Lanthanide (Eu or Yb)-promoted Ni, Cu and Ag-catalyzed transfer hydrogenation with NH3 as a hydrogen donor

Novel lanthanide (Ln)-promoted Ni, Cu and Ag catalysts prepared by the reac tion of Ni/SiO2, Cu/SiO2 and Ag/ZrO2 with the dissolved Eu ol Yb metals in liquid ammonia have been studied for the catalytic transfer hydrogenation o f ethene, buta-1,3-diene and propyne. The transfer hydrogenation with the a id of ammonia as a hydrogen donor was greatly enhanced by the Ln-promoted c atalysts. The catalytic activity for the transfer hydrogenation increased w ith increasing lanthanide content in the bimetallic catalysts, which eviden tly reflected synergetic effects between the lanthanide and transition meta ls. The transfer hydrogenation of ethene with ammonia over Eu-Ni/SiO2 proce eded to form ethane and nitrogen, maintaining the following stoichiometric relationships: 3C(2)H(4) + 2NH(3) --> 3C(2)H(6) + N-2 The catalytic hydroge n transfer from ammonia to buta-1,3-diene or propyne similarly followed the stoichiometric relationships. The Ln-promoted catalysts showed substrate s electivity for the transfer hydrogenation using ammonia as the hydrogen sou rce; Ln-Ni/SiO2 was reactive for ethene and buta-1,3-diene, but not for pro pyne. Ln-Cu/SiO2 was active for propyne and buta-1,3-diene. Ln-Ag/SiO2 was relatively active for buta-1,3-diene. The major factors governing the catal ytic 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 m olecules occurs concertedly. (C) 1999 Elsevier Science B.V. All rights rese rved.