Catalytic properties of Pt-Ge intermetallic compounds in the hydrogenation of 1,3-butadiene

Article abstract of DOI:10.1021/jp971117l

Catalytic properties of Pt-Ge intermetallic compounds, Pt₃Ge, Pt₂Ge, and PtGe, were studied for the H₂-D₂ equilibration and the hydrogenation of 1,3-butadiene. Powdered Pt, Ge, and the Pt-Ge intermetallic compounds were treated with H₂ at 873 K to reduce their surface oxidized in air. XPS spectra measured after the H₂ treatment showed the complete reduction into Pt⁰ and Ge⁰ and the stoichiometric surface composition for all the intermetallic compounds. The valence band XPS spectra suggested the electron transfer from Ge into Pt, which was also evidenced by the positive shift in the Ge3d XPS spectra. The activity of the intermetallic compounds for H₂-D₂ equilibration was much lower than that of pure Pt. Their low activity for the hydrogen dissociation resulted in the low activity for the hydrogenation of 1,3-butadiene. On the intermetallic compounds, no butane was formed at the initial stage of the reaction. After most of 1,3-butadiene was converted into butenes, the secondary hydrogenation of butenes into butane took place very slowly because of their intrinsically low activity for the hydrogenation of butenes. The hydrogenation with a mixture of H₂ and D₂ showed no inhibiting effect of 1,3-butadiene and 1-butene on the H₂-D₂ equilibration. Kinetic studies on the hydrogenation over Pt₃Ge revealed that the reaction rate was zero-order with respect to the partial pressure of hydrogen and first-order to that of 1,3-butadiene or 1-butene. The rate-determining step in the hydrogenation of 1,3-butadiene would be the adsorption of 1,3-butadiene. The strength of the adsorption was in the order of H₂ a?? 1,3-butadiene > 1-butene on Pt₃Ge. The weaker adsorption of butenes would result in the high selectivity to butenes in the hydrogenation of 1,3-butadiene.