Promoting effect of Al2O3 on catalytic activity of NiSO4/ZrO2 for ethylene dimerization

The NiSO4/Al2O3-ZrO2 catalysts containing different nickel sulfate and Al2O3 contents were prepared by the impregnation method. Here the support, Al2O3-ZrO2, was prepared by the coprecipitation method using a mixed aqueous solution of zirconium oxychloride and aluminum nitrate solution followed by adding an aqueous ammonia solution. No diffraction line of nickel sulfate was observed up to 20 wt.%, indicating good dispersion of nickel sulfate on the surface of Al2O3-ZrO2. The addition of nickel sulfate (or Al2O3) to ZrO2 shifted the phase transition of ZrO2 (from amorphous to tetragonal) to higher temperatures because of the interaction between nickel sulfate (or Al2O3) and ZrO2. 10-NiSO4/5-Al2O3-ZrO2 containing 10 wt.% NiSO4 and 5 mol% Al2O3, and calcined at 700 °C exhibited a maximum catalytic activity for ethylene dimerization. NiSO4/Al2O3-ZrO2 catalysts was very effective for ethylene dimerization even at room temperature, but Al2O3-ZrO2 without NiSO4 did not exhibit any catalytic activity at all. The catalytic activities were correlated with the acidity of catalysts measured by the ammonia chemisorption method. The addition of Al2O3 up to 5 mol% enhanced the acidity, surface area, thermal property, and catalytic activities of catalysts gradually, due to the interaction between Al2O3 and ZrO2 and due to consequent formation of AlOZr bond.