Provided that some assumptions are made on chemisorption stoichiometric factor (H/MS) and the nature of atomic planes exposed on the surface, the particle size (d(nm)) and the metallic specific surface area (SM) of noble fcc metals catalysts can be obtained . The common assumption is that the values of H/MS = 1 for Pt, Pd, Ir, and Rh metals . However, some data also report H/MS stoichiometry factor exceeding unity for Pt, Pd, Rh, and Ir supported catalysts. For instance, data compiled by Bartholomew show chemisorption stoichiometric factor (H/MS) values of 1.0–1.2 for Pt, Pd, Rh, and Ir catalysts  Kip et al. performed careful characterization of supported platinum, rhodium, and iridium catalysts by hydrogen chemisorption and EXAFS data analysis. They reported H/M ratios exceeding unity for Pt (H/Pt = 1.14) and Rh (H/Rh = 1.98), and even higher than 2 for Ir (H/Ir = 2.68) over highly dispersed metal catalysts supported on Al2O3 and SiO2 . McVicker et al. reported a H/Ir ratio close to 2 for small particle sizes (<0.6 nm) over highly dispersed Ir catalysts on Al2O3 . Krishnamurthy et al. have shown that 0.48 wt% Ir/Al2O3 catalyst adsorbed up to 2.72 hydrogen atoms per iridium atom .