Catalytic Kinetics and Promoters

Despite the already discussed oversimplifications built into the Langmuir isotherm and in the resulting LHHW kinetics, it is useful and instructive at this point to examine how a promoter can affect the catalytic kinetics described by the LHHW expressions (2.11) to (2.14). 

A promoter is, first of all, just another adsorbate on the catalyst surface. In a Langmuirian context it blocks sites. Thus if its coverage on the catalyst surface is 0P, the simplest LHHW rate expression (2.14) becomes  

Such an expression is sometimes found to provide an adequate description of catalyst poisoning, i.e. the reverse of promotion. But for a promoter, i.e. a coadsorbate which enhances r, it is clear that at least one of the following two events must happen  

It therefore becomes important first to examine the chemisorption of promoters on clean catalyst surfaces and then to examine how the presence of promoters affects the chemisorptive bond of catalytic reactants. 

4 INTERACTIONS OF ADSORBATES ACTING AS PROMOTERS OR POISONS WITH CATALYST SURFACES 

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