Selective hydrogenation of 1,3-butadiene on TiO₂-modified Pd/SiO₂ catalysts

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), H₂ 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°C. IR and chemisorption results suggest that, when the catalyst is reduced at 500 °C, the Pd surface is decorated with partially-reduced TiO_x similar to the case of TiO₂-supported catalysts, which show strong metal-support interaction (SMSI). XPS and TPD results indicate that the Pd surface is also modified electronically, in that the charge is transferred from the Ti species to Pd and the adsorption of 1-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.