Interaction of Nickel Ions with Ethylene Molecules in Ethylene Dimerization over Ni-X Zeolites

The interaction of nickel ions with ethylene molecules, the valence state and the coordination state of nickel ions and the migration of cations during the ethylene dimerization reaction over NiX zeolite catalysts have been studied. It has been found that the prereduction of Ni + catalysts in hydrogen, which was shown by ESR to be accompanied by the formation of NiX ions, could not result in the elimination of an induction period in dimerization, while the pretreatment of NiX with ethylene under reaction conditions could eliminate the induction period. Accompanying the disappearance of the induction period and the begining of ethylene dimerization, a new ESR signal appeared on the ESR spectra of NiX catalysts. It is suggested that the species characterized by the new signal are probably catalytically active intermediates formed by the interaction of Ni + ions with ethylene molecules, the results of 23 NaHMR studies indicate the migration of cations among cages during the calcination and evacuation of NiX zeolites and their activation with ethylene. An activation pattern of NiX catalysts in ethylene dimerization reaction has been proposed.