The rates of uptake of noble metal complexes over the surfaces of porous alumina are controlled partially by pore diffusion and partially by the rate of the chemical process between the metal complex and the alumina, resulting in impregnation profiles of different shapes. The rate of removal of metal complexes by alumina from solution is inversely related to the depth to which the noble metal penetrates into the alumina pellet. For those complexes that are rapidly removed from solution, the noble metal profile resembles a sharp shallow band, located at the pellet's outer edge. On the other hand, for those complexes that are slowly removed from solution, the noble metal profiles in the pellets are essentially uniform along the radius of the catalyst pellets. Anionic chloride complexes, e.g., MCl6n− and MCl4n−, appear to react with alumina surfaces by a ligand displacement reaction. For a series of (NH4)aMCl6 complexes, the relative reactivities toward γ-alumina are Pd > Rh > Ru ≫ Pt ∼- Ir.