ABSTRACT
In order to understand the molecular processes taking place on a catalyst surface the nature of the sites promoting the reaction must be defined. While a catalyst surface is commonly considered to be of uniform composition for ease in interpreting kinetic data, it is generally accepted that the surface of a catalyst is composed of atoms having differing environments and numbers of neighboring atoms. It is necessary, however, to define more clearly the nature of the specific active sites, be they ensembles or single atoms, that are responsible for promoting specific reactions, A number of approaches to this problem have been made over the years with varying degrees of success. Some proposals have been made that attempted to relate observed catalyst activity with the mechanisms of similar reactions taking place on soluble, monatomic homogeneous catalysts so the nature of the active site could be related to the geometry of the homogeneous complex.
