Design Of Supported Br?nsted Acidic Ionic Liquid And Studies On Their Catalytic Performance

Catalytic conversion of renewable biomass resources into high value-added organicchemicals and high-quality fuels（or fuel additives）is one of the most important ways to effectively reduce the dependence on fossil fuels and realize the aim of Peak carbon dioxide emission and Carbon neutralization（refers to the direct and indirect emission of carbon dioxide by countries,regions,companies,groups,and individuals within a certain period of time,which are offset by the carbon dioxide absorbed by afforestation and other methods,and achieves net zero carbon dioxide emissions）.Transformation of the important biomass-derived platform compounds such as 5-hydroxymethylfurfural（HMF）,fructose and xylose to high value-added organic chemicals and oxygenated fuel additives has become a research hotspot.One of the key scientific issues in this subject 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 and environmental pollution.As new green acid catalysts with superstrong Br?nsted acidity,low volatility and environmentally benign,Br?nsted acidic ionic liquids（BAILs）play an important role in the conversion of biomass resources into high value-added organic chemicals and high-quality fuels.However,the inherent high viscosity and low diffusivity of ionic liquids not only increase the diffusion and mass transfer resistance of reactants and products but also bring difficulties of the separation,recovery and recycling.Chemical immobilization of BAILs on porous supports can effectively overcome the above problems.In this master’s thesis,a series of the supported BAILs catalysts with different morphologies were developed,which included BAILs functionalized dendritic fibrous nanosilica spheres and three-dimensional coral-like covalent organic polymers.By the combination of the superstrong Br?nsted acidity and unique nanostructure,the activity and selectivity of as-prepared supported BAILs are expected to be improved remarkably in catalytic conversion of biomass.The morphology,composition and structure,porosity properties as well as Br?nsted acid nature of as-prepared supported BAILs were well-characterized by SEM and element mapping images,TEM,nitrogen porosimetry measurement,XPS,²⁹Si MAS NMR,¹³C CP-MAS NMR,FT-IR,nonaqueous potentiometric titration and acid-base titration.Meanwhile,the catalytic activity,selectivity,reusability and reaction mechanism of as-prepared supported BAILs were studied.The relationship between the Br?nsted acid nature,morphology and porosity properties and the catalytic activity and selectivity of the catalysts was revealed.The specific contents are as follows.1.A CPB reverse micelle-directed co-condensation route followed by successively chemical modification was designed for the preparation of novel supported BAIL catalysts,[C₃Pr Im][SO₃CF₃]?DFNS,with fantastic monodispersed dendritic fibrous spherical nanostructures,and the particle diameter,fiber thickness and fiber density of the catalysts can be well-regulated by changing the molar composition of the starting materials.By the combination of superstrong Br?nsted acidity and open three-dimensional dendritic fibrous nanostructures,the[C₃Pr Im][SO₃CF₃]?DFNS show extremely high catalytic activity in transformation of HMF to ethyl levulinate（EL）in ethanol media;meanwhile,the selectivity of the catalysts to EL is remarkably affected by fiber thickness and fiber density.The[C₃Pr Im][SO₃CF₃]?DFNS-1 catalyst with the thinnest fiber thickness and considerably high fiber density shows the highest selectivity to EL（93.0%at 120 ^oC and 180 min）.The[C₃Pr Im][SO₃CF₃]-DFNS catalysts also showed good reusability,and they can be reused at least for five times without obvious changes of the conversion of HMF,total selectivity,morphology and chemical structure of the incorporated[C₃Pr Im][SO₃CF₃]units,originating from covalent bonding of the[C₃Pr Im][SO₃CF₃]units within DFNS support and the stabilization of the wrinkled fibers of the support to the[C₃Pr Im][SO₃CF₃]sites.2.A series of three-dimensional coral-like BAIL functionalized covalent organic polymer（COP）catalysts,[C_3/4N][OTf]?PA?MA（C₃=Pr SO₃,C₄=Bu SO₃,[OTf]=CF₃SO₃）,were prepared via hydrothermal treatment technique followed by quaternary ammonization and anion exchange.The Br?nsted acid site density of the[C₃N][OTf]?PA?MA were adjusted by changing the concentrations of 1,3-propanesultone（and CF₃SO₃H）.In order to study the influence of cation of BAILs on the catalytic activity,[C₄N][OTf]?PA?MA was also prepared.The heterogeneous acid catalytic properties of as-prepared[C_3/4N][OTf]?PA?MA catalysts were systematically evaluated in the reactions of microwave-assisted dehydration of fructose/xylose to HMF/furfural.It shows that the[C₃N][OTf]?PA?MA-1 catalyst with the highest Br?nsted acid site density exhibited the highest catalytic activity and selectivity in both target reactions.For examples,under the conditions of 120 ^oC,microwave irradiation 30 min,the yield of furfural reached 85.2%;under the conditions of 160 ^oC,microwave irradiation 30min,the yield of HMF reached 51.8%.The excellent heterogeneous acid catalytic activity of the[C_3/4N][OTf]?PA?MA is attributed to the combination of the advantages of the superstrong Br?nsted acidity and high acid site density,three-dimensional porous coral-like nanostructure and microwave assistance.More importantly,COP structures possess excellent chemical and hydrothermal stabilities;meanwhile,the chemical interactions between the–[Pr/Bu SO₃H][OTf]units and nitrogen-containing carbon framework can avoid acid sites leaching.Both of the advantages ensured excellent reusability of the[C_3/4N][OTf]?PA?MA catalysts.