Promoting effect of Al 2O 3 on catalytic activity of NiSO 4/ZrO 2 for ethylene dimerization

Abstract

The NiSO 4/Al 2O 3–ZrO 2 catalysts containing different nickel sulfate and Al 2O 3 contents were prepared by the impregnation method. Here the support, Al 2O 3–ZrO 2, 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 Al 2O 3–ZrO 2. The addition of nickel sulfate (or Al 2O 3) to ZrO 2 shifted the phase transition of ZrO 2 (from amorphous to tetragonal) to higher temperatures because of the interaction between nickel sulfate (or Al 2O 3) and ZrO 2. 10-NiSO 4/5-Al 2O 3–ZrO 2 containing 10 wt.% NiSO 4 and 5 mol% Al 2O 3, and calcined at 700 °C exhibited a maximum catalytic activity for ethylene dimerization. NiSO 4/Al 2O 3–ZrO 2 catalysts was very effective for ethylene dimerization even at room temperature, but Al 2O 3–ZrO 2 without NiSO 4 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 Al 2O 3 up to 5 mol% enhanced the acidity, surface area, thermal property, and catalytic activities of catalysts gradually, due to the interaction between Al 2O 3 and ZrO 2 and due to consequent formation of Al O Zr bond.