Synchronization of Reaction Centers

The cyclic nature of the catalytic reaction usually does not typically lead to an overall cyclic time dependence or synchronization of the reaction system. Rarely is there a synchronization of the cycle reaction phases on different reaction centers. As long as the reaction conditions are close to the equilibrium condition of a system, stationary kinetics tend to rule. However, for particular systems, when reactions are performed far from their equilibrium complex oscillations in time and even spatial organization may occur. The necessary conditions for the occurrence of cooperative time dependent and spatial events 

Spatial or temporal self organization effects have been observed on heterogeneous transition metals as well as oxide catalysts. We will illustrate here in detail these concepts using the CO oxidation reaction as an example. We briefly referred to self organizing catalytic systems earlier in Chapters 2 and 4. 

Autocatalysis is strictly defined as a reaction in which the product enhances the rate of the reaction, as, for instance, in the following reaction scheme  

In this autocatalytic reaction scheme, B is replicated by its reaction with A. Autocatalysis is therefore an elementary form of replication, a topic we will discuss extensively in the next chapter. 

The autocatalytic elementary reaction step for CO oxidation is the removal reaction of CO from the catalyst surface. The presence of adsorbed CO suppresses the dissociative adsorption of O2, because vacant surface sites are required to accommodate the oxygen atoms that are generated by dissociated molecular oxygen. The CO2 removal reaction, on the other hand, is actually autocatalytic in vacant sites since a molecule of oxygen can ultimately remove two adsorbed CO molecules, thus freeing up two additional sites. 

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