| This thesis examines the application and the hydrodesulfurization(HDS)performance evaluation of nitrilotriacetic acid(NTA),cyclohexanone diamine tetra-acetic acid(CyDTA)and ethylene diamine tetra-acetic acid(EDTA).This thesis also examines the promoting mechanism of the three kinds of nitrogen-containing organic carboxylic acid.The thesis uses the catalyst of the same loading without any organic ligand as the reference agent.The thesis uses dibenzothiophene(DBT)as the model compound of the HDS reaction to investigate the effect of different factors,such as different molar ratio of Mo atom and organic ligand、different introduced sequence of Ni and Mo、different means of heat treatment,on the hydrogenation activity of catalysts prepared.The thesis uses a series of characterization means such as XRD,TEM,H2-TPR,UV-Vis,GC,TG,etc.The experimental results show that under the condition that catalysts have the same metal loading,all three organic ligands can greatly improve the HDS activity of NiMo catalysts,which fully shows the advantage of the metal complex precursor method to enhance the activity of NiMo catalysts.However,different ligands have different effects on promoting the HDS results of catalysts.The promoting order is: CyDTA>NTA>EDTA.Three ligands have different effects on hydrogenation selectivity of catalysts.NTA greatly improves the hydrogenation selectivity of NiMo catalysts,EDTA has a little effect on the hydrogenation selectivity.CyDTA significantly weakens the selective hydrogenation of Ni Mo catalysts.Investigation results about preparation condition of NiMo catalysts prepared with different organic ligands shows that all different introduced sequences of metal can increase HDS activity of the catalyst,wherein the catalyst with Mo introduced first exhibits higher HDS activity than the catalyst with Ni introduced first.Calcination temperature varies HDS activity of the catalysts.For NiMo catalysts prepared with NTA,low calcined temperature from 100 ℃ to 300 ℃ helps to improve catalysts activity.For NiMo catalysts prepared with EDTA,being dried at room temperature has the optimum catalysts activity.NiMo catalysts prepared with CyDTA are not sensitive to calcination temperature from room temperature to 500 ℃.The TPR characterization results confirm that for NiMo catalysts based on bimetallic complex,organic ligands make a substantial increase in the reduction peak temperature and the more the organic ligand,the farther the reduction peak temperature shift to the higher zone.This indicates that organic ligands and metal conponents have direct stronger interaction.All three organic ligands decrease the reduction peak temperature of Ni.NTA and EDTA have no effect on the reduction peak temperature of Mo,CyDTA improves the the reduction peak temperature of Mo.This indicates that organic ligands may coordinate with Ni,and have no interaction with Mo.UV-Vis results also indicate that organic ligand coordinate with Ni preferentially and have no interaction with Mo.Three ligands make the average stacking layers of MoS2 active phase increased,the average length of the platelets increased,the exposure ratio of Mo atoms decreased,TOF values increased greatly,indicating that the nature of MoS2 active phase of the catalyst may have changed.A greater proportion of NiMoS active phase with higher intrinsic activity may be the the root cause of the increased HDS catalyst activity. |
