Acidic properties of nickel sulfate supported on TiO_2-ZrO_2 and catalytic activity for acid catalysis

摘要

A series of catalysts,NiSO_4/TiO_2-ZrO_2,was prepared by the impregnation method using an aqueous solution of nickel sulfate.Calcination at 300-600 deg C of co-precipitated Ti(OH)_4-Zr(OH)_4 resulted in the formation of an amorphous phase and further heating at 700 deg C and above resulted in the formation of crystalline ZrTiO_4 compound.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 ZrTiO_4 from amorphous to orthorhombic to higher temperature because of the interaction between nickel sulfate and ZrTiO_4,and the acid amount of NiSO_4/TiO_2-ZrO_2 increased in proportion to the nickel sulfate content up to 20 wt.% of NiSO_4.The high catalytic activity of NiSO_4/TiO_2-ZrO_2 was related to the increases of acid amount and acid strength due to the addition of NiSO_4.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 NiSO_4/TiO_2-ZrO_2 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.