electrocatalysis on surfaces modified... - Brookhaven National ...

catalytic effect observed at very positive potentials (0.7V). The catalysis has been
ascribed to the adatom-mediated oxygen transfer with a possible electronic effect for As
[111]. Similar behavior is observed with Sb, which decreases the adsorption of CO on
Pt(100) and Pt(111) surfaces by removing the two-fold bridging geometry, as deduced
from the relative ν CO band intensities [72]. At the saturation Sb coverage only linear CO
is observed.
Baltruschat and coworkers [112] reported a large negative shift of CO oxidation
to 0.25V caused by Sn adsorbed at step sites on Pt (332) and Pt(755) stepped surfaces
(Fig. 16.10). Sn adsorbs preferentially at the step sites, which can be deduced from the
inhibition of H adsorption on the step sites from voltammetry curves [113]. The effect
has been ascribed to a destabilization of the CO molecules due to repulsion between CO
and Sn. This repulsion shifts the CO molecules into a so-called “high coverage” state,
which can be oxidized at low potentials as shown for Pt-Sn alloy surfaces [114]. (This
state is not formed in oxidation of methanol on this alloy, which was offered as an
explanation of the inhibition effect observed in that reaction.) The CO oxidation rates at
low potentials are, however, very sluggish. The effect of Sn on the reaction on Pt(111)
was found to be negligible. The activity of stepped Pt surfaces is certainly related to the
observed effect of Sn on polycrystalline Pt [91], which usually has a high density of
steps.
16.3.2.4 Other organic molecules
In addition to the oxidation of formic acid and methanol, the oxidation of a
considerable number of organic molecules is catalyzed by metal adlayers on Pt [1,2].
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