The hydrogenation of citral over a series of supported iridium catalysts was investigated. The nature of the support (TiO2 and SiO2), the effect of additives (Fe and Ge), and the influence of the reduction temperature on catalyst performance have been examined. It was found that the presence of ionic species, such as, promoters or species generated upon reduction at high temperature of the reducible TiO2 Support, i.e. TiOx moieties, leads to catalysts active and highly selective to the hydrogenation of the carbonyl bond. This is explained in terms of the presence of positively charged (Fe3+, Ge4+) species in intimate contact with Ir, which are responsible for the polarisation of the C=O bond. (C) 2002 Elsevier Science B.V. All rights reserved.