Preparation and Characterization of NiO/CeO₂-ZrO₂/WO₃ Catalyst for Ethylene Dimerization: Effect of CeO₂ Doping and WO₃ Modifying on Catalytic Activity

摘要

A series of catalysts, NiO/CeO₂-ZrO₂/WO₃, for ethylene dimerization was prepared by the precipitation and impregnation methods. For NiO/CeO₂-ZrO₂/WO₃ sample, no diffraction line of nickel oxide was observed up to 40 wt%, indicating good dispersion of nickel oxide on the surface of catalyst. The hexagonal and monoclinic phases of WO₃ up to the calcination temperature of 500 ∑C were observed, whereas the hexagonal phase of WO₃ completely was transformed into monoclinic phase of WO₃ at 600 ∑C and above. The role of CeO₂ in the catalysts was to form a thermally stable solid solution with zirconia and consequently to give high surface area and acidity. The catalytic activities for ethylene dimerization were correlated with the acidity of catalysts measured by the ammonia chemisorption method. 25-NiO/5-CeO₂-ZrO₂/15-WO₃ containing 25 wt% NiO, 15 wt% WO₃ and 5 mol% CeO₂, and calcined at 400 ∑C exhibited a maximum catalytic activity due to the effects of WO₃ modifying and CeO₂ doping.