Modification Of Molybdenum-based Catalytic Materials And Their Catalytic Performance Of Hydrodesulfurization Of 4,6-dimethyldibenzothiophene

Most of the world's crude oil contains more organic sulfur compounds,so it needs to be desulfurized before it can be used.Hydrodesulfurization(HDS)is the most widely used and effective desulfurization method in the industry.In this thesis,the effects of the morphology,surface pH and interaction between the carrier and the active components on the catalysis of HDS activity were studied after the V-Al2O3 support was modified by cerium and magnesium.The causes of the changes in the catalytic activity of HDS were studied in detail using modern physics techniques such as TEM,STEM,XRD,CO2/NH3-TPD,NEXAFS and so on.The(Ce)-Al2O3 support and(Ce)/Al2O3 support were synthesized by different methods.The morphology,crystal structure,pore size and surface acidity of supports were analyzed.It was found that the introduction of cerium did not change the overall morphology of the support,but had a significant effect on the crystallinity and specific surface area of Al2O3.At the same time,the introduction of cerium can produce Bronsted acid sites on the surface of Al2O3 carrier to promote the vulcanization of Mo species,and the introduction of cerium by one-step method can generate more Br(?)nsted acid sites.Finally,the introduction of cerium can significantly reduce the interaction between the Al2O3 support and the active metal,making it easier for Mo6+ to be reduced to Mo4+,resulting in more Co-Mo-S active phase.Therefore,the cerium modified catalyst has higher hydrodesulfurization activity,and the desulfurization rate of 4,6-dimethyldibenzothiophene reaches 72.65%at 320?C for the CoMo/(Ce)-Al2O3 catalyst.In this paper,the influence of the introduction of Mg and its introduction method on the hydrodesulfurization activity of 4,6-dimethyldibenzothiophene was investigated.It was found that the introduction of magnesium by one-step method and two-step method can significantly improve the hydrodesulfurization activity of the catalyst,and the performance improvement by one-step method is more obvious.In addition,we have adjusted the Mg/Al content in the one-step method.It can be found that wihen MgO/Al2O3=0.2,the CoMo/(Mg)-Al2O3 catalyst has the highest hydrodesulfurization activity.The reason is analyzed by a series of characterizations.First,the one-step catalyst shows the ?-CoMoO4 phase,while the two-step catalyst shows the mixed phase of ?-CoMoO4 and ?-CoMoO4,and ?-CoMoO4 is easier to form Co-Mo-S active phase.The formation of inert Co3O4 and CoAl2O4 can also be reduced to some extent.Secondly,the introduction of magnesium by one-step method mainly increases the amount of medium-strong alkali,and the medium-strong alkaline site can avoid the polymerization of molybdenum substance,and can neutralize some acidic sites,thereby inhibiting the formation of coke to a certain extent.Finally,the introduction of magnesium can enhance the interaction between the carrier and the active component,promote the dispersion of molybdenum,and also inhibit the reduction of ?-CoMoO4 to Co2Mo3O8.