Catalysis by Rare Earth Metals

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In recent years there has been a growing interest in the surface properties of lanthanide-3d transition metal intermetallic compounds and lanthanide metal overlayers from the point of view of heterogeneous catalysis. It is known that Eu and Yb among lanthanide metals readily dissolve in liquid ammonia to yield homogeneous solution containing the solvated electrons. When transition metal(Co,Ni,Cu and Ag)powders are added to this solution,the metal powders react with the lanthanide metals dissolved in liquid ammonia to form specific bimetallic catalysts of layered lanthanide-transition metals. We have developed methods for the preparation of this type of novel binary compounds and have demonstrated that they can effectively catalyze various reactions.The catalysts were characterized by the hydrogenolysis of ethane,the hydrogenation of ethene and buta-1,3-diene, and the hydrogen chemisorption. The rate of hydrogenolysis decreased markedly when Yb or Eu was introduced onto the Co and Ni su … More rface,whereas the hydrogenation activity showed a tendency to increase,in particular for the samples with high loadings of lanthanide. Co and Ni were 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 concentration of surface Co or Ni 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 simultaneously considerable interactions occurred to produce active centers for the hydrogenation;the presence of lanthanide metals on Co or Ni strongly influenced the state of adsorption of hydrogen in the subsequent activation processes,resulting in enhanced capacity of this surface to dissociate hydrogen. The effects of a lanthanide metal overlayer on the selectivity for buta-1,3-diene hydrogenation on a 3d transition metal surface were also discussed. Less