Acidic properties of nickel sulfate supported on TiO2–ZrO2 and catalytic activity for acid catalysis Original Research Article

A series of catalysts, NiSO4/TiO2-ZrO2, was prepared by the impregnation method using an aqueous solution of nickel sulfate. Calcination at 300–600 °C of co-precipitated Ti(OH)4–Zr(OH)4 resulted in the formation of an amorphous phase and further heating at 700 °C and above resulted in the formation of crystalline ZrTiO4 compound. For NiSO4/TiO2-ZrO2 sample, no diffraction line of nickel sulfate was observed up to 30 wt.%, indicating good dispersion of nickel sulfate on the surface of TiO2–ZrO2. The addition of nickel sulfate to TiO2–ZrO2 shifted the phase transition of ZrTiO4 from amorphous to orthorhombic to higher temperature because of the interaction between nickel sulfate and ZrTiO4, and the acid amount of NiSO4/TiO2-ZrO2 increased in proportion to the nickel sulfate content up to 20 wt.% of NiSO4. The high catalytic activity of NiSO4/TiO2-ZrO2 was related to the increases of acid amount and acid strength due to the addition of NiSO4. The catalytic activities for both reactions, 2-propanol dehydration and cumene dealkylation, were correlated with the acid amounts of catalysts measured by on ammonia chemisorption method. The asymmetric stretching frequency of the SO bonds for NiSO4/TiO2-ZrO2 samples was related to the acidic properties and to the catalytic activity for acid catalysis. That is, the higher the frequency, the larger the acid amount and catalytic activities for 2-propanol dehydration and cumene dealkylation.