Activation specific adsorptive powers, development

Such effects suggest an influence arising from the chemical properties of the catalyst. Specific catalytic effects depend on properties of the surface atoms, and these properties, in turn, are a function of the chemical nature of the catalytic substance. This is shown by the fact that the same type of active surface is not developed on copper as on platinum, and both differ from the active surface that can be formed on carbon. Properties of surface atoms that are important in catalysis appear to be linked to specific adsorptive powers, thus hydrogenating and dehydrogenating catalysts adsorb hydrogen, whereas oxidizing catalysts adsorb oxygen. 

The temperature at which certain other adsorptive powers develop often corresponds to a temperature favorable to the formation of one of the surface oxides. This, however, does not establish a direct connection between a specific adsorptive power and the surface oxide. Let us consider the adsorption of Malachite Green. For this, certain temperatures of activation are favorable but only when the carbon has been given suitable previous treatment. Moreover, adsorptive power for Malachite Green when once developed is not... 

We are far from having a clear picture of just what occurs during activation aside from the fact that the surface area is increased and a very porous structure is developed. This lack of knowledge is not surprising in view of the various methods by which an activated carbon can be produced. One is often perplexed to find a step described as necessary in one process and omitted from another. In some cases, this is because the value of a particular stage may depend upon the previous history as well as on the treatment that follows. Then, too, the value of certain steps is the fact that they confer certain specific powers that may be needed in one application and not in another. It is to be remembered that each method of activation leaves a characteristic imprint on the adsorptive powers.71 Therefore, it is not uncommon to combine several different processes to provide a diversity of properties. 

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