The thermal stability of wet-chemically prepared Cu/SiO2 model catalysts containing nanometer-sized Cu particles on silica model supports was studied upon heating in hydrogen and ultrahigh vacuum. The surface and interface phenomena that occur are determined by the metal−support interactions. Heating in hydrogen results in a reduction of the metal−support interaction and sintering occurs via Cu particle migration at 350 °C. Annealing in ultrahigh vacuum up to 620 °C does not result in sintering of the Cu particles. When a 5 nm thin SiO2 layer on top of a Si(100) substrate is used as SiO2 model support, interdiffusion of Cu into the Si substrate takes place. For a 400−500 nm thick SiO2 layer, Cu silicide islands are formed by reaction between Cu and SiO2, which can be regenerated by exposure to air at room temperature for several hours. The importance of the preparation procedure for the strength of the metal−support interaction is discussed. This paper shows that the use of model catalysts to study surface and interface phenomena is relevant for technical heterogeneous metal catalysis.

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Cu/SiO2 model catalysts containing nanometer-sized Cu particles on a flat silica model support were wet-chemically prepared and characterized in detail by a variety of surface science techniques. The particle size and shape, particle number density, metal surface coverage, total metal loading, and oxidation state of the particles were determined by ultrahigh vacuum atomic force microscopy, electron microscopy, low-energy ion scattering, Rutherford backscattering spectrometry, and X-ray photoelectron spectroscopy. Deposition of a Cu precursor on a flat Si wafer with a SiO2 top layer by spin-coating was followed by calcination in air at 450 °C. This preparation method produces both homogeneously distributed hemispherical CuO particles with an average height of 8 nm and highly dispersed oxidic Cu species. Subsequent reduction in hydrogen at 250 °C results in metallic and more rounded Cu particles with an average height of 8 nm.

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