Preparation and Characterization of NiO/CeO_2-ZrO_2/WO_3 Catalyst for Ethylene Dimerization:Effect of CeO_2 Doping and WO_3 Modifying on Catalytic Activity

摘要

A series of catalysts,NiO/CeO_2-ZrO_2/WO_3,for ethylene dimerization was prepared by the precipitation and impregnation methods.For NiO/CeO_2-ZrO_2/WO_3 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 WO_3 up to the calcination temperature of 500 deg C were observed,whereas the hexagonal phase of WO_3 completely was transformed into monoclinic phase of WO_3 at 600 deg C and above.The role of CeO_2 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-CeO_2-ZrO_2/15-WO3 containing 25 wt% NiO,15 wt% WO_3 and 5 mol% CeO_2,and calcined at 400 deg C exhibited a maximum catalytic activity due to the effects of WO_3 modifying and CeO_2 doping.