The principle of this technique is to quantify the amount of hydrogen atoms chemisorbed on an atom located on the metal surface (MS) according to the following reaction (R1): (R1)MS+αH2→MS(H)2α where 2α represents the chemisorption stoichiometric factor of H atoms chemisorbed over the number of metal atoms located on the surface of the metallic cluster, which is defined by Equation (1): (1)2α=HMS