The Study On Selective Hydrogenation Of Maleic Anhydride Catalyzed By ZrO₂ Supported Nickel Catalyst

The hydrogenation of maleic anhydride?MA?to produce high value-added chemicals can be regarded as effective routine to utilization of coral resource,clean and efficient use of coal resources and realize transformational development.MA can be obtained by oxidation of coking benzene and butane.Its hydrogenated products,such as succinic anhydride?SA?,?-butyrolactone?GBL?,tetrahydrofuran?THF?and 1,4-butanediol?BDO?,are high value-added fine chemicals,which are widely used in military,textile,petrochemical,pesticide and other fields.Taking coking benzene,a by-product of coal coking,as a raw material,to extend the downstream chemical industry chain of MA,design and prepare high efficient selective catalysts in hydrogenation of MA to synthesis different target products,explore the relationship between catalyst structure and catalytic performance,is of important scientific significance and practical application value.ZrO₂ has both redox,acidity and alkalinity properties,and exhibits excellent catalytic performance in many reactions as a catalyst or support.For the hydrogenation reaction,the research on ZrO₂ supported metal catalysts mostly focused on the influence of ZrO₂ crystal phase.However,the conclusions obtained by different research groups were quite different.In order to better understand the intrinsic influence of ZrO₂ supported nickel catalyst on the catalytic performance of MA hydrogenation,different characterization methods like Raman,XPS,H₂-TPD,H₂-TPR were used to study of the structure-activity relationship between the surface structure of the catalyst and the hydrogenation performance of MA.The relationship between the surface oxygen vacancies of Ni/ZrO₂ catalyst and its C=O hydrogenation performance was found.Based on this,the scientific rules of the internal relationship between ZrO₂ surface structure,the metal-support interaction,the electron properties surface oxygen vacancies on Ni/ZrO₂ catalyst and the performance of catalyst in MA hydrogenation were further explored.The main research contents and conclusions of this thesis are as follows:1.A series of ZrO₂ supports with different structural properties were prepared using hydrothermal synthesis method,and the performance of its supported nickel catalyst in MA hydrogenation was investigated.The results showed that the prepared ZrO₂ was a tetragonal phase structure when the hydrothermal time was 2 h,and its supported nickel catalyst had almost no C=O hydrogenation activity with the SA as the main hydrogenation product.When the hydrothermal time was more than 4 h,the prepared ZrO₂ was a monoclinic phase structure.The number of surface oxygen vacancies on Ni/ZrO₂ catalyst promoted by the interaction between the nickel species and the ZrO₂ support were first increased and then decreased.Meanwhile the C=O hydrogenation activity of the catalyst also increased first and then decreased.The catalyst with the most promoted oxygen vacancies exhibited the highest C=O hydrogenation activity.It is speculated that the surface oxygen vacancies of the catalyst participate in the C=O hydrogenation and promote the hydrogenation of C=O.2.To further reveal the effect of surface oxygen vacancies on the hydrogenation of C=O for ZrO₂ supported nickel catalysts,In this paper,the formation of surface oxygen vacancies on the surface of Ni/ZrO₂ catalyst and the variation of its structural properties were studied using ZrO₂?2h?and ZrO₂?14h?as support.The intrinsic relationship between the surface structure of Ni/ZrO₂ catalyst and the distribution of hydrogenated products of MA was investigated.It was found that the C=O hydrogenation activity of Ni/ZrO₂ catalyst is closely related to the electron properties of surface oxygen vacancy on the Ni/ZrO₂ catalyst.The surface oxygen vacancy on the monoclinic ZrO₂ supported nickel catalyst was relatively electron-deficient,which can effectively activate the C=O group and cooperate with its neighboring Ni0 to complete C=O hydrogenation.However,the surface oxygen vacancy of the tetragonal phase ZrO₂ supported nickel catalyst had a higher charge densityand was relatively rich in electrons,which made it difficult to activate the C=O group effectively.Therefore,the tetragonal ZrO₂-supported nickel catalyst had almost no C=O hydrogenation activity.3.Based on the above comparative results of monoclinic ZrO₂ and tetragonal ZrO₂ supported nickel catalysts,it was found that the electronic properties of the surface oxygen vacancies on the Ni/ZrO₂ catalyst are the important factor affecting the C=O hydrogenation activity.On this basis,this paper further discussed the structure-activity relationship between the surface structure of ZrO₂ supported nickel catalyst and the hydrogenation performance of MA,in which the ZrO₂ support was composed of monoclinic phase and tetragonal phase mixed phase.The results showed that the mixed crystal phase ZrO₂ supported nickel catalyst exhibited the same structure-activity relationship rule with single crystal phase ZrO₂ supported nickel catalyst in the hydrogenation of MA.The surface oxygen vacancies of the Ni/ZrO₂ catalyst could adsorb C=O groups regardless of electron-deficient or electron-rich,but only the relatively electron-deficient oxygen vacancies can effectively activate the C=O group in the succinic anhydride molecule,and cooperating with its neighboring Ni0 to hydrogenate C=O,obtaining a deep hydrogenation product,?-butyrolactone.The relatively electron-rich oxygen vacancies had a weak ability to activate the C=O group,and it was difficult to effectively activate the C=O group in the SA molecule,so that there was almost no C=O hydrogenation activity in the MA hydrogenation reaction.4.In order to further investigate the influence of the surface structure of ZrO₂ on the surface oxygen electron properties and C=O hydrogenation performance of Ni/ZrO₂ catalyst,the surface structure properties of ZrO₂ support were effectively controlled by doping the hetero atom Sc into ZrO₂.The effect of the surface structure of ZrO₂ support on the hydrogenation performance of the supported nickel catalyst in MA hydrogenation was studied.It was found that the surface structure of ZrO₂ support was different,which leads to different interaction degree between nickel species and ZrO₂ support.The degree of interaction further changed the electronic properties of oxygen vacancies on the surface of Ni/ZrO₂ catalyst and its C=O hydrogenation activity.The ZrO₂ support which was rich in stable oxygen ions and relatively electron-rich oxygen vacancies on surface,which has weak interaction with nickel species,the nickel species promote the generation of oxygen vacancies on the surface of Ni/ZrO₂ catalyst.The relative electron-deficient oxygen vacancies can effectively activate the C=O group,thereby promoting C=O hydrogenation.The ZrO₂ support which was rich in low coordination oxygen ions and relatively electron-deficient oxygen vacancies,interacted strongly with nickel species,a small amount of nickel species entered the ZrO₂ structure or oxygen vacancies,which in turn made the average charge density of surface oxygen vacancies on Ni/ZrO₂ catalyst increased,and their ability to activate the C=O group was weakened,and thus the corresponding C=O hydrogenation activity of the catalyst was reduced,even without C=O hydrogenation activity.