Metallic catalysts are involved in 80% of the industrial catalytic processes . These catalysts are of great importance in various fields, such as synthesis chemistry, energy production, but also, environment processes . Among all transition metals, noble metals (or platinum group metals), such as Pd, Ir, and Rh, are of particular interest as catalysts for large scale industrial applications. A non-exhaustive list of applications for Pd include hydrogenation  or Suzuki cross-coupling reactions . Rh is commonly used in the preparation of catalysts for the reduction of NOx in automotive applications , and hydrogen production by steam reforming . Iridium is generally used as a catalyst for propulsion applications  or ring opening reactions . In catalysis, the activity of catalysts is currently expressed in the literature by the turnover frequency (TOF), exhibiting the activity per active site. In catalysis by metals, the mean metal particle size and the dispersion are required to be known precisely, to determine the TOF.