Morphology and CO Oxidation Reactions on Anion Doped CeO_XF_Y/Rh(111) and CeO_X/Rh(111) Inverse Catalysts

Doping cerium oxide with additives is a common procedure that improves stability of cerium oxide-based catalysts. We prepared fluorine-doped cerium oxide samples in the form of inverse catalysts on Rh(111) and compared their electronic, chemical, and morphological properties with fluorine-free CeO_X samples. By means of X-ray photoelectron spectroscopy (XPS), we followed the formation of oxygen vacancies and the depletion of fluorine after exposure of CeO_XF_Y to CO and O₂ gases at elevated temperatures. According to Ce 3d XPS spectra, the ability to create oxygen vacancies is not altered by fluorine atoms. Our results from low energy electron diffraction (LEED) and atomic force microscopy (AFM) show that fluorine affects mainly the morphology of the layers. Unlike the CeO₂ layers, fluorine-doped samples form 3D islands, which are partially rotated with respect to Rh [11̅0] direction due to stretching of the lattice constant caused by cerium oxide reduction. The possibility for creation stable Ce³⁺ sites without reducing the oxygen storage capacity makes anion doping a perspective tool for defect engineering in cerium oxide-based catalysts.