Homogeneous Surface Ionization Models

Let us now concentrate our attention on the surface of the support grains, more precisely on the surface of the support nanoparticles that constitute the grains. In spite of the progress with respect to the surface structure of the oxidic supports thanks to crystallography or IR spectroscopy, rather hypothetical homogeneous surface ionization (or surface binding or surface complexation) models have been used to describe their protonation/deprotonation behavior in aqueous solutions. 

According to the most familiar one-site/two-pK model [14] only one generic kind of oxo-/hydroxo-groups is developed on the surface of an oxide in contact with water. Depending on the pH of the impregnating solution these groups may be protonated/deprotonated. 

Only one generic kind of surface of oxo-/hydroxo-groups is also assumed in the context of the one-site/one-pK model [15-17]. 

In the above equilibria by Hs we denote the hydrogen ions located near to the surface. According to the first model, the surface oxygens, with an arbitrary 

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