Effects of lanthanide metals in Eu–Ni and Yb–Ni bimetallic catalysts

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Abstract
Lanthanide metals (Eu and Yb) dissolved in liquid ammonia and reacted readily with reduced Ni powders to form Eu–Ni and Yb–Ni bimetallic catalysts with different lanthanide contents. The catalysts were characterized by the hydrogenolysis of ethane and cyclohexane, the hydrogenation of ethene, hydrogen chemisorption and temperature-programmed desorption (TPD) measurements. The rate of hydrogenolysis decreased markedly when Yb and Eu were added to the Ni surface, whereas the hydrogenation activity showed a tendency to increase, especially in the Eu–Ni system. The lanthanide itself showed a low activity for the hydrogenolysis and hydrogenation reactions under the reaction conditions. An analysis of the decrease in the rate of hydrogenolysis with lanthanide addition suggested a decrease in concentration of surface nickel available for structure-sensitive reactions caused by lanthanide coverage. For the hydrogenation of ethene the surface was gradually covered with the lanthanide metals and simultaneously certain interactions occurred to produce active centres; the presence of lanthanide metals on Ni strongly influenced the state of adsorption of hydrogen in the subsequent activation processes, resulting in enhanced capacity of this surface to dissociate hydrogen. For the hydrogenation of ethene and adsorption characteristics, lanthanide and transition metals were more efficient when they were used together.