Palladium Gallium Intermetallic Compounds for the Selective Hydrogenation of Acetylene Part II: Surface Characterization and Catalytic Performance

The structurally well-defined intermetallic compounds PdGa and Pd3Ga7 constitute suitable catalysts for the selective hydrogenation of acetylene. The surface properties of PdGa and Pd3Ga7 were characterized by X-ray photoelectron spectroscopy, ion scattering spectroscopy and CO chemisorption. Catalytic activity, selectivity and long-term stability of PdGa and Pd3Ga7 were investigated under different acetylene hydrogenation reaction conditions, in absence and in excess of ethylene, in temperature-programmed and isothermal long-term experiments. Chemical treatment with ammonia solution – performed to remove the gallium oxide layer introduced during the milling procedure from the surface of the intermetallic compounds – yielded a significant increase in activity. Compared to Pd/Al2O3 and Pd20Ag80 reference catalysts, PdGa and Pd3Ga7 exhibited a similar activity per surface area, but higher selectivity and stability. The superior catalytic properties are attributed to the isolation of active Pd sites in the crystallographic structure of PdGa and Pd3Ga7 according to the active-site isolation concept.