The enantioselective hydrogenation of 1-phenyl-1,2-propanedione at 298 K and 40 bar over modified iridium-supported catalysts has been studied, using cinchonidine as modifier. The catalysts were prepared by impregnation of Ir(acac)3 on two different supports: SiO2 and TiO2, followed by calcination in air and reduction under hydrogen flow at 773 K. The effects produced by the reduction temperature (473 and 773 K) and the effect of the addition of promoters (CeO2 and MoO3) on catalyst surface properties were studied in Ir/TiO2 catalysts. All the samples were characterized by nitrogen adsorption-desorption isotherms at 77 K, H-2 chemisorption, XRD, TEM, XRD and XPS. In some cases, there was an enhancement in the reaction rate when Irdelta+ species were in the catalysts. The effect of the chiral modifier concentration was also studied and the results revealed a bell-type curve dependence of the enantiomeric excess with the modifier concentration. (c) 2005 Elsevier B.V. All rights reserved.