||Properties of Pd/SiO2 catalysts modified with titanium oxide have been studied by measuring their catalytic performance for the partial hydrogenation of 1,3-butadiene in excess amounts of 1-butene and by characterizing their surface using Fourier-transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), H2 chemisorption, and temperature programmed desorption (TPD). The Ti-modified catalysts become efficient for the selective hydrogenation when reduced at high temperatures, e.g., 500 oC. IR and chemisorption results suggest that the Pd surface is decorated with partially-reduced TiOx, which suppresses the isomerization of 1-butene to 2-butenes. XPS results indicate that the Pd surface is also modified electronically, and thereby the adsorption of 1-butene on Pd is suppressed to greater extents than that of 1,3-butadiene. It is concluded that the strong interaction between the Pd surface and partially-reduced TiOx is responsible for the improved performance of the catalyst in 1,3-butaiene hydrogenation.