W. Vogel, N. Alonso-Vante / Journal of Catalysis 232 (2005) 395–401
401
tion period (time = 81 min) and persists for a certain period,
even when the O2 partial pressure is lowered to O2/CO = 0.5
subsurface oxygen species play a decisive role in this differ-
ence. More experiments of this type are of course needed to
get a full understanding of the underlying mechanisms (e.g.,
for CO oxidation). In these experiments it would be impor-
tant to avoid conditions that lead to particle agglomeration,
since meaningful data can be gained only at a constant dis-
persion of the active catalyst surface.
(
Fig. 6). Further work is needed to understand this phenom-
enon.
4
.2. Solid/liquid interface
The surface reaction toward CO oxidation onto Rux(Xyl)
and Rux(Dcb) on the solid/gas interface reflects, to some
extent, a similar behavior when such surfaces form an elec-
trochemical interface (solid/liquid). In fact, as reported in
an earlier work [9], a striking difference in charge stored
in the electrochemical double layer between the “reduced”
states, that is, of Rux(Xyl) and Rux(Dcb), was observed.
More charges (ca. 10 times) are accumulated on Rux(Xyl)
than on Rux(Dcb). Such an effect can be due to the fact that
the species present in the electrolyte (e.g., H , OH ) inter-
act differently (adsorption process) according to the state of
electrode surface, leading to so-called pseudocapacitance.
On the other hand, it was observed that the amount of CO
adsorbed to Rux(Xyl) in an electrochemical cell was also
higher than adsorbed to Rux(Dcb) [7]. Since the measured
COads vibration frequency from FTIR measurements, in re-
flexion mode, was similar on the two samples, we arrive at
the conclusion that the CO species adsorb easily to Rux(Xyl)
by displacing. other molecules responsible for the stored
charge (pseudocapacitance) in the double layer. This phe-
nomenon also takes place, although to a lesser extent, on
the oxidized material. This complex interplay between the
species in the electrolyte and the state of the surface of
Ru nanoparticle reflects the catalytic behavior depicted in
Figs. 1, 3, 5, and 6.
Acknowledgments
N.A.V. expresses his thanks to the Alexander von Hum-
boldt Stiftung and the Max Planck Society for funding his
stay at the Fritz-Haber-Institut. The authors are grateful to
Drs. V. Le Rhun and A.C. Boucher for their technical assis-
tance in the sample preparation.
+
−
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