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Morphology and CO Oxidation Reactions on Anion Doped CeO<sub>X</sub>F<sub>Y</sub>/Rh(111) and CeO<sub>X</sub>/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<sub>X</sub> 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<sub>X</sub>F<sub>Y</sub> to CO and O<sub>2</sub> 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 CeO<sub>2</sub> 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 Ce<sup>3+</sup> sites without reducing the oxygen
storage capacity makes anion doping a perspective tool for defect
engineering in cerium oxide-based catalysts