The Effect Of Boron On Physicochemical Characterization And Hydrotreatment Activity Of NiMo/Al₂O₃ Catalysts

Heavy benzene which is generated in the hydrogenation process of crude benzene can be used as fuel oil.It not only can realize the reasonable utilization of heavy benzene,but also can alleviate the pressure of the oil demand to a certain extent.It can cause environmental pollution in use if not treat well,and this is because of heavy benzene contain a large number of double ring aromatics,nitride and sulfide.Therefore,it is extremely important to study the catalyst with highly hydrogenation activity to reduce the content of sulfur,nitrogen and aromatics in heavy benzene.Boron was added as assistant of NiMo/Al2O3 catalyst,in order to obtain better hydrogenation activity.The B/Al2O3 supports and NiMoB/Al2O3 catalysts which were modified by boron were characterized by N2-BET,XRD,NH3-TPD,C02-TPD and H2-TPR.The effect of boron on the physicochemical property of B/Al2O3 and NiMoB/Al2O3 was obtained by characterization.In order to research the effect of boron on hydrodesulfurization(HDS)hydrodenitrogeneration(HDN)and aromatics hydrogenation(HDA)activity of NiMo/Al2O3 catalysts,the benzothiophene,quinoline and naphthalene were used as model compounds respectively.The result of the characterization showed that boron can dissolve the hole wall of Al2O3 and this could increase the specific surface area of the support when the loading of boron was under 1 wt%.The specific surface area of the support would decrease with continuing to increase boron loading.Boron will reduce the dispersion of active component.The active metal would gather to Mo03 crystal when the loading of boron was greater than 8 wt%,and the Mo03 crystal can block the pores of the catalyst which leads to decreasing the specific surface area of the catalyst quickly.Boron can change the acidity and alkaline of the support and catalyst through consuming the hydroxide radical of Al2O3.The result of NH3-TPD showed that with the increase of boron loading the amount of acid site of the supports and catalysts decrease first and then increase.The result of CO2-TPD showed that the alkali site of B/Al2O3 support would decrease with the increase of boron loading and the alkaline hydroxyl would disappear when the boron loading was 5 wt%.The variation of hydroxyl on the support will change the interaction between support and active metal.From the H2-TPR characterization,we could see that the addition of boron would promote the reduction of octahedral coordination Mo species when the loading of boron was below 0.5 wt%.The reduction peak of MoO3 would appear when the introduction of boron and the intensity of this peak would increase with the increase of the boron loading.From the H2-TPR curve of sulfide catalysts we could see that the introduction of boron can promote the sulfide of the catalysts and produce more sulphur vacancy when the loading of boron was under 0.5 wt%.The activity of the catalysts which modified by boron were investigated by model compounds.The addition of boron can increase MoS2 layer number and produce more hydrogenation activity site.This lead to the increase of hrdrogenation activity of the catalysts,and the NiMoB/Al2O3 had the highest naphthalene hydrogenation activity when the loading of boron was 1 wt%.The introduction of boron would change the activity of hydrodesulfurization and hydrodenitrogeneration of the catalysts.The NiMoB/Al2O3 catalyst had more sulphur vacancy,and better performance of hydrogenation,when the boron loading was 0.1 wt%,and the catalyst had the best activity of hydrodesulfurization and hydrodenitrogeneration.