2 research outputs found
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 [11Ģ
0] 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
Bimetallic NickelāCobalt Nanosized Layers Supported on Polar ZnO Surfaces: MetalāSupport Interaction and Alloy Effects Studied by Synchrotron Radiation X-ray Photoelectron Spectroscopy
The interaction of ultrathin bimetallic NiāCo
layers (0.25
and 1.5 nm) supported on polar (0001)ĀZnāZnO and (0001Ģ
)ĀOāZnO
substrates was investigated by synchrotron-based photoelectron spectroscopy
(PES) under ultrahigh vacuum (UHV) and O<sub>2</sub> environments.
Monometallic Ni and Co layers were also characterized to highlight
the influence of NiāCo synergetic effects on the metalāsupport
interaction. At room temperature, cobalt is partially oxidized, while
nickel is metallic. The effect of ZnO surface termination is minor,
while the influence of surface hydroxyl groups is discussed. Annealing
at 773 K in UHV promotes oxidation of monometallic Ni and Co layers
but has little influence on bimetallic NiāCo. In addition,
significant agglomeration of the NiāCo overlayer is observed,
with a parallel increase in the surface Co concentration. Agglomeration
of NiāCo is more pronounced on O-terminated ZnO. Upon annealing
in 1 Ć 10<sup>ā6</sup> mbar of O<sub>2</sub>, both Ni
and Co readily oxidize and redisperse over the ZnO substrate. Moreover,
cobalt tends to segregate over nickel, creating a concentration gradient
between the two alloy constituents (probably a coreāshell-like
structure). Overall, our results indicate that the interaction at
the NiāCo/ZnO interface is influenced by the synergetic effects
between the two metals and to a lesser extent by the substrate termination.
Taking into account the substantial progress made in the synthesis
of ZnO nanostructures and surfaces, this study can assist in the effort
toward improved ZnO-based catalysts with tailored properties