Adsorption on Surfaces Modified by Electropositive or Electronegative Promoters

5 ADSORPTION ON SURFACES MODIFIED BY ELECTROPOSITIVE OR ELECTRONEGATIVE PROMOTERS 

The key of the promotional action is the effect of electropositive and electronegative promoters on the chemisorptive bond of the reactants, intermediates and, sometimes, products of catalytic reactions. Despite the polymorphic and frequently complex nature of this effect, there are two simple rules always obeyed which can guide us in the phenomenological survey which follows in this chapter. 

Rule 1 Electropositive (electron donor) promoters enhance the chemisorption of electron acceptor adsorbates and weaken the chemisorption of electron donor adsorbates. 

The rules are simple as long as we also keep site-blocking effects in mind and as long as we can identify the electron acceptor or electron donor character of the various adsorbates. 

---