Reaction mechanisms in catalysis by metals

Abstract The primary steps involved in a heterogeneously catalyzed reaction are illustrated schematically by Figure 1. These include adsorption and desorption steps of the particles involved as well as surface migration and reactive and nonreactive interactions. Thus a reaction path may be offered to the overall chemical transformation which is eventually more favorable and proceeds with a higher rate than reaction in the homogeneous phase. If a reaction of the type A + B → C is considered the rate of product formation, r = d[C]/dt will usually be expressed as f(pA, pe, pc, T). That means that kinetic measurements yield information on the dependence of the rate on the concentrations of the particles involved in the gaseous phase. Inspection of Figure 1, however, shows that the primary steps rather involve the surfoce species, whose Concentrations and even chemical nature will be quite different. From this it becomes evident that kinetic measurements alone provide only rather indirect (and often even misleading) information on the microscopic reaction mechanism.