S. Volkening et J. Wintterlin, CO oxidation on Pt(111) - Scanning tunneling microscopy experiments and Monte Carlo simulations, J CHEM PHYS, 114(14), 2001, pp. 6382-6395
The catalytic reaction between adsorbed oxygen atoms and CO molecules on Pt
(111) was investigated by scanning tunneling microscopy and modeled by Mont
e Carlo simulations. Experiments were performed by dosing preadsorbed O-ad
layers with CO between 237 and 274 K. Two stages were observed during dosin
g with CO, an initial reordering and compression of (2x2)O-ad islands, and
a subsequent shrinking of the islands by the reaction of O-ad to give CO2.
The reaction occurs exclusively at boundaries between (2x2)O-ad and c(4x2)C
Oad domains. The reaction order with respect to the oxygen coverage is 0.5;
the reactivity of the boundary increases during the reaction. The Monte Ca
rlo simulations included surface diffusion of O-ad atoms, attractive intera
ctions between O-ad atoms, the O-ad-COad reaction probability (with paramet
ers from quantitative scanning tunneling microscopy measurements), adsorpti
on/desorption of CO, and a high mobility of COad. The experimentally observ
ed domain shapes, the reaction order of 0.5, and the increasing boundary re
activity could only be reproduced by additionally including an O-ad coordin
ation-dependent activation energy DeltaE(react)* of 25 meV per O-ad neighbo
r that accounts for the attractive O-ad-O-ad interactions. The initial orde
ring stage could be modeled by incorporating an additional repulsive intera
ction between O-ad and COad. The fact that no reaction occurs in the interi
or of the (2x2)O-ad domains, although they are covered by a layer of inters
titial COad molecules, is attributed to the crucial role of reactive O-ad-C
Oad configurations that only exist at the domain boundaries. (C) 2001 Ameri
can Institute of Physics.