ABSTRACT Lanthanide metals (Ln: Eu and Yb) dissolve in liquid ammonia and react readily with reduced transition metal powders (M: Co, Ni, Cu and Ag) to form various Ln-M bimetallic catalysts with different lanthanide content. The surface properties induced upon the introduction of lanthanide metals onto the transition metals, largely for Eu-Ni and Yb-Ni, have been studied. The lanthanide-containing bimetallic catalysts are characterised by the hydrogenolysis of ethane and cyclohexane, the hydrogenation of ethene, the dehydrogenation of cyclohexane, H2-D2 equilibrium, adsorption properties of hydrogen and temperature-programmed desorption (TPD) measurements. The rates of hydrogenolysis decrease markedly when Eu and Yb are introduced onto the Ni surface, whereas the activity of hydrogenation, isotope exchange and dehydrogenation shows a tendency to increase in the region of high lanthanide content in Ln-Ni. The lanthanide metal itself exhibits negligible activity under the reaction conditions; an analysis of the decrease in the activity upon the introduction of lanthanides suggests a decrease in concentration of surface nickel available for structure-sensitive reactions caused by lanthanide coverage. For the hydrogenation, isotope exchange and dehydrogenation the surface is gradually covered with the lanthanide metals and simultaneously certain interactions occur to produce newly active centres. The presence of lanthanide metals on Ni strongly enhances the capacity of this surface to activate the H-H and C-H bonds, which is important to determine the activity for the hydrogenation and dehydrogenation, respectively. For adsorption characteristics, the lanthanide and transition metals are used more efficiently when combined.
Buy this Article
|