Lanthanide (Eu or Yb)-promoted Ni, Cu and Ag-catalyzed transfer hydrogenation with NH 3 as a hydrogen donor

Abstract

Novel lanthanide (Ln)-promoted Ni, Cu and Ag catalysts prepared by the reaction of Ni/SiO 2, Cu/SiO 2 and Ag/ZrO 2 with the dissolved Eu or Yb metals in liquid ammonia have been studied for the catalytic transfer hydrogenation of ethene, buta-1,3-diene and propyne. The transfer hydrogenation with the aid of ammonia as a hydrogen donor was greatly enhanced by the Ln-promoted catalysts. The catalytic activity for the transfer hydrogenation increased with increasing lanthanide content in the bimetallic catalysts, which evidently reflected synergetic effects between the lanthanide and transition metals. The transfer hydrogenation of ethene with ammonia over Eu–Ni/SiO 2 proceeded to form ethane and nitrogen, maintaining the following stoichiometric relationships: 3C 2H 4+2NH 3→3C 2H 6+N 2 The catalytic hydrogen transfer from ammonia to buta-1,3-diene or propyne similarly followed the stoichiometric relationships. The Ln-promoted catalysts showed substrate selectivity for the transfer hydrogenation using ammonia as the hydrogen source; Ln–Ni/SiO 2 was reactive for ethene and buta-1,3-diene, but not for propyne. Ln–Cu/SiO 2 was active for propyne and buta-1,3-diene. Ln–Ag/SiO 2 was relatively active for buta-1,3-diene. The major factors governing the catalytic transfer hydrogenation seem to be involved in the participation of the acceptor and donor molecules in the hydrogen transfer step rather than the ease of dehydrogenation of ammonia and the processes of hydrogen addition to the acceptor. The catalytic hydrogen transfer from ammonia to acceptor molecules occurs concertedly.