Density Functional Theory Study On Hydrogenation Reactions Of 1,4-butynediol Over Ni-based Catalysts

Under the background of double carbon,human lifestyle is gradually becoming green and low-carbon.Biodegradable plastics and electric vehicles as green products have a large market,making manufacturing materials in short supply.1,4-butanediol（BDO）,as a raw material for the preparation of biodegradable plastics PBS and lithium-ion battery electrolyte,has a broad prospect.The development of this technical route is of great significance for the realization of the dual-carbon goal in the chemical industry.Based on the technical innovation of efficient hydrogenation catalyst,it is a common concern of the industry and academia at present to reduce the occurrence of side reactions such as isomerization and hydroxyl aldol condensation,and to achieve the highly selective hydrogenation of 1,4-butynediol for the targeted synthesis of 1,4-butanediol.However,due to the complexity of BYD hydrogenation process and the unclear structure of catalyst prepared in laboratory,the reaction mechanism of BYD hydrogenation process is poorly recognized at present.The traditional"trial and error"method is still used in the development of new catalysts,which is not efficient.In this paper,the typical Ni and Ni-Fe alloy catalysts were taken as the research object,and the reaction mechanism of BYD on different crystal surfaces of Ni and Ni-Fe alloys was investigated based on density functional theory,which provided theoretical guidance for the design of new Ni-based BYD hydrogenation-oriented synthesis BDO catalysts.The main research contents are as follows:1.The hydrogenation reaction processes of BYD on Ni crystal surfaces were compared,including the low index crystal surfaces Ni（111）,Ni（100）and Ni（110）and the high index crystal surface Ni（211）.The adsorption of reactive species on Ni surfaces was investigated,and it was found that the adsorption energy of BYD>cis-BED>BDO,that is,as the degree of hydrogenation increased,the adsorption energy of the species became smaller,which was favorable for product desorption.Based on the Horuiti-Polanyi mechanism,the hydrogenation of BYD to cis-butenediol（cis-BED）/trans-butenediol（trans-BED）and further hydrogenation to BDO were calculated.It was found that the energy barrier for the formation of cis-BED was much lower than that of trans-BED.In the whole process of BYD hydrogenation to BDO,cis-BED hydrogenation to alkyl intermediate（BEDH）is the rate-determining step.The energy barriers on the four crystal surfaces were compared,and it was found that the energy barriers on Ni（111）and Ni（110）were 0.77 e V and 0.80 e V respectively,which showed excellent hydrogenation activity.The formation of BEDH undergoes parallel reactions of hydrogenation to BDO and isomerization toγ-hydroxybutyraldehyde（γ-HALD）.The energy barrier of isomerization of BEDH on Ni（110）and Ni（100）is higher than that of H（0.97 e V vs.0.63 e V;0.94 e V vs.0.66 e V）,which is favorable for hydrogenation to produce BDO.For the generatedγ-HALD,there were parallel competitive reactions of hydrogenation to BDO and cyclization to 2-hydroxy-tetrahydrofuran（HTHF）.It was found thatγ-HALD was more easily converted to the main product BDO（0.82 e V;1.64 e V）,and more easily cyclized to HTHF on Ni（111）,Ni（100）and Ni（211）.In conclusion,the hydrogenation of BYD on Ni（110）is conducive to the generation of BDO,and even ifγ-HALD is generated,it will preferentially transform into BDO on this surface.2.Ni-Fe alloy catalysts were constructed on pure Ni crystals,and the mechanism of BYD hydrogenation reaction on Ni₁Fe₁（111）and Ni₃Fe₁（111）surfaces was discussed.Bader charge analysis was performed on the Ni-Fe alloy,and it was found that the charge density of the surface Ni atoms gradually increased with the increase of Fe content.The activation energy and heat of reaction along the reaction path were calculated.On the Ni₁Fe₁（111）surface,the rate-determining step of hydrogenation of BYD to BDO was cis-BED hydrogenation to BEDH,and the energy barrier was 1.06 e V.The rate-determining step on the Ni₃Fe₁（111）surface is BYD hydrogenation to BYDH with an energy barrier of 0.70 e V.Therefore,the hydrogenation activity of Ni₃Fe₁（111）surface is the highest.Then the reaction of isomerization of BEDH toγ-HALD was investigated.The hydrogenation and isomerization energy barrier（0.66 e V;0.64 e V）on Ni₃Fe₁（111）surface were lower than the Ni₁Fe₁（111）（0.89 e V;0.81 e V）.Therefore,Ni₃Fe₁（111）surface showed higher reactivity than Ni₁Fe₁（111）surface.However,the isomerization energy barrier on Ni₃Fe₁（111）is lower than the hydrogenation energy barrier,and this surface is more prone to isomerization reactions and is not favorable for the formation of the hydrogenation product BDO.