Comparison of Two Preparation Methods in the Redox Properties of Pd/CeO2/Ta/Si Model Catalysts: Spin Coating Versus Sputter Deposition

Abstract

Pd/CeO 2 /Ta/Si model catalysts were prepared by spin coating and sputter deposition method, and characterized by means of AFM, SEM and in situ XPS, especially focusing on the redox properties of Ce and Pd elements. Compared with thin CeO 2 films (about 2.2 nm), the thicker ones (about 22 nm) maintained Ce 4þ oxidation state even after treatment with H 2 up to 500°C while the presence of Pd facilitated the reduction of ceria. The reduction of ceria brought about following that of PdO, which was explained by the spillover of hydride in Pd to CeO 2 originating from hydrogen adsorption on the Pd surface. Compared with the sputter deposition method, spin coating produced the smaller size of Pd particles, thus leading to formation of the stable PdO species against hydrogen. Based on these results, a schematic model of Pd/CeO 2 /Ta/Si was suggested and it might be assumed that spin coating method provided with an environment similar to the conventional impregnation.