Catalytic effects of lanthanides in hydrogen-absorbing lanthanide-Co or Ni compounds

Abstract

Lanthanide metals (Ln: Eu and Yb) were dissolved in liquid ammonia and reacted readily with Co and Ni powders to form active lanthanide-covered 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 compounds. To evaluate the surface properties towards hydrogen, Ln-Co and Ln-Ni were characterized by the isotopic exchange reaction of H2 and D2. When Eu or Yb was introduced onto the Co or Ni surface, the reaction rates of isotopic exchange somewhat decreased in the region of low coverage with the lanthanide metals and then increased with increasing coverage. The active surface of Co and Ni powders was gradually covered with the lanthanide metals and simultaneously the interactions between the lanthanide and 3d-transition metals occurred to produce local intermetallic compound formation on the grain surface. This is a reason why the surfaces of lanthanide-covered 3d-transition metals are active for catalytic activation of hydrogen.