LANTHANIDE METAL OVERLAYERS BY DEPOSITION OF LANTHANIDE METALS DISSOLVED IN LIQUID-AMMONIA ON CO AND NI - EFFECTS OF PARTICLE SIZES OF PARENT CO AND NI METALS

Lanthanide metals (Ln = Eu and Yb) dissolved in liquid ammonia and rea cted readily with reduced Co or Ni powders to form lanthanide metal ov erlayers (Ln-Co or Ln-Ni). The surface properties of Ln-Co and Ln-Ni p repared from Co and Ni precursors with different particle sizes (15-28 nn) were characterized by the hydrogenation of propene. The hydrogena tion behaviors varied markedly with changes in metal particle sizes of the Co and Ni precursors and the lanthanide content. The hydrogenatio n activity decreased with lanthanide content, passed through a minimum and increased with increasing content. The active surfaces of parent cobalt and nickel were gradually covered with the lanthanide metals an d simultaneously synergetic interactions between the lanthanide and 3d -transition metals occurred, indicating the formation of hydrogen-abso rbing surface intermetallic phases. This synergy showed a tendency to appear in the region of higher lanthanide contents with decreasing ave rage metal sizes of the Co and Ni precursors.