Is there a direct relationship between the adsorption energy and the catalytic activty

Question

I have seen in several papers, where people correlate adsorption energy with the catalytic activity; the greater the adsorption energy, the greater would be the catalytic activity.

I understand that in order for a catalytic reaction to take place, the adsorbates should get adsorbed on the surface of the catalyst. But what if the adsorbates are too strongly adsorbed on the catalyst. This is unfavorable for the reaction. Isn't it?

Therefore, I don't understand how one can correlate higher adsorption energies with greater catalytic activity.

Answer 1

Adsorption energy is indeed related to catalytic activity, but not "greater energy means greater activity".

As you were guessing, there is an optimum window in adsorption energies for which catalytic activity is maximum, this is explained by the Sabatier principle:

The Sabatier principle is a qualitative concept in chemical catalysis named after the French chemist Paul Sabatier. It states that the interactions between the catalyst and the substrate should be "just right"; that is, neither too strong nor too weak. If the interaction is too weak, the substrate will fail to bind to the catalyst and no reaction will take place. On the other hand, if the interaction is too strong, the product fails to dissociate.

There is a nice recent paper in which you can find much more mechanistic details.

Answer 2

The energetics of adsorption and the hydrophobicity of a surface play an important role in catlytic activity at that surface. Catalysed pathways are complex, and actually quite poorly understood mechanistically. The range of catalysed reactions is incredibly broad, and each reaction tends to be the subject of intense discussion regarding mechanistic pathways. Needless to say, to answer your question there is an indirect relationship between adsorption energy and catalytic activity. Generally you want good adsorption of reactants. However adsorption, for example of water, can be associative (molecular) or dissociative adsorption. This is of great consequence in catalytic activity. Different surfaces, owing to their surface lattice, show differing affinities for adsorbed species and thus when examining catlyst activities, it is important to consider the level at which individual planes are expressed.