Study On Electrochemical Conversion Of 5-hydromethylfurfural Controlled By Valence State Of Bimetallic CuNi

Due to the energy crisis and global warming,preparing the high value-added chemicals from renewable biomass resources has broad application prospects.The hydrolysate of lignocellulose,5-hydroxymethylfurfural(5-HMF),is an important biomass-derived platform compound.It has been considered to be a "building block"for biorefinery and can be used to prepare high value-added furandicarboxylicacid(FDCA)and dimethylfuran(DMF)by oxidation and reduction of 5-HMF,respectively.FDCA is a chemical intermediate with good stability,and DMF is considered as an ideal liquid fuel.Therefore,the production of FDCA and DMF from 5-HMF has attracted great attention.The existing reports use electrochemical methods under room temperature,room pressure and oxygen/hydrogen-free conditions.Moreover,the reported efficient catalysts are mainly composed of the non-precious metals.Compared with thermochemical methods,it has the advantage of green environmental protection.However,the reported electrochemical catalyst only uses single metal,and catalytic performance needs to be improved.Also,there is a disadvantage of uncertain valence state of the metal and huge metal comsumption.For optimizing the the above shortcomings,we utilize the synergy of bimetals to design catalyst and determine the best catalyst composition and metal valence state for 5-HMF highly selective directed catalytic conversion,which provides a new pathway for the efficient preparation of FDCA and DMF.In this thesis,we use electrochemical methods for the conversion of 5-HMF.By controlling the metal composition and valence state of non-noble metal catalysts(also known as the electron density of surface of different metals),the optimized catalysts with the best electrocatalytic activity and electrochemical performance were screened out.The working portenil was reduced and the current density was improved.As a result,the electrochemical oxidation and reduction of 5-HMF into FDCA and DMF respectively were realized.The regulation of reaction process was also studied,and both structure of the bimetallic catalyst and reaction mechanism were revealed.The main work is as follows:In the electrooxidation section,Cu-Ni catalysts with different Cu-Ni ratios and metal valence states were prepared by incipient-wetness impregnation and aqueous-phase reduction methods.XPS,XRD,FTIR,H2-TPR and TEM characterizations revealed the valence state of Cu and Ni,crystal structure,particle size and reduction behaviors for different catalysts.The catalytic activity and electrochemical performance of Cu-Ni catalysts with different Cu-Ni ratios were investigated.Additionally,the reaction pathway of catalytic oxidation of 5-HMF and reusability of the optimized catalyst were investigated.The conclusions are as follows:1)bimetallic CuNi(OH)4/C showed better catalytic activity than monometallic Cu(OH)2/C and Ni(OH)2/C,as well as CuNi/C catalyst prepared by aqueous-phase reduction method.2)The XRD,H2-TPR and EDS-mapping results confirmed that Ni(OH)2 and Cu(OH)2 form a uniform solid solution structure in the bimetallic catalysts.3)99%conversion of 5-HMF,94%yield of FDCA,97%Faraday efficiency of FDCA and current density of 9.2 mA/cm2 were achieved over CuNi(OH)4/C catalyst under optimized reaction conditions(5 mM HMF,pH=14,1.45 V vs RHE).4)More than 95%conversion of 5-HMF,90%yield and 97%Faraday efficiency of FDCA still maintained after repeated use for 3 times.In the electroreduction section,Cu-Ni catalysts with different metal valence states,metal ratios and metal loadings were also prepared by incipient-wetness impregnation and aqueous-phase reduction method.The catalytic activity and electrochemical performance of Cu-Ni catalysts,Fe-Ni catalysts and Co-Ni catalysts with different metal ratios were investigated.The catalytic performance of different solution systems were evaluated.The reduction working portentil of 5-HMF were optimized.The conclusions are as follows:1)CuNi/C-H2 catalyst prepared by incipient-wetness impregnation method exhibited better catalytic activity than CuNi/C prepared by aqueous phase reduction method.2)Regulating sulfuric acid-ethanol ratio optimized solution microenvironment to enhance the H+activity and increase the solubility of intermediate products,which promoted the electroreduction hydrogenation of 5-HMF.3)The 54%conversion of 5-HMF,35%yield of DMF and 81%Faraday efficiency of DMF were obtained over 2CuNi/C-H2 catalyst under optimized reaction conditions(10 mM HMF,sulfuric acid-ethanol ratio=1:1,pH=0.5,-0.5 V vs RHE).