The properties of Pd/SiO2 catalysts modified with titanium oxide were examined by determining their activity with respect to the partial hydrogenation of 1,3-butadiene included in an excess amount of butenes and by characterizing their surfaces using infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), H-2 chemisorption, and temperature-programmed desorption (TPD). The TiO2-modified catalysts had an improved selectivity for the conversion of 1,3-butadiene to 1-butene, particularly when the catalysts were reduced at high temperatures, e.g., 500 degreesC. IR and chemisorption results suggest that, when the catalyst is reduced at 500 degreesC, the Pd surface is decorated with partially-reduced TiOx similar to the case of TiO2-supported catalysts, which show strong metal-support interaction (SMSI). XPS and TPD results indicate that the I'd surface is also modified electronically, in that the charge is transferred from the Ti species to Pd and the adsorption of I-butene to the Pd surface becomes weaker. It can be concluded that the strong interaction between the Pd surface and partially reduced TiO2 is responsible for the improved selectivity of the catalyst for the conversion of 1,3-butadiene to 1-butene. (C) 2002 Elsevier Science B.V. All rights reserved.