ETHYLENE HYDROGENATION OVER LANTHANIDE-DOPED CU AND AG CATALYST SYSTEMS (EU-CU, YB-CU, EU-AG AND YB-AG)

Metal powders (Cu and Ag) react readily with Eu and Yb which dissolve in liquid ammonia, resulting in the formation of active lanthanide-doped catalysts (Eu-Cu, Yb-Cu, Eu-Ag and Yb-Ag). The catalytic properties of the samples with varied levels of lanthanide doping have been evaluated in the hydrogenation of ethylene. For Eu-Cu and Yb-Cu the hydrogenation activity increased rapidly with the lanthanide addition and then gradually; increases of over three or four orders of magnitude compared with the constituent metals alone were observed. The activity of Eu-containing systems was, in most cases, higher than that of the Yb-containing systems. The catalytic behaviour was markedly dependent on the evacuation temperatures of the catalysts before reaction. This is due to the reconstruction of surface morphology with an increase in the pretreatment temperature, which brings about the interaction between the lanthanide and transition metals to form active sites synergistically. This phenomenon is most probably associated with appearance of high catalytic activity for the present systems. The nature of the active sites formed and the effect of lanthanide addition are discussed.