The rate of adsorption of species A onto a solid surface,
is given by
After a reactant has been adsorbed onto the surface, i.e., A · S, it is capable of reacting in a number of ways to form the reaction product. Three of these ways are:
The pentane isomerization can be written in generic form as
Each step in the reaction mechanism is elementary, so the surface reaction rate law is
where KS is the surface reaction equilibrium constant KS = kS/k–S
For example, adsorbed A may react with an adjacent vacant site to yield a vacant site and a site on which the product is adsorbed, or as in the case of the dehydration of butanol, the products may adsorb on two adjacent sites.
the corresponding surface reaction rate law is
A second dual-site mechanism is the reaction between two adsorbed species, such as the reaction of CO with O.
For the generic reaction
the corresponding surface reaction rate law is
A third dual-site mechanism is the reaction of two species adsorbed on different types of sites S and S′, such as the reaction of CO with O.
For the generic reaction
the corresponding surface reaction rate law is
Reactions involving either single- or dual-site mechanisms, which were described earlier, are sometimes referred to as following Langmuir–Hinshelwood kinetics.
For the generic reaction
the corresponding surface reaction rate law is
This type of mechanism is referred to as an Eley–Rideal mechanism.
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