CO adsorption on a Au/CeO2 (111) model catalyst

We prepared a Au/CeO2 (111) model catalyst by depositing a thin cerium oxide film on a Ru(0001) surface and subsequently depositing gold. This model system was investigated using high-resolution photoemission spectroscopy. Gold forms metallic nanoparticles on CeO2 with an average particle size that depends on the Au dose. At 80 K adsorption of CO was observed on the supported Au particles, which induces a chemical shift of +0.9 eV in the An 4f level of the An atoms directly involved in the Au-CO bond. CO adsorption also induces an additional, particle-size-dependent shift, which affects all Au atoms in the particle; i.e., the whole Au particle is affected by CO adsorption. The fraction of surface atoms involved in CO bonding decreases with increasing gold particle size, from similar to 60-70% for small particles to 15-20% for large particles. It is concluded that CO only adsorbs on defects (low-coordinated Au atoms). The CO desorption temperature decreases with increasing particle size. This is explained as follows: on small particles the most abundant defects are corner atoms and kinks (6-coordinated), which interact strongly with CO. On large particles the most abundant defects are edges between two planes (7-coordinated), which interact less strongly with CO.