Research On Selective Catalytic Hydrogenation Of Furfural To High-value Chemicals

Making use of biomass resources to produce sustainable high-value chemicals is conducive to alleviating the growing environmental,energy and economic problems caused by the massive exploitation and overconsumption of fossil resources.As one of the biomass-based feedstocks,lignocellulose mainly consists of cellulose,hemicellulose and lignin,and the high-value conversion of its derivatives is the key to biomass utilization.In this thesis,a series of Pt-based nanocluster catalysts and nitrogen-doped carbonencapsulated catalysts were prepared.The synthesis and structure regulatory mechanisms of these catalysts were systematically investigated to evaluate the catalytic performance in the process of furfural hydrogenation and rearrangement to oxygenated chemicals.In addition,the related reaction mechanisms and catalyst conformation relationships were verified by various characterization methods.The application of biomass derivatives for the preparation of oxygenated value-added chemicals was broadened.Effective cascade of furfural hydrogenation and rearrangement processes under mild conditions was also achieved.The main research of this paper is discussed in the following three aspects:Pt/WOx nanocluster catalysts for the weak hydrogenation of furfural to furfuryl alcohol was firstly investigated in the thesis.The physicochemical properties of the catalysts were compared at different loadings and calcination temperatures.Through reducing the size of the Pt phase in the catalysts within a certain cluster scale,nanocluster catalysts with high catalytic activity were prepared.The reaction conditions were screened and 98.3%yield of furfuryl alcohol was obtained in ethanol solvent at a reaction temperature of 40℃.The chemical reaction kinetic analysis carried out showed that the catalyst possessed a very low apparent activation energy of 12.82 kJ/mol and a TOF value of 1984.7/h.During the process,furfural was adsorbed in the configuration of η2(C,O)-aldehyde group to the Pt6+ active center with several ensemble atoms,indicating that Pt nanoclusters were the most active structures in this catalytic reaction.Eventually,the C=O group was selectively hydrogenated to CH-OH under mild conditions of low temperature and low loading.Based on the hydrogenation from furfural to furfuryl alcohol,the nitrogen-doped carbon-encapsulated catalyst Co@NC was synthesized and used for the preparation of cyclopentanone by hydrogenation and rearrangement of furfural.Through comparing the different monometallic nitrogen-doped carbon-encapsulated catalysts,it was determined that the Co-based catalysts have superior catalytic activity for the preparation of cyclopentanone from furfural.The optimal carbon nanotube encapsulation structure was obtained by changing the calcination temperature to regulate the percentage of different Co phases and N species in the carbon-encapsulated catalysts.The doping of nitrogen promoted the electron transport ability,and the total yield of cyclopentanone derivatives reached 96.6%under the screened optimal reaction conditions.Then furfuryl alcohol is clearly identified as an intermediate in the hydrogenation and rearrangement of furfural to cyclopentanone derivatives.In addition,Sn with strong Lewis acid properties was introduced in the catalyst fabrication,but the bimetallic CoSn@NC did not exhibit good catalytic rearrangement effects.In order to further solve the problem of high hydrogenation rearrangement reaction temperature,on account of the superior performance of Pt/WOx nanocluster catalyst,the hydrogenation and rearrangement from furfural to cyclopentanol through Pt/MoOx nanocluster catalyst was investigated.Different calcination temperatures and loading conditions were screened,and finally 1.Owt%Pt/MoOx-750 nanocluster catalyst was selected.The reaction was carried out at 140℃ and 5 MPa H2 pressure for 12 h.For the successive hydrogenation and rearrangement reaction,the yield of cyclopentanol reached 96.7%.The fitting results of the first-stage reaction kinetic equation showed that the rearrangement reaction was the decisive speed step that determined the total course of the reaction.In this successive process,the fully exposed Pt6+ active center was adsorbed by furfural and cyclopentanone in the conformation of η2(C,O)-aldol andη1(O)-aldol configurations,respectively.The hydrogenation and rearrangement in the aqueous phase from furfural to cyclopentanol was accomplished through the hydrogen transfer mechanism.