Isoprene hydrogenation was investigated on Pd-Fe/alumina catalysts in the liquid phase. Iron added by a controlled surface reaction (CSR) promotes the activity of small palladium particles while the opposite effect is generally observed on catalysts prepared by coimpregnation or successive impregnations of the metal precursor salts. Iron introduced by CSR would be deposited on the surface of palladium particles while the other preparation techniques would lead to alloy formation,