Communication: Suppression of sintering of size-selected Pd clusters under realistic reaction conditions for catalysis.

The stability of model catalysts based on size-selected Pd clusters supported on graphite surfaces has been explored under realistic conditions for catalytic oxidation of methane at mild temperatures. The experimental results show that aggregated films of nanoparticles are highly unstable, but clusters pinned to the surface in the submonolayer coverage regime are much more stable against sintering. The degree of sintering of the pinned clusters, which does occur, proceeds by the release of clusters from their pinning sites. The suppression of sintering depends on the cluster deposition energy with respect to the pinning threshold.