The Mechanisms of Chemical Reactions on Surfaces

Who durst be so bold with a few crooked boards nailed together, a stick standing upright, and a rag tied to it, to adventure into the ocean 

Another characteristic of catalytic reactions is that it cannot in general be assumed, once reaction is established at a certain rate under given conditions, that the rate will remain constant with the passage of chronological time. Catalysts normally lose some or all of their specific activity for a desired chemical transformation with time of utilization. This effect, normally referred to as deactivation, can come from a number of different sources and is often very important in the analysis and/or design of catalytic processes and reactors. 

Our concern also includes reactions that are catalyzed by enzymes, and we will have the opportunity to see the parallel development of the topics of chemical catalysis and enzyme catalysis as set forth by two related scientific communities (physical chemistry and biochemistry) with little apparent intercommunication but with essentially the same results. 

It is most convenient to consider surface reactions as a series of several steps, in essence a type of chain reaction, which (as we have seen in Chapter 1) employs the active centers of reaction in a closed sequence. Let us again turn to the simple example of an isomerization reaction, A B, now taking place on a surface containing one type of active center, S. The individual reaction steps are  

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