Iridium supported catalysts prepared by the sol-gel and impregnation methods have been studied in the vapour-phase hydrogenation of crotonaldehyde. The influence of different preparation variables on the surface and catalytic properties was analysed. It was found that the porosity of the support has an effect on the selectivity to the unsaturated alcohol and the presence of partially reducible supports such as ZrO2 and TiO2 increases the selectivity to crotyl alcohol. This increase may be attributed to an enhancement of the polarisation of the C=O bond as a result of surface decoration of the metal component. The presence of chlorine ions in the metal-support interfacial region also allows, in a certain extension, a polarisation of the carbonyl bond. The effect of the reaction temperature has also been studied. It was found that a decrease in the reaction temperature led to a decrease in the crotonaldehyde conversion and in an improvement on the selectivity of the allylic alcohol.