The influence of pretreatment conditions of Pt/TiO2 catalysts was analyzed by different techniques and changes in the textural and chemical properties correlated with the catalytic performance in citral hydrogenation. After H-2 pretreatment, the formation of two-dimensional Pt nanoparticles and oxygen vacancies favors the diffusion of Pt species into the TiO2 structure, while three-dimensional Pt crystallites are formed after He pretreatment. The coupled effect of Pt 2-D nanoparticles and oxygen vacancies strongly enhances the catalytic activity and the selective hydrogenation of citral to unsaturated alcohols by favoring the citral adsorption on the reduced surface through the terminal C=O groups in an environment rich in hydrogen provided by the highly dispersed Pt nanoparticles. These coupled metal-vacancy active sites are formed also after a combined He/H-2 pretreatment; nevertheless, the formation of three-dimensional Pt particles during the previous He treatment strongly reduce the extent of TiO2-Pt interface and consequently the surface site concentration and the catalytic activity. (C) 2015 Elsevier Inc. All rights reserved.