AbstractRuthenium supported catalysts were prepared by impregnation of RuCl3 · 3 H2O and K4[Ru(CN)6] · 3 H2O aqueous acetone solutions upon several acid(base)‐modified γ‐Al2O3 samples. Characterization of the catalysts was carried out by CO chemisorption and kinetics of hydrogen reduction, correlating the particle size and dispersion of the metallic phase with the previous acid modification of the γ‐Al2O3, as well as with the type of precursor and solvent used. The surface properties were also correlated with their catalytic activities for ammonia synthesis at atmospheric pressure and 583 K (N2/H2 1/3).