Invited Paper SS2-MoA8
The Influence of Metal – Substrate Bonding Energetics on Metal Atom Adsorption, Cluster Nucleation and Film Growth

Monday, October 18, 2010, 4:20 pm, Room Santa Ana

Oxide-supported late transition metal nanoparticles form the basis for many important industrial catalysts. The activity, selectivity and sintering rates of these catalysts can depend strongly on the particle size, the oxide support, and the extent of reduction of the oxide. The microkinetics of sintering are essentially the same as for nucleation and growth. All of these kinetic properties are closely related to the variation of metal atom energy (chemical potential) with nanoparticle size. We will review our calorimetric measurements of the energies of metal atoms in nanoparticles supported on different oxide surfaces, and relate those to nucleation/growth kinetics. We will discuss these results in the light of DFT calculations by our collaborators, H. Jonsson, G. Henkelman and L. Xu. The stability of Ag nanoparticles increases with particle size on both MgO(100) and reduced CeO₂(111), until the number of atoms per particle exceeds ~5000. At any given size, Ag nanoparticles have much higher stability on reduced CeO₂(111) than on MgO(100). This difference is due to the much larger adhesion energy of Ag nanoparticles to reduced CeO₂(111) compared to MgO(100). Increasing the extent of reduction of the CeO₂ surface increases Ag particle stability. The energetics and growth of Li and Ca on MgO(100) are dominated by defect sites, and differences in migration barriers there. The migration rates of Pd clusters on MgO(100) vary in unusual ways with size below 5 atoms, and this impacts nucleation.

The above results for oxide surfaces will be contrasted with similar studies of metal film growth on polymer surfaces, where diffusion of metal atoms below the surface and highly exothermic reactions with subsurface heteroatoms can dominate the early stages of growth.

Work supported by NSD and DOE-OBES.