The Reactivity of Different Metal Surfaces

We discuss in this section the relation between type of adsorbate bond activated and its dependence on surface structure. In heterogeneous catalysis, this has important consequences for the particle size and shape dependence of catalytic reactions, where the rate is controlled by a particular bond activation reaction. 

This subsection begins with a short summary of particle-size-dependence observations of chemical bond activation. Next, the Bronsted-Evans-Polanyi relation that relates activation energies of elementary surface reaction steps with the corresponding reaction energies is introduced. In the subsections that follow, the 

It will appear that the particle size dependence of chemical bond activation distinguishes two reaction categories reactions in which the activation of a bonds is rate controUing versus reactions in which activation of molecular K bonds is rate determining. 

The chemistry of a bond activation is quite different from that of the activation of K bonds. This is summarized in brief here. Then, we discuss its consequences for particle size dependence. 

Activation of o-type CH bonds as in an alkane is the prototype of a reaction where the reaction center is a single (surface) metal atom. This in contrast to the activation of a Ji bond as in CO or N2, which requires an ensemble of surface atoms. 

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