Rate Equations for Intrinsic Surface Reactions

To describe the catalytic reaction, the catalyst must be included in the catalytic cycle as a participating species. The simplest way to do so is to consider a solid catalyst as an ensemble of single active sites ( ). The transformation from to A2 can be presented as a sequence of elementary steps  

The adsorption of the reactant is herein considered as a reaction with an empty site ( ) to give an adsorbed intermediate A. All sites are considered as equivalent and each can be occupied by a single species only. 

Considering all steps as elementary reactions, expressions for the rate of each step can be obtained  

The total concentration of active sites is represented by Zj, and the fractions occupied by Aj, A2 and the fraction of vacant sites, respectively. 

In order to derive the overall rate equation of this isomerization reaction, one should know the fraction of the sites occupied by each species, and 02, which is caUed fractional surface coverage  

---