Synthesis Of TiO₂-Al₂O₃ And Catalytic Performance Of Its Supported NiMo For HDS Of Dibenzothiophene

With the continuous improvement of the quality requirements of gasoline and diesel in environmental protection regulations,the heavier and inferior quality of crude oil continues to increase,and the content of sulfur and nitrogen in oil products continues to increase,which puts forward higher requirements for hydrodesulfurization catalysts.The traditional alumina support has too strong metal-supports interactions,and its activity and anti-toxicity need to be improved.The TiO₂-Al₂O₃ composite support can combine the advantages of TiO₂ and Al₂O₃,and has a broad development prospect.In this paper,TiO₂-Al₂O₃ composite support was prepared by coprecipitation method with PEG as template.Under the optimized preparation conditions,when the reaction temperature is 70℃,the amount of PEG is 60 g/L,and the concentration of reactants(Ti⁴⁺+Al³⁺)is 0.50 mol/L,the composite support has a large specific surface area and excellent pore structure,which provides a material basis for the preparation of high-performance hydrodesulfurization catalysts.Then a series of TiO₂-Al₂O₃ composite supports and catalysts with different titanium aluminum ratio were prepared.The composite supports were characterized by XRD,BET,NH₃-TPD,Py-FTIR,SEM and EDS.It was found that the TiO₂-Al₂O₃ composite support with TiO₂/Al₂O₃ mole ratio of1:1 is more uniform,and the pore structure is the best.All TiO₂-Al₂O₃ composite supports only have Lewis acid sites,no Br（?）nsted acid sites,and the acidity is moderate.The catalysts were characterized by XPS and HRTEM.It was found that compared with alumina catalyst,the active metal sulfidation degree on the composite support catalyst was higher,and the average stacking number and length of Mo S₂ slabs were increased.Taking DBT as the model compound,it is found that the hydrodesulfurization performance of composite support is the best when the TiO₂/Al₂O₃ mole ratio is 1:1.Compared with alumina catalyst,the HYD/HDS ratio of composite support catalyst is higher.The effect of calcination temperature on the properties of the composite support with TiO₂/Al₂O₃ mole ratio of 1:1 was investigated.The composite support was characterized by XRD,BET,NH₃-TPD,SEM and EDS.It was found that the calcination temperature has a great influence on the physical and chemical properties of the composite support,and the surface grains of the composite support were agglomerated at 650℃.The catalysts were characterized by XPS and HRTEM.It was found that with the increase of calcination temperature,the interaction between active metal components and support decreased,the average stacking number and length of Mo S₂ slabs were increased.When the calcination temperature is 550℃,the hydrodesulfurization performance of the catalyst is the best.In order to further improve the hydrogenation activity of the catalyst,the effects of different content of citric acid modification on the properties of the catalyst were investigated.It was found that after adding different content of citric acid,the sulfurization degree of Mo and Ni on the catalyst increased,especially the proportion of Ni Mo S active phase increased significantly,with the increase of citric acid content,The average stacking number of Mo S₂ slabs on each catalyst increases gradually,and the length of the slabs decrease gradually.The hydrodesulfurization performance of the catalyst modified with different content of citric acid is improved,and the proportion of HYD path is increased.When the molar ratio of citric acid to Ni is 1.5,the hydrodesulfurization performance of the catalyst is the best.