Surface properties of cobalt intermetallic compounds and their application to catalytic reactions.

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Co-Ge, Co-Al and Co-Sn intermetallic compounds (IMC) were prepared by melting the mixture of pure metals and then they were crushed in air to obtain powder catalysts. XRD patterns showed the formation of aimed IMC.XPS spectra taken after H_2 reduction at 873 K revealed the complete reduction of surface atoms into zero valence state. In TPD spectra of adsorbed CO,Co-Ge IMC gave different desorption peak from pure Co metal. Catalytic activity for H_2-D_2 equilibration was found to be Co CoGe>CoAl>CoGe_2>CoSn Ge.Hydrogenation of acetylene was carried out on these IMC.Co metal hydrogenated acetylene into ethane, while Co IMC gave almost exclusively ethylene. Activity of these IMC for ethylene hydrogenation was much lower than that for acetylene hydrogenation, resulting in the unique selectivity for the partial hydrogenation of acetylene. H_2-D_2 equilibration was greatly retarded by the presence of acetylene or ethylene on Co-Ge IMC.The catalytic activity of Pt or Ni for hydrogen dissociation was decreased by forming IMC with Ge or Sn, respectively. Hydrogenation of 1,3-butadiene on Pt-Ge and Ni-Sn IMC gave butene isomers with high selectivity, while butane was readily produced on pure Pt or Ni. These results indicate that the formation of IMC between highly active transition element and relatively inactive typical element leads to the catalyst having high selectivity for the partial hydrogenation.