Selective Catalytic Conversion Of Biomass Sugar And Its Derivative To Furanyl Chemicals

The selective hydrogenation/deoxidation of fructose and furfural(a derivative of xylose)to prepare furanyl chemicals is an effective way to realize their high-value utilization,and the key point is to develop high-efficient catalysts.At present,non-noble metal catalysts with abundant reserves were employed to cleave the C=O bond in furfural due to their relatively high hydrogenation ability.However,non-precious metal catalysts still face huge challenges in terms of enhancing electronic properties,selectively breaking bonds,and improving stability.In addition,the cosolvent only plays a physical role,and its ability is minimal to assist catalyst in cleaving the C-O bond in fructose,resulting in a limited yield of the target product.To tackle the above problems,this dissertation adopts the defect engineering strategy that can control the electronic and chemical properties of catalysts,and the solvent effect strategy which can regulate reaction rate and reaction balance,respectively.Utilizing defect engineering strategy,this dissertation prepared 1)oxygen vacancy-rich Mn3O4 and LaMnO3,which show excellent ability to cleave C=O bond in furfural,and selectively convert furfural into furfuryl alcohol with high yield;2)N,O co-doped carbon-based catalyst(Co/C),which realize efficient cleavage of C=O and C-O bonds during the in-situ hydrogenation of furfural to 2-methylfuran(MF),and a high yield of MF was obtained.In addition,due to the rich defects,the above catalysts all demonstrate high stability.Employing the solvent effect strategy,dimethyl sulfoxide(DMSO),which can assist catalyst to cleave the C-O bond at C2 position of fructose,was adopted and greatly improved the yield of 5methoxymethylfurfural(MMF),the product of the dehydration-etherification of fructose.The main works are summarized as follows:(1)Oxygen-vacancy-mediated Mn3O4 for in-situ hydrogenation of furfural in isopropanol to furfuryl alcohol:Based on the fact that transition metal oxides with oxygen vacancies and mixedvalence can be obtained from organometallic salts by controlling the calcination temperature,oxygen-vacancy-mediated Mn3O4(Mn3O4-CA)was prepared by the direct calcination of manganese(Ⅱ)acetate tetrahydrate at 350℃ for 2 h,and used for in-situ hydrogenation of furfural.Compared with commercial Mn3O4 and Mn3O4 prepared by a traditional method,Raman,X-ray photoelectron spectroscopy(XPS),electron paramagnetic resonance(EPR),and electrochemical impedance spectroscopy(EIS)characterization results reveal that Mn3O4-CA contains oxygen vacancies,and their existence accelerates electron transfer rate.NH3 temperature-programmed desorption(NH3-TPD)results exhibit that oxygen vacancies induce a change in the configuration of Mn valence electrons,which rearranges the surface species,thereby enhancing the acidity of the catalyst.CO2 temperature-programmed desorption(CO2-TPD)results show that unpaired electrons accompanied by oxygen vacancies enhances the basicity of the catalyst.A high yield of furfuryl alcohol(>99 mol%)was obtained from furfural at 220℃ for 4 h in isopropanol.The results of control experiments,adsorption experiments,and kinetic experiments show that oxygen vacancies can improve the adsorption capacity of catalyst for furfural,lower the reaction energy barrier,and thus realize the effective conversion of furfural to furfuryl alcohol.Mn3O4-CA also shows good stability.(2)Oxygen vacancy-rich LaMnO3 for in-situ hydrogenation of furfural in ethanol to furfuryl alcohol:To increase the concentration of oxygen vacancies on catalyst for improving its catalytic activity,oxygen vacancy-rich LaMnO3(LM4C)was synthesized through in-situ substitution of Mn by Co,and used for in-situ hydrogenation of furfural.Compared with pure LaMnO3,Raman,H2 temperature-programmed reduction(H2-TPR),O2 temperature-programmed desorption(O2TPD),XPS,EPR,EIS,CO2-TPD,and NH3-TPD characterization results showthat LM4C contains abundant oxygen vacancies,and their presence enhances the electronic and acid-base properties of the catalyst.A 93.6 mol%yield of furfuryl alcohol was obtained after furfural was catalyzed by LM4C(treated by low concentration of hydrogen)in ethanol at 240℃ for 5 h,which is much higher than the furfuryl alcohol yield(55.6 mol%)under the same reaction conditions with the participation of Mn3O4-CA.The results of adsorption and kinetic experiments show that LM4C owns a stronger adsorption ability for furfural and a lower activation energy for the conversion of furfural to furfuryl alcohol compared with Mn3O4-CA.The rich oxygen vacancies endow LM4C with excellent stability,and its catalytic activity remains almost unchanged after 5 times.(3)N,O co-doped carbon anchored with Co nanoparticles(Co/C)for in-situ hydrodeoxygenation of furfural in ethanol to MF:Through in-situ hydrogenation,furfural can not only be converted into furfuryl alcohol,but also be further deoxidized and converted into MF.A series of supported Co/C catalysts were synthesized by the complexation-pyrolysis method,and used for in-situ hydrodeoxygenation of furfural to MF.By adjusting the coordination environment(species and ratio of heteroatoms)of Co2+in organic ligands,the influence of heteroatoms on the electronic and chemical properties of catalysts was investigated.Compared with catalysts derived from precursors containing only O heteroatoms,only N heteroatoms,and both N and O heteroatoms but with low molecular weight,Raman,EPR,and EIS characterization results present that catalyst(Co-SFB)derived from organic ligands containing both N and O heteroatoms and high molecular weight owns more unpaired electrons and faster electron transfer ability.XPS characterization indicates that the enhanced electronic properties endowthe interface between the metal and the support with stronger interaction.NH3-TPD and CO2-TPD results reveal that N,O co-doping enhances the acidity and basicity of Co-SFB by redistributing the electrons of surface species.Co-SFB catalyzed furfural in ethanol at 240℃ for 3 h,and MF yield was as high as 94.6 mol%.The results of control experiments,adsorption experiments,kinetic experiments,and stability experiments show that the enhanced electronic properties originating from the co-doping of N and O in the carbon matrix endow Co-SFB with excellent reaction activity and stability in in-situ hydrodeoxygenation.(4)DMSO/solid acid system for dehydration-etherification of fructose in methanol to MMF:Besides furfural,biomass fructose can also be used as a feedstock for the production of furanyl chemicals via the deoxygenation route.To stabilize the intermediate product and suppress the side reactions,the polar solvent DMSO with solvent effect was selected as the cosolvent for the dehydration-etherification of fructose in methanol to MMF.The effects of reaction conditions(DMSO dosage,reaction temperature,reaction time,fructose dosage,and solid acid dosage)on MMF yield were investigated.Under the optimized reaction conditions,MMF yield reaches 80.5 mol%.The kinetic experiment results show that the second step of the series reaction is the ratedetermining step.Based on the results of attenuated total reflectance infrared spectroscopy(ATR-FTIR)and control experiments,a possible mechanism was proposed.First,H+on solid acid interacts with DMSO to form[DMSOH]+,which acts as the joint catalyst and then attacks fructose.Specifically,S and O atoms in[DMSOH]+ associate with O and H in hydroxyl on C2 of fructose,and a four-membered ring transition state forms.After the rapid dehydration of fructose,5-hydroxymethylfurfural(HMF)forms.The second-step etherification reaction process is similar to the first-step process,through the formation of a four-membered ring transition state between HMF and[DMSOH]+,dehydration,removal of DMSO,formation of positive ion,and etherification with methanol,and lastly,MMF was obtained.