Molecular Design And Experimental Study Of Dual Acidic Catalysts For Cellulose Conversion

Cellulose is a very abundant and sustainable resource.However,the conversion of cellulose to 5-HMF in high yields is difficult owing to the recalcitrant and heterogeneous nature of cellulose.Recently,studies revealed that Br（?）nsted and Lewis acidic ionic liquids can catalyze the conversion of cellulose to 5-hydroxymethylfurfural in different tandem reaction steps.However,excessive amounts of Br（?）nsted acid or Lewis acid accelerated the side reaction,and the yield of 5-HMF will decrease.Therefore,it is important to optimize the ratio of the B/L acid catalyst.In this work,Br（?）nsted–Lewisacidic ionic liquids（ILs）and Br（?）nsted–Lewis acidic Deep Eutectic Solvents（DES）with different Br（?）nsted acid and Lewis acid ratios were designed,which can catalyse the conversion of cellulose to 5-HMF in different tandem reaction steps.Based onquantification calculations,the strength of Br（?）nsted acid and Lewis acid in ILs with different B/L acid ratios were predicted.The catalytic activity of the catalyst with different B/L acid ratio was predicted by the SMD solvation model and the frontier orbital energy theory.This research has the potential to shorten the cycle and cost of catalysts by providing an important theoretical and practical screening method for the directed design of synergistic catalysts in tandem reactions.The specific research contents of this work are as follows:1、Based on density functional theory,the structure optimization and frequency of reactants,catalysts,and catalytic systems are calculated using quantum chemical calculation to ensure the most stable system.Calculating the stabilization energy and LUMO energy of the catalytic system by density functional theory,and thus predict the strength of Br（?）nsted acid and Lewis acid in ILs with different B/L acid ratios.Cellobiose was used as a model molecule for cellulose,and glucose and fructose as the reactants of each step in the series reaction to calculate the HOMO-LUMO gap of the catalytic system by the SMD solvation model and the frontier orbital energy theory,and thus predict catalytic activity under the solvent condition of different reaction steps.According to the energy span model,evaluate the catalytic activity of Br（?）nsted–Lewis acidic ionic liquids with different B/L acid ratios was ordered as follows:[（HSO₃-P）₂im]Zn Cl₃>[（HSO₃-P）₂im]Zn₃Cl₇>[（HSO₃-P）₂im]Zn₂Cl₅>[HSO₃-Pmim]Zn₂Cl₅>[HSO₃-Pmim]Zn₃Cl₇>[HSO₃-Pmim]Zn Cl₃>[（HSO₃-P）₂im]Cl>[HSO₃-Pmim]Cl>Zn Cl₂。2、Six types of ILs were synthesised,and the structure of ILs was characterized by FT-IR and ESI-MS.The Br（?）nsted acidic and Lewis acidic of ILs with different B/L acid ratios were characterized by pyridine infrared spectroscopy.Cellobiose as the model compound for cellulose to study the effect of catalysts with different B/L acid ratios on the yield of 5-HMF under the same conditions.It was found that[（HSO₃-P）₂im]Zn Cl₃exhibited the highest efficiency with a 5-HMF yield of 65.66%,as predicted.The accuracy of the theoretical calculation was verified.In addition,the effect of reaction temperature and time,solvent dosage,catalyst dosage on the yield of 5-HMF was investigated.3、Choline chloride,citric acid and zinc chloride were mixed in different ratio,the choline chloride/citric acid·zinc Br（?）nsted–Lewis acidic DES with different B/L acid ratios were synthesised.Cellobiose as the model compound for cellulose to study the effect of DES catalysts with different B/L acid ratios on the yield of 5-HMF under the same conditions.It was found that when the molar ratio was choline chloride:citric acid:zinc chloride=2:1:2,DESexhibited the highest efficiency with a 5-HMF yield of 36.88%.In addition,the effect of reaction temperature and time,solvent dosage,Zinc chloride dosage and catalyst dosage on the yield of 5-HMF was investigated.