Morphology-controlled Preparation Of Nitrogen-Doped Carbon-Based Acidic Ionic Liquids And Their Applications In Biomass Conversion Reactions

The problem of energy and environment is one of the most important research topics in the green chemistry field.The rapidly decreasing fossil resource and air pollution caused by hydrocarbons,NOx,SOx compounds from burning of gasoline and diesel have become global serious problems in the 21th century.Therefore,conversion of biomass or biomass-derived platform compounds to value-added chemicals and the alternatives of fossil fuel are important.Biofuels have numerous advantages such as high thermal energy,low pollution emission and biodegradability,and they are the alternatives foe the fossil energy in some extent.Recently,the conversion of biomass-derived platform compounds to value-added chemicals and fuels have become a rapidly growing research area.The key scientific issue of the biofuel production is design and preparation of efficient,stable and environmentally friendly solid-acid catalysts to overcome the disadvantages of conventionally homogeneous catalysts,such as equipment corrosion,environmental pollution and high treatment cost.In this paper,a series of immobilized acidic ionic liquid catalysts with different morphologies have been developed for the preparation of novel,efficient,stable and reusable environment-friendly solid acid catalysts for biomass conversion.Carbon materials with low cost were selected as the supports of acidic ionic liquids,and nitrogen atoms were doped into the framework of the supports.At the same time,the morphology of the supports was well-adjusted.The nitrogen-doped carbon suppotrs were functionalized by acidic ionic liquids.Acidic ionic liquids with strong Br?nsted acidity were chemically bonded onto the supports,and therefore nitrogen-doped carbon-based acidic ionic liquids with rod-like,hollow spherical and sea urchin spherical nanostructures were obtained.The morphology,structure,porosity properties and Br?nsted acidity of the catalysts were well-characterized by TEM,SEM,nitrogen gas porosimetry measurement,XRD,Raman scattering spectroscopy,FT-IR,XPS and potentiometric titration.Subsequently,the heterogeneous acid catalytic performances of the above newly prepared insoluable acidic ionic liquids were systematically evaluated by the reactions including esterification of glycerol to glycerides,selective alcoholysis of fructose to5-ethoxy methyl furfural?5-EMF?and ethyl levulinate?EL?,esterification of palmitic acid to palmitic acid methyl ester and esterification of benzyl alcohol with acetic acid to benzyl acetate for upgrading crude biofuels.The relationship between the Br?nsted acidity,morphology and porosity properties and the catalytic activity of the catalysts was revealed.Finally,the reusability of the catalyst was evaluated.The specific research contents are as follows.1.A series of rod-like nitrogen-containing carbon-based sulfonic acid functionalized ionic liquids,[PrSO3HN][SO3CF3]/C,with tunable Br?nsted acid site densities(1620-2304?eq g^-1)and diameters?10-200 nm?were fabricated by quaternary ammonization of hydrothermally prepared nitrogen-containing carbon nanorods with 1,3-propanesultone followed by anion exchange with trifluoromethanesulonic acid.The as-prepared[PrSO₃HN][SO₃CF₃]/Cs nanorods were applied in the selective esterification of glycerol with acetic acid or lauric acid to TAG or MLG and DLG.The results indicate that by the combination of the advantages such as high density of super strong Br?nsted acid sites,hydrophilic surface and perfect rodlike nanostructure,the[PrSO₃HN][SO₃CF₃]/Cs exhibited excellent catalytic activity in the target reactions.For the selective esterification of glycerol with acetic acid,the highest yield of TAG reaches 74.8%,and in the selective esterification of glycerol with lauric acid,the highest total yield of MLG and DLG reaches91.4%.Moreover,the[PrSO₃HN][SO₃CF₃]/Cs can be reused three times without catalytic activity loss.2.Nitrogen-doped carbon-based acidic ionic liquid hollow nanospheres,[C₃N][SO₃CF₃]-HCSs?C₃=PrSO₃H?,with different particle sizes?100-900 nm?and shell thicknesses?5-25 nm?as well as interesting morphology-dependent porosity properties were successfully prepared via quaternary ammonization of nitrogen atoms of hollow nitrogen-doped carbon nanospheres by 1,3-propane sultone followed by anion exchange with trifluoromethanesulonic acid.The[C₃N][SO₃CF₃]-HCSs were applied in selective conversion of fructose?FOS?to promising fuel blends,5-ethoxymethylfurfural?5-EMF?and ethyl levulinate?EL?.It showed the[C₃N][SO₃CF₃]-HCSs exhibited high total yields of5-EMF and EL?higher than 90%?,regardless of their particle size and shell thickness,attributed to extremely high selectivity to both compounds,and thereby,few side products including soluble oligomers and humins were produced.Additionally,the product distribution strongly depended on the morphology and porosity properties of the[C3N][SO3CF3]-HCSs.[C3N][SO3CF3]-HCSs-1 with the smallest particle size,thinnest shell,and largest BET surface area possessed the highest EL yield?89.7%?,while[C3N][SO3CF3]-HCSs-4 with the smallest particle size,thickest shell,and smallest BET surface area gave rise to the highest 5-EMF yield?67.2%?.More importantly,the[C₃N][SO₃CF₃]-HCSs can be reused five times without changes in catalytic activity,Br?nsted acid nature,morphology,and porosity properties.3.A series of urchin-like nitrogen-doped carbon-based acidic ionic liquid,[C₃N][SO₃CF₃]-UlCs,with different particle sizes?200-600 nm?and degree of density composite folds as well as interesting morphology-dependent porosity properties were successfully prepared via quaternary ammonization of nitrogen atoms of urchin-like nitrogen-doped carbon supports by 1,3-propane sultone followed by anion exchange with trifluoromethanesulonic acid.The[C₃N][SO₃CF₃]-UlCs showed an excellent activity in the three esterification reactions including esterification of glycerol with acetic acid,esterification of palmitic acid with methanol and esterification of benzyl alcohol with acetic acid,the corresponding yields of TAG,methyl palmitate and benzyl acetate were 75.9%,100%and 100%.Moreover,the[C₃N][SO₃CF₃]-UlCs can be reused for five times without catalytic activity loss in the aforementioned three esterification reactions.