Physicochemical characterization of Au/CeO ₂ solids. Part 2: The impregnation preparation method

Au/CeO ₂ solids with different gold contents were prepared using the impregnation method. Electron microscopy (SEM and TEM) studies indicated the formation of both nanoparticles and large gold particles on the surface of the ceria support. SEM and XRD analyses revealed that the number and size of large particles increases with the gold content in the solid. The XPS technique showed that 90% of the total gold is in the metallic form Au ⁰ while the remaining 10% were cationic gold species Au ⁺. These latter were formed following calcination under dry air at 400 °C and are located in the proximity of the O ^2- and/or Cl ^- present on the support. These Au ⁺ species are present at the edge of gold particles and they were reduced into metallic gold when the solid was vacuum treated (5-7.10 ^-4 mbar) at 400 °C for 1 h. When air was adsorbed at room temperature on the latter vacuum treated solids, two EPR signals were obtained. The first one was assigned to O ₂ ^- species whereas attributing the second signal was difficult and required a more detailed investigation that will be presented in a forthcoming work.