Catalysis by Rare Earth Metals

近年来，从多相催化的角度研究了稀土-3D过渡金属间化合物和稀土金属覆盖层的表面性质，引起了人们的广泛关注。众所周知，稀土金属中的Eu和Yb很容易溶解在液氨中，生成含有溶剂化电子的均匀溶液。当过渡金属(Co、Ni、Cu、Ag)粉末加入到该溶液中时，这些金属粉末与溶解在液氨中的镧系金属反应，形成特定的层状稀土-过渡金属双金属催化剂。我们开发了这类新型二元化合物的制备方法，并证明了它们可以有效地催化各种反应。通过乙烷的氢解、乙烯和丁二烯的加氢以及氢的化学吸附对催化剂进行了表征。当Yb或Eu引入到Co和Ni-SU-…中时，氢解速率显著降低催化剂的加氢活性有增加的趋势，特别是在稀土负载量较高的样品中。在反应条件下，Co和Ni对氢解和加氢反应具有活性，而稀土金属的氢解活性可以忽略不计。对氢解速率随稀土负载量的增加而降低的分析表明，稀土元素的覆盖导致了可用于结构敏感反应的表面Co或Ni浓度的降低。对于乙烯和丁二烯的加氢反应，表面逐渐被稀土金属覆盖，同时发生了大量的相互作用以产生加氢活性中心；在随后的活化过程中，稀土金属在Co或Ni上的存在强烈地影响了氢的吸附状态，从而提高了该表面解离氢气的能力。讨论了稀土金属覆盖层对3D过渡金属表面丁二烯加氢选择性的影响。较少

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