Adsorption Isotherm on the Kinetics of Heterogeneous Catalysis

Influence of the Adsorption Isotherm on the Kinetics of Heterogeneous Catalysis 

The course of a surface reaction can in principle be followed directly with the use of various surface spectroscopic techniques plus equipment allowing the rapid transfer of the surface from reaction to high-vacuum conditions see Campbell [232]. More often, however, the experimental observables are the changes with time of the concentrations of reactants and products in the gas phase. The rate law in terms of surface concentrations might be called the true rate law and the one analogous to that for a homogeneous system. What is observed, however, is an apparent rate law giving the dependence of the rate on the various gas pressures. The true and the apparent rate laws can be related if one assumes that adsorption equilibrium is rapid compared to the surface reaction. 

It will be recalled (Eq. XVII-11) that is the case of competitive adsorption the Langmuir equation takes the form 

If a surface reaction is bimolecular in species A and B, the assumption is that the rate is proportional to 5a x 5b- We now proceed to apply this interpretation to a few special cases. 

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