Particle migration model and its limitations

Catalyst particle nucleation in the initial stages and their subsequent growth play an important role in catalytic mechanisms. In a model Pt/alumina catalyst, the general view is that the formation of particles is a stepwise process incorporating the following steps (Wynblatt and Gjostein 1975, Cottrell 1971) individual metal atoms (called monomers) transform to two-dimensional islands, which subsequently transform to three-dimensional clusters. These clusters eventually transform into finite-sized particles. 

A binary collision model has been developed for particles migrating over planar supports. The rate-controlling steps in these mechanisms are either particle 

In the case of supported metal particles, experimental studies of particle growth mechanisms can determine the type of ripening. Generally, studies on supported noble metallic catalysts at elevated temperatures ( 500°C) indicate atomic diffusion from smaller metal particles across the surface of the support to 

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