Selectivity in ethylene dimerization over supported nickel oxide catalysts

Abstract

Ethylene dimerization was carried out over nickel oxide catalysts supported on various carriers. Only catalysts supported on acidic silica and/or alumina exhibited activity for ethylene dimerization and for but-1-ene isomerization. The higher activity of the silica-containing catalysts as compared with the alumina containing catalysts, is attributable to the number of active sites. Alumina supported catalysts conferred an induction period on the reaction. With ethylene dimerization in pulse reactors the induction period was also found; here it was ascribed to the formation of active centres by adsorption of ethylene. NiO catalysts supported on SiO₂–Al₂O₃ produced both but-1-and-2-enes at an early stage of the dimerization, whereas the other catalysts produced only but-1-ene, followed by rapid isomerization to but-2-ene, because the rate of the isomerization of but-1-ene was higher than that of the ethylene dimerization. The infrared spectra of pyridine adsorbed on the NiO-SiO₂-Al₂O₃ catalyst showed both Brönsted and Lewis acid sites whereas the other catalysts has only Lewis acid sites. Accordingly the Brönsted acid site seems to provide a direct path from ethylene to but-2-ene.