(520b) In Situ Grown Metal Nanoparticle Catalysts: Properties and Control

The ability to produce supported metal nanoparticle catalysts via exsolution from a perovskite type oxide support under reducing conditions has been known for some time and is used in some formulations of automotive emissions control catalysts. The ability to re-dissolve and exsolve the metal via redox cycling has led to these systems being referred to as smart or regenerable catalysts. While this phenomenon is well known, the mechanism by which the transition metal is exsolved from the oxide host is still poorly understood. The relationships between the exsolution process and the resulting structure of the metal nanoparticles are also not well understood. In this talk I will discuss our recent mechanistic studies of the exsolution process. Using well-defined model systems and detailed structural analysis by electron microscopy and atomic force microscopy, the nucleation and exsolution of Ni particles from Ni-doped strontium titanate was monitored. These studies show how exsolution produces unique surface structures consisting of metal particles partially submerged in pits on the oxide surface. I will show that this particle-in-a-pit morphology imparts unusually high thermal stability as well as significantly decreased carbon filament formation. Metal exsolution control will be discussed for host oxide lattices in thin film form.