Article,
CO oxidation on Pt(111)---Scanning tunneling microscopy experiments and Monte Carlo simulations
J. Chem. Phys., 114 (14): 6382-6395 (2001)
DOI: 10.1063/1.1343836
Abstract
The catalytic reaction between adsorbed oxygen atoms and CO molecules
on Pt(111) was investigated by scanning tunneling microscopy and
modeled by Monte Carlo simulations. Experiments were performed by
dosing preadsorbed Oad layers with CO between 237 and 274 K. Two
stages were observed during dosing with CO, an initial reordering
and compression of (2�2)Oad islands, and a subsequent shrinking of
the islands by the reaction of Oad to give CO2. The reaction occurs
exclusively at boundaries between (2�2)Oad and c(4�2)COad domains.
The reaction order with respect to the oxygen coverage is 0.5; the
reactivity of the boundary increases during the reaction. The Monte
Carlo simulations included surface diffusion of Oad atoms, attractive
interactions between Oad atoms, the Oad�COad reaction probability
(with parameters from quantitative scanning tunneling microscopy
measurements), adsorption/desorption of CO, and a high mobility of
COad. The experimentally observed domain shapes, the reaction order
of 0.5, and the increasing boundary reactivity could only be reproduced
by additionally including an Oad coordination-dependent activation
energy DeltaE<sub>react</sub><sup>*</sup> of 25 meV per Oad neighbor
that accounts for the attractive Oad�Oad interactions. The initial
ordering stage could be modeled by incorporating an additional repulsive
interaction between Oad and COad. The fact that no reaction occurs
in the interior of the (2�2)Oad domains, although they are covered
by a layer of interstitial COad molecules, is attributed to the crucial
role of reactive Oad�COad configurations that only exist at the domain
boundaries.
Tags
- adsorbed
- carbon
- carlo
- catalysis;
- chemistry;
- compounds;
- diffusion;
- digital
- layers;
- methods;
- microscopy;
- monte
- oxidation;
- platinum
- scanning
- simulation;
- surface
- tunnelling
