Reaction sites in CO oxidation were studied at the steady state over steppe
d Pt(113)=(s)2(111)x(001) by angular and velocity distributions of desorbin
g product CO2. Two reaction sites, (111) and (001) sites, are operative. Th
e (111) site preference is suppressed with increasing CO pressure in the ac
tive region where the reaction is roughly first order in CO. The preference
is reversed to the (001) site fairly below critical CO pressures where the
reaction begins to be retarded by CO. Below 500 K, on the other hand, the
site switching does not proceed quickly. The translational energy of CO2 is
characteristic of each site throughout the site switching. O 1999 Elsevier
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