Europium and ytterbium catalysts obtained by impregnation of active carbon with lanthanide metal (Eu and Yb) solutions in liquid ammonia were found to be active for the dimerization of ethene. Ethene was selectively dimerized at 423-473 K to yield butene isomers with selectivity of 10-62%. The active catalysts were characterized as lanthanide nitride formed by the thermal decomposition of its amide.