Preparation And Characterization Of FeO_x/Rh(111)and CoO_x/Rh(111) Model Catalysts

The chemical reactions occur at the surface of the catalysts,whose size,structure and composition determine the catalytic properties.However,the real catalysts are usually complex and electrically insulating,inhibiting the application of,for example,EELS,STM and AFM.Information on the surface state of a catalyst cannot be obtained.Thus,one has to resort to models in order to do surface science on catalysts.The models catalyst can be applied to study effects of particle size on the adsorption and desorption of gases,and on the catalytic activity and selectivity,and also to investigate possible roles of the support in adsorption and catalysis.We prepared the model surfaces of FeO_x,-/Rh(111)and CoO_x/Rh(111)in an ultrahigh vacuum(UHV)chamber.We use XPS and LEIS as tools to study the surface:(1)1 ML FeO thin films were grew by repeatedly depositing iron onto the Rh(111)surface at 1023k in 1x10-7 Torr O2 and sequentially oxidizing at the same condition for 10 minutes.After one monolayer,the 3D Fe2O3 occurs.The Fe2O3 thin films were grew by repeatedly depositing iron with substrate at 623 K in 1x10-6 Torr O2 and sequentially oxidizing at 623 K in 1x10-6 Torr O2 for 10 minutes.The prepared iron oxides thin film is reversible for different oxidation temperature.(2)CO3O4 thin film with layer-by-layer growth mode was prepared.The prepared thin film changed from CO3O4 to CoO,then Co with much higher oxidation or annealing temperature.