Catalytic Kinetics in Presence of a Double Layer

So far we have established that the modified electrochemical Langmuir or effective double layer isotherm (Eq. 6.41) 

The crucial task remains of examining to what extent it can also describe the effect of promotion, electrochemical or classical, on catalytic reaction kinetics. More specifically we will examine to what extent it can predict the four main types of global r vs O dependence and all the associated local and global electrochemical and chemical promotional rules. 

We thus consider an arbitrary catalytic reaction between an electron donor D (X,D 0) and an electron acceptor A (Aa 0)  

We also assume that adsorbed D and A are in equilibrium with gaseous D and A respectively (pD(g) = Po(ad), pA(g) = pA(ad)) and that product adsorption is relatively weak and their desorption fast, so that the reaction between adsorbed D and A is rate limiting. 

We start by noting that when D and A coadsorb, their adsorption isotherms are given by  

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