INDEX isosteres

The lack of correlation between isosteric heats of adsorption and catalytic activity illustrates the point we have been stressing the strength of attachment of a base to a catalyst surface is not a valid index of catalytic activity when a substantial portion of the base is strongly bonded to inactive portions of a catalyst surface. Putting it more explicitly, isosteric heats of adsorption are useful indexes for the prediction of acid-catalyzed... 

In this context the isosteric heat of adsorption approaching zero coverage Qo = Qiso 9 0) is another important quantity. Its experimental determination is more delicate and may be obscured by the fact that the initial adsorption may preferentially occur at surface defects (steps) or impurities due to a stronger binding of the noble gas atoms to these defects. In fact, the increase of Qi at very low coverage observed, e.g., on stepped or high index snrfaces allows to extract the adsorption energy of the defect sites and can even be used as a quantitative measure to determine the defeet concentration. 

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