Hydrogenation behavior of propyne on supported Eu-Pd and Yb-Pd bimetallic catalysts with anomalous hydrogen uptake

摘要

The hydrogenation of propyne over SiO_2-supported lanthanide (Ln: Eu or Yb)-palladium bimetalliccatalysts was studied at 203-273 K, especially concerning thehydrogenation behavior with considerable hydrogen uptake.Upon introduction of Eu or Yb onto Pd surfaces by the reactionof 5 mass percent Pd/SiO_2 with the lanthanide metal dissolvedin liquid ammonia, the ability of hydrogen uptake by the catalystappeared during the hydrogenation of propyne. When the mixedgases, propyne and hydrogen, were brought into contact withLn-Pd/SiO_2, considerable hydrogen uptake occurred, followedby hydrogenation to simultaneously form propene and propanePd/SiO_2-catalyzed propyne hydrogenation showed differentproduct selectivity, in which negligible hydrogen uptake wasobserved. This indicates a mechanism different from that for Ln-Pd/SiO_2. Ln-Pd/SiO_2 showed remarkable synergetic effectsbetween the lanthanide and palladium metal involvinganomalous hydrogen uptake and hydrogenation behavior. Thepresence of adsorbed propyne on the catalyst surface wasimportant to induce a promoting effect towards rapid hydrogenuptake with subsequent propyne hydrogenation. It seems quitecertain that the hydrogenation on Ln-Pd/SiO_2 predominantlyproceeds through a reaction path using hydrogen taken up by the catalyst.