Computational Studies On The Precise Control Over Ni-based Catalysts Towards Furfural Catalytic Conversion

With the depletion of fossil resources and the deterioration of environmental pollution,the utilization of sustainable energy has attracted considerable attention.Biomass is a non-fossil carbon source,which is expected to replace fossil fuels to some extent.Furfural,one of the biomass platform molecules,can convert to various high value-added products,involving biofuel,and green solvents,etc.The Ni-based catalysts have attracted much attention due to low price and excellent hydrogenation performance.Recently,Ni catalysts show excellent performance for the reduction of C=C and C=O bond.However,in order to achieve desirable products with high selectivity,the following key problems should be solved:(1)studies on reaction mechanism for furfural conversion and quantitative structure-function relationship are lacking.(2)studies on modulation strategies for active site of Ni catalyst and theoretical design principles are unclear.In this work,a series of Ni-based catalysts with diverse local environment were designed and used to study furfural conversion reactions.(1)studies on reaction mechanisms,potential energy surface,as well as the effect of geometric/electronic structure on product selectivity by using density functional theory(DFT)method;(2)investigations on reaction rate and product distributions under various reaction conditions through microkinetic modeling,so as to reveal the relationship between reaction conditions and adsorption configuration,product distribution.The catalyst structures were described and quantified to reveal the effect of the local environment of the intrinsic active sites on the reaction,further to obtain the intrinsic rule between catalyst surface structure and the performance for furfural conversion.This work provides a feasible idea and valuable theoretical basis for structure-property relationship of biomass conversion and structural design of metal catalyst.The specific contents are as follows:1.Studies on coordination environment of Ni catalysts towards selective conversion of furfuryl alcoholPeriodic density functional theory calculations and microkinetic modeling were combined to systemically examine the reaction energetics and kinetics of furfuryl alcohol conversion on different kinds of active sites.Nine surface terminations of Ni with various coordination numbers were built to represent various terrace,step,and corner sites.Calculations on the adsorption configuration of furfuryl alcohol show that flat adsorption is the most favorable for all nine surfaces,and adsorption is especially favored for step site.Barrier height analysis indicates that terrace sites favor hydrogenation to tetrahydrofurfuryl alcohol whereas corner sites facilitate C-OH scission to produce 2-methylfuran;whilst furfuryl alcohol is not favorable product on all surfaces.Microkinetic modeling is employed to calculate the product selectivity on a step site under experimental conditions.At lower temperatures and higher generalized coordination number,tetrahydrofurfuryl alcohol is the most favorable product;while the selectivity to 2-methylfuran is higher at higher temperature and lower generalized coordination number.Therefore,the changes of geometry and coordination environment of the active site determine the adsorption configuration,further resulting in selectivity difference.2.Studies on Ni-based bimetallic catalysts towards furfural hydrodeoxygenation reactionHDO of FAL to 2-methylfuran over 17 kinds of Ni-based bimetallic catalysts were systematically studied.Periodic density functional theory calculation reveals the electron transfer from secondary M to Ni atom,the Ni-based partner(3d,4d metals)imposes an important influence on the catalytic performance toward FAL HDO reaction,which modifies Ni electronic environment and induces bimetal d orbital overlap,giving rise to changes in adsorption configuration and reaction activity.The reaction mechanism and potential energy surface indicate a competition between C-OH scission and hydrogenation.A specific correlation between oxygen binding energy(OBE)value and energy barrier of C-OH scission/*OH species hydrogenation suggests that OBE serves as the most appropriate descriptor to characterize the activity of bimetallic catalysts.A trade-off of OBE value(from-4.00 to-2.00 eV)has been built to promote C-OH scission and hydrogenation activity simultaneously,in which Ni-M(M=Fe,Co,Mo,or Ru)bimetallic catalysts show the prominent catalytic performance.Catalytic evaluations verify that OBE can be used to judge the performance of hydrodeoxygenation catalysts.The key to designing bimetallic catalyst is the intrinsic characteristics and electronic effects of secondary metal.3.A precise control of NiMo bimetallic catalyst and studies on reaction mechanism of hydrodeoxygenationBased on DFT calculation and microkinetic modeling,the furfural hydrodeoxygenation to 2-methylfuran reaction over NiMo bimetallic catalyst with three Mo contents(Mol/Ni(111)surface,Mo2/Ni(111)surface and MoNi(111)surface)were investigated.Bader charge analysis demonstrates electron transfer from Mo to Ni atom.Reaction pathways(two hydrogen sources),potential energy surfaces,and rate-determining step of overall reaction were discussed.On Mo 1/Ni(111)surface with monodispersed Mo,OH species shows excellent hydrogenation activity,which results in FAL conversion to 2-methylfuran by OH path.Conversely,MoNi(111)surface has an obvious preference for H path.The results of microkinetic modeling further illustrate that Mo2/Ni(111)is inclined to OH path for FAL conversion to 2-methylfuran.The TOF value of 2-methylfuran also shows Mol/Ni(111)exhibits the highest catalytic activity in three surfaces.Therefore,contents of secondary metal in the bimetallic catalyst affects the reaction mechanism,and further changes the catalytic activity.4.Studies on PtNi single atom alloy catalysts towards selective ring-opening reaction of furfuryl alcoholMaking full use of the advantages of single atom alloy(SAA)catalysts,the selectivity of ring-opening reaction of furfuryl alcohol over Pt1Ni(111)and Pt1Ni(211)surfaces were studied.DFT calculation shows that the adsorption of furfuryl alcohol on SAA surface is stronger than that on Ni(111).In particular,Pt1Ni(211)with low-coordinated Pt has larger adsorption energy.The reaction mechanism and potential energy surface indicate that the product selectivity of ring-opening reaction depends on the adsorption configuration of furfuryl alcohol.The energy barriers analysis show that on PtiNi(111)surface,intermediate resulting from hydrogenation at the C2 and C3 positions prefers to ring-opening reaction.Thus,the formation of 1,5-pentanediol was identified as the favorable product.However,on Pt1Ni(211)surface,the C-O bond of furfuryl alcohol was directly cleaved to produce 1,2-pentanediol,indicating the high ring-opening ability of single Pt atom at the step site.Therefore,PtNi-SAA catalyst has excellent catalytic activity,and coordination number of Pt determines the selectivity of ring-opening reaction.