who concluded that the activity of a catalyst is given by the binding energy to adsorbed species, and that there is an optimum in binding energy for the most active catalyst. This results in lower activities for lower or higher binding energies, the so-called Volcano plots. An early example for such kind of correlation was given by Trasatti for the electrocatalytic hydrogen evolution reaction, where a plot of exchange current density on a large number of metal electrodes versus the metal-H bond strength resulted in an essentially perfect volcano. Similar correlations were later reported also between d-band occupancy and ammonia synthesis activity or the activity in the hydrogenolysis of C-X bonds (X=C, N, Cl) .