Mechanistic Exploration Of Directed Conversion Of Cellulose-based Biomass Into Furan Compounds

With the depletion of fossil fuels and growing concerns about global warming,the importance of environmentally friendly and sustainable use of energy is becoming increasingly apparent.Biomass resources are considered as the most promising sustainable resource in the world and have attracted a lot of attention due to their wide source of lignocellulose and high resource conversion value.However,current treatment technologies still rely on many chemical additives and incineration,which cause serious pollution to the environment while also resulting in huge energy consumption.In lignocellulose,cellulose is one of its main components,with a content of up to 30%-50%.However,its high crystallinity and molecular weight make its conversion into high value-added platform compounds challenging.In this study,we developed an efficient catalytic system and reaction conditions to selectively convert cellulose-based biomass into furan-like platform compounds,and the conversion products are widely used in the production of advanced biofuels,bio-based chemicals and pharmaceutical intermediates with high conversion value.Therefore,the development of efficient green catalytic systems for the selective conversion of lignocellulosic biomass into high value-added furan-based platform compounds,in combination with the structural characteristics of lignocellulose itself,will provide a theoretical and practical basis for the high-value utilization of renewable resources worldwide.This paper first prepared a magnetic H₆P₂W₁₈O₆₂@Fe₃O₄/T-NH₄Cl（n=wt%）catalyst for cellulose conversion to achieve a high yield of 5-HMF.The clever use of magnetic separation technology enables the catalyst and residual reactants to be reused.Furthermore,an efficient H₆P₂W₁₈O₆₂@Fe₃O₄/T-NH₄Cl（15%）and DMSO/H₂O catalytic system was established through multi-factor regulation.In practical engineering applications,pretreated corn straw biomass can be converted into furan-based platform compound 5-HMF in small-scale trials.Subsequently,to address the broad application scope,complex preparation process,and low yield of the advanced product DFF of the furan-based compound 5-HMF,a highly efficient transformation from 5-HMF to DFF was designed and synthesized using a simple solvothermal method with the Mn₃O₄/T-NH₄Cl catalyst.The main conclusions drawn from the above work are as follows:（1）A highly efficient conversion of pure cellulose-based biomass to 5-HMF was achieved using H₆P₂W₁₈O₆₂@Fe₃O₄/T-NH₄Cl（15%）catalyst,which was characterized by IR,XRD,VSM,and SEM.Under the reaction conditions of 0.15 g cellulose,15 h reaction time,0.4 g catalyst,160℃temperature,and DMSO:H₂O=9:1 solvent ratio,the cellulose conversion rate was 98.6%,and the yield of 5-HMF was 54.5%.This was mainly attributed to the strong adsorption of T-NH4Cl to cellulose molecules via hydrogen bonding between OH or C-O-C in cellulose and N-H or C-N in T-NH₄Cl,which facilitated the approach of the active site to the reactant;the promotion of electron transfer from T-NH₄Cl to H₆P₂W₁₈O₆₂,which facilitated the cleavage ofβ-1,4-glycosidic bonds in cellulose and the hydrolysis of glucose;and the suitable coexistence of Br?nsted acidic and basic sites in H₆P₂W₁₈O₆₂@Fe₃O₄/T-NH₄Cl（15%）,which facilitated the hydrolysis of cellulose,isomerization of glucose to fructose,and subsequent dehydration to 5-HMF.The introduced magnetic property enabled efficient separation of the catalyst from the reaction residue,enabling its recyclability while maintaining its activity.（2）Corn stover,an actual lignocellulosic biomass,was pretreated with Na OH at different temperatures.IR,XRD,and SEM characterization techniques were used to show that the obtained cellulose-based biomass effectively removed lignin and hemicellulose,reduced intramolecular hydrogen bonds and polymerization degree,and significantly increased surface roughness while maintaining the basic structure of cellulose.Based on this,a conversion of92.3%and a yield of 51%of 5-HMF were achieved using 0.4 g H₆P₂W₁₈O₆₂@Fe₃O₄/T-NH₄Cl（15%）catalyst under the reaction conditions of 15 h reaction time,160℃temperature,and DMSO:H₂O=9:1.This demonstrated the efficient conversion of actual cellulose-based biomass to furan compounds,specifically 5-HMF.（3）Mn₃O₄/T-NH₄Cl（120）catalyst was prepared and characterized by IR,XRD,XPS,and BET techniques,enabling efficient conversion of furan compound 5-HMF to DFF.Under the reaction conditions of 200 mg catalyst,14 h reaction time,120℃temperature,20 ml/min oxygen flow rate,and DMSO solvent,the conversion rate of 5-HMF was 100%,and the yield of DFF was 89.4%.The catalyst was able to maintain its high activity after 8 repeated uses while retaining its stable structure.The mechanism of the cleavage of 5-HMF bonds and the catalytic oxidation reaction pathway were derived by analyzing the reactive oxygen species generated during the reaction process and the Mn⁴⁺/Mn²⁺redox cycle.