CATALYTIC EFFECTS OF LANTHANIDES IN HYDROGEN-ABSORBING LANTHANIDE-CO OR NI COMPOUNDS

Lanthanide metals (Ln: Eu and Yb) were dissolved in liquid ammonia and reacted readily with Co and Ni powders to form active lanthanide-cove red Co and Ni (Ln-Co and Ln-Ni). The present systems were found to be a good probe for defining and understanding the surface properties of hydrogen-absorbing lanthanide-3d transition metal intermetallic compou nds. To evaluate the surface properties towards hydrogen, Ln-Co and Ln -Ni were characterized by the isotopic exchange reaction of H-2 and D- 2. When Eu or Yb was introduced onto the Co or Ni surface, the reactio n rates of isotopic exchange somewhat decreased in the region of low c overage with the lanthanide metals and then increased with increasing coverage. The active surface of Co and Ni powders was gradually covere d with the lanthanide metals and simultaneously the interactions betwe en the lanthanide and 3d-transition metals occurred to produce local i ntermetallic compound formation on the grain surface. This is a reason why the surfaces of lanthanide-covered Sd-transition metals are activ e for catalytic activation of hydrogen.