Monometallic Pd/C and Re/C and bimetallic Pd−Re/C catalysts with different Re/Pd molar ratios were prepared by incipient-wetness impregnation and characterized by temperature-programmed reduction, X-ray diffraction, CO chemisorption, and transmission electron microscopy. The results indicated that there is a strong interaction between Pd and Re species and that Pd can significantly promote the reduction of rhenium oxide. The hydrogenation of succinic acid to γbutyrolactone and tetrahydrofuran was investigated over the as-prepared Pd/C, Re/C, and Pd−Re/C catalysts. Pd/C showed a low conversion of succinic acid and a high selectivity to γ-butyrolactone. Adding a small amount of Re evidently enhanced the hydrogenation activity of succinic acid and improved the yield of γ-butyrolactone, whereas more Re increased the yield of tetrahydrofuran. The main reaction pathway for the conversion of succinic acid in aqueous solution on Pd−Re/C catalysts is proposed through hydrogenation of the intermediates, including γ-butyrolactone, 1,4-butanediol, and tetrahydrofuran as the substrates.

No abstract

Interstitial silicide-modified nickel, with high selectivity in some hydrogenation reactions, had been produced by dissolving silicon atoms into the nickel lattices. The metallic nickel was obtained by reducing the as-prepared high surface area NiO, followed by modification of the bulk nickel through silification of silane/H2 at relatively low temperature and atmospheric pressure. The as-prepared materials were characterized by X-ray diffraction, magnetic measurements, X-ray photoelectron spectroscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, and temperature-programmed reduction. The results show nickel silicide formation involves the following sequence as a function of increasing temperature: Ni (cubic) → Ni2Si (orthorhombic) → NiSi (orthorhombic) → NiSi2 (cubic). The insertion of Si atoms into the interstitial sites between Ni atoms resulted in a significant change in the unit cell lattice of nickel. All of the silicide-modified nickel materials were ferromagnetic at room temperature, and saturation magnetization values drastically decreased when Si is present. Silicide-modified nickel develops a thin silicon oxide layer during exposure to air, which can be removed by H2-temperature programmed reduction. The as-prepared bulk silicide-modified nickel showed above 92% styrene selectivity in the hydrogenation of phenylacetylene under 0.41 MPa H2 and at 50 °C for 5 h. In addition, only low conversions were obtained for styrene hydrogenation under the same hydrogen pressure and temperature for 50 min. These results indicate that these novel silicide-modified nickels are promising catalysts for the selective hydrogenation of unsaturated hydrocarbons.