  Single-Atom Alloys (SAAs) are a special class of alloy surface catalysts that
offer well defined, isolated active sites in a more inert metal host. The
dopant sites are generally assumed to have little or no influence on the
properties of the host metal, and transport of chemical reactants and products
to and from the dopant sites is generally assumed to be facile. Here, by
performing density functional theory calculations and surface science
experiments, we identify a new physical effect on SAA surfaces, whereby
adsorption is destabilised by up to 300 meV on host sites within the perimeter
of the reactive dopant site. We identify periodic trends for this behaviour,
and demonstrate a zone of exclusion around the reactive sites for a range of
adsorbates and combinations of host and dopant metals. Experiments confirm an
increased barrier for CO diffusion towards the dopant on a RhCu SAA. This
effect offers new possibilities for understanding and designing active sites
with tunable energetic landscapes surrounding them.
