol ( v = 10¹⁴ s⁻¹). After annealing the catalyst to 770 K, the amount of adsorbed CO decreases significantly; corresponding STM measurements indicate a significant increase of the Au cluster size. Neither encapsulation of the Au clusters by reduced titanium oxides nor Au oxidation were observed after annealing. CO adsorption on the titania film itself does not change significantly in the presence of Au clusters.