Preparation Of SO₄^2-/?-Al₂O₃ And Magnetic ?-Al₂O₃ Supported Acidic Ionic Liquids And Their Application On Catalytic Conversion Of Carbohydrates

In recent years,fossil fuels have gradually become exhausted and the energy crisis has approached due to the rapid development of industry and the continuous growth of population.Therefore,it is imminent to find suitable renewable resources instead of fossil resources.Biomass is a rich renewable resource,which can be converted into a variety of platform compounds under suitable catalytic systems.Among them,5-hydroxymethylfurfural?HMF?and furfural two furanyl platform compounds have aroused widespread concern of researchers at home and abroad because of their great potential applications in the production of chemicals and fuels.Therefore,the development of novel and green catalytic systems for preparation of platform compounds from biomass efficiently has important development and significance.In this paper,the preparation of catalysts and the transformation of carbohydrates were studied.The specific contents include the following three aspects:?1??-Al₂O₃ was synthesized by precipitation method and sol-gel method.The ?-Al₂O₃ prepared by sol-gel method was selected as the carrier due to its better performance.A series of SO₄^2-/?-Al₂O₃ catalysts were obtained by impregnating ?-Al₂O₃ with different concentrations of?NH₄?₂SO₄ solution,which were used to catalyze the conversion of galactose into HMF,and the best catalytic activity of SO₄^2-/?-Al₂O₃ was screened out.A galactose conversion of 88.6% and a HMF yield of 38.6% were obtained at 140 ? for 5 h under the action of the best SO₄^2-/?-Al₂O₃ as catalyst and DMSO as solvent.The morphology,composition and thermal stability of the catalysts were analyzed by FT-IR,XRD,SEM and TGA.The above catalytic system has the best catalytic activity on fructose and inulin.At the same time,the catalytic system also has a good catalytic effect on the conversion of xylose to furfural.A furfural yield of 62.1% with a 97.1% xylose conversion was achieved using SO₄^2-/?-Al₂O₃ as the catalyst in DMSO at 140 ? for 3 h.?2?A series of different metal-substituted bifunctional acidic ionic liquids were synthesized and used to catalyze the preparation of furfural from xylose.The best catalytic activity of the bifunctional acidic ionic liquid?BAIL-Al?was screened out.A novel heterogeneous catalyst Fe₃O₄@Al₂O₃-?BAIL-Al?was prepared by immobilizing BAIL-Al on the surface of magnetic ?-Al₂O₃.The morphology,composition,thermal stability and magnetic properties of the catalysts were analyzed by FT-IR,XRD,BET,SEM,TEM,XPS,TGA and VSM.A furfural yield of 67.5% with a 97.3% xylose conversion was obtained using Fe₃O₄@Al₂O₃-?BAIL-Al?as catalyst in DMSO at 140 ? for 3 h.The catalyst could be easily separated and recovered,which also had a great reusability.After five times of recycling,the yield of furfural was 58.7%.In addition,we proposed a plausible reaction mechanism for the preparation of furfural from xylose catalyzed by Fe₃O₄@Al₂O₃-?BAIL-Al?.The process mainly includes the isomerization of xylose into xylulose by Lewis acidic sites and the dehydration of furfural from xylulose by Br?nsted acidic sites.?3?A novel magnetic ?-Al₂O₃ immobilized cross-linked acidic polyionic liquid catalyst Fe₃O₄@Al₂O₃-SH-IM-HSO₄ was prepared and applied in the conversion of xylose.The morphology,composition,thermal stability and magnetic properties of the catalyst was analyzed by FT-IR,XRD,BET,SEM,TEM,XPS,TGA and VSM.A furfural yield of 70.2% with 97.2% xylose conversion was achieved with Fe₃O₄@Al₂O₃-SH-IM-HSO₄ as catalyst and DMSO as solvent at 140 ? for 3 h.The catalyst had a good reusability,and the yield of furfural could reach 62.1% after four times of recycling.In addition,the above catalytic system had the best catalytic effect on the conversion of fructose.A HMF yield of 92.5% with 98.7% fructose conversion was obtained at 120? for 1h.