Synthesis and Catalytic Properties for Phenylacetylene Hydrogenation of Silicide Modified Nickel Catalysts

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/H-2 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 suicide 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 H-2-temperature programmed reduction. The as-prepared bulk silicide-modified nickel showed above 92% styrene selectivity in the hydrogenation of phenylacetylene under 0.41 MPa H-2 and at 50 degrees 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.