  Density functional theory based calculations of the energetics of adsorption
and diffusion of CO on Pt islets and on the Ru(0001) substrate show that CO has
the lowest adsorption energy at the center of the islet, and its bonding
increases as it moves to the edge of the island and further onto the substrate.
Activation energy barriers for CO diffusion from the islet to the Ru surface
are found to be lower than 0.3 eV making the process feasible and leading to
the conclusion that this hydrogen oxidation catalyst is CO tolerant because of
the spillover of CO from active Pt sites to the Ru substrate. We present the
rationale for this effect using insights from detailed electronic structure
calculations.
