CRYSTALLINE AND ELECTRONIC STRUCTURE OF GOLD NANOCLUSTERS DETERMINED BY EXAFS, XRD AND XPS METHODS

Gold particles nanoclusters as supported catalysts were analyzed by extended X-ray absorption fine structure, X-ray diffraction and X-ray photoelectron spectroscopy in order to determine their local, global and electronic structure. The present study points out the strong deformation of the local structure of the active metal due to its interaction with oxide supports as well as a possible oxidation state of the gold component. The average particle size and the microstrain parameters of the supported Au nanoclusters were determined by X-ray diffraction method, based on the Fourier transform of the experimental X-ray line profiles. The global structure is obtained with a fitting method using of the generalized Fermi function facilities for the approximation technique. The strong interaction between the metal nanoclusters and oxide supports induces a great change in the local and global microstructures of the catalysts, modifying at the same time the chemisorptions and catalytic processes that occur at the Au-support interface. The following catalyst samples were investigated: Au/ZnO/MgO/Al 2 O 3 , Au/CuO/Al 2 O 3 and Au/Li 2 O/CeO 2 /Al 2 O 3 . The XPS technique was used for determining the electronic states of gold, gold oxide and metal oxides in the oxide supports.