CATALYTIC EFFECTS OF LANTHANIDE IN LANTHANIDE COBALT BIMETALLIC CATALYST SYSTEMS

Lanthanide metals (Ln: Eu and Yb) dissolved in liquid ammonia and reacted readily with reduced Co powders to form Eu-Co and Yb-Co bimetallic catalysts with various levels of lanthanide loading. The catalysts were characterized by the hydrogenolysis of ethane, the hydrogenation of ethene and buta-1,3-diene, and hydrogen chemisorption. The rate of hydrogenolysis decreased markedly when Yb or Eu was introduced onto the Co sur-face, whereas the hydrogenation activity showed a tendency to increase, in particular for the samples with high loadings of lanthanide. Co itself was active for the hydrogenolysis and hydrogenation under the reaction conditions, while the lanthanide metals showed negligible activity. An analysis of the decrease in the rate of hydrogenolysis with increasing lanthanide loading suggested a decrease in the concentration of surface cobalt available for structure-sensitive reactions caused by lanthanide coverage. For the hydrogenation of ethene and buta-1,3-diene the surface was gradually covered with the lanthanide metals and a considerable number of interactions occurred simultaneously to produce active centres for the hydrogenation; the presence of lanthanide metals on Co strongly influenced the state of adsorption of hydrogen in the subsequent activation processes, resulting in an enhanced capacity of this surface to dissociative hydrogen. The effects of a lanthanide metal overlayer on the selectivity for buta-1,3-diene hydrogenation on a Co metal surface are also discussed.