A surface science study of model catalysts. 2. Metal-support interactions in Cu/SiO2 model catalysts

The thermal stability of wet-chemically prepared Cu/SiO2 model catalysts co ntaining nanometer-sized Cu particles on silica model supports was studied upon heating in hydrogen and ultrahigh vacuum. The surface and interface ph enomena that occur are determined by the metal-support interactions. Heatin g in hydrogen results in a reduction of the metal-support interaction and s intering occurs via Cu particle migration at 350 degrees C. Annealing in ul trahigh vacuum up to 620 degrees C does not result in sintering of the Cu p articles. 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 pl ace. For a 400-500 nm thick SiO2 layer, Cu silicide islands are formed by r eaction between Cu and SiO2, which can be regenerated by exposure to air at room temperature for several hours. The importance of the preparation proc edure 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.