Surface migration and spontaneous monolayer dispersion of compounds onto supports

It is well known that surface migration of diffusion plays an important role in catalysis and catalyst preparation. For example, sintering of a catalyst may occur by surface migration of atoms during a sufficiently high-temperature treatment of catalytic reaction (1). In preparation of some supported catalysts, calcination would cause some active compounds to migrate to the surfaces of supports and to become high dispersion states (2-4). During a catalytic reaction, reactant molecules may move around on the surface of the catalyst to the active sites and react. Spillover is another interesting phenomenon related to surface migration in catalysis. It involved active species formed on the surface of one phase (activator) migrating to the surface of another phase (acceptor) (5). In order to further show the importance of surface migration or diffusion in catalysis, in this paper, we will discuss a phenomenon of spontaneous monolayer dispersion.