Pt-Ir/Al2O3 catalysts were modified by addition of an inactive metal, germanium, in order to suppress the strong hydrogenolytic activity of this type of naphtha reforming catalyst. The trimetallic systems were prepared by a surface redox reaction called catalytic reduction method. The objective of the study is to examine the influence of the Ge addition step and of the activation step (calcination-reduction or only reduction) of these systems on their catalytic properties. The Pt-Ir metallic function deposited on alumina does not suffer a significant sintering of the particles neither during the catalytic reduction procedure (i.e. an immersion in acidic medium under hydrogen flow) nor during the final activation step. On the other hand, an inhibition of the acidic function of the bimetallic parent catalysts is observed after the catalytic reduction treatment. Ge affects both the metal and the acidic functions of the Pt-Ir-Ge trimetallic catalysts, the effects depending on the deposited Ge content and on the activation treatment. The best catalytic properties are obtained for the Pt-Ir-Ge/Al2O3 catalyst with the lowest Ge content (0.1 wt%) and directly reduced. (C) 2007 Elsevier B.V. All rights reserved.