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A series of catalysts, NiSO 4 /TiO 2 -ZrO 2 , for ethylene dimerization was prepared by the impregnation method using an aqueous solution of nickel sulfate. For NiSO 4 /TiO 2 -ZrO 2 sample, no diffraction line of nickel sulfate was observed up to 30 wt%, indicating good dispersion of nickel sulfate on the surface of TiO 2 -ZrO 2 . The addition of nickel sulfate to TiO 2 -ZrO 2 shifted the phase transition of TiZrO 4 from amorphous to orthorhombic to a higher temperature because of the interaction between nickel sulfate and TiO 2 -ZrO 2 . The number of acid sites of NiSO 4 /TiO 2 -ZrO 2 increased in proportion to the nickel sulfate content up to 20 wt% of NiSO 4 . Nickel sulfate supported on TiO 2 -ZrO 2 was found to be very active even at room temperature, giving a maximum in both activity and acidity, when the catalyst containing 20% NiSO 4 was calcined and evacuated at 500°C. The asymmetric stretching frequency of the S @ O bonds for NiSO 4 /TiO 2 -ZrO 2 samples was related to the acidic properties and catalytic activity. That is, the higher the frequency, the higher both the number of acid sites and the catalytic activity for ethylene dimerization.