Design Of Porous Catalysts And Study On The Preparation Of 5-hydroxymethylfurfural From Carbohydrates Biomass Conversion

Employing the most abundant and renewable carbohydrates as raw material for production of biomass-based chemicals will benefit relieving the currently serious energy crisis and environmental pollution. 5-Hydroxymethylfurfural (5-HMF) is a biomass-based platform compound, which contains active aldehyde groups, hydroxyl and furan ring, and has been considered as key intermediate for biomass chemical and petroleum chemistry. Various kinds of products can be obtained from 5-HMF transformation. Recently, the construction of catalytic system with high efficient is an important work for enhancing the production and industrial application of 5-HMF. And design of catalyst and solvent system has been considered as two main factors for carbohydrates conversion to 5-HMF. Recently, due to its low density, large specific surface area, high porosity, low corrosion of equipment, easy separation and less industrial wastewater, porous solid catalyst has been aroused wide attention.In this dissertation, the key factors for effecting carbohydrates conversion to 5-HMF has been investigated intensively. And based on the results, a series of porous solid catalysts were prepared. Taking the synthesis method and performance optimization for catalyst as key points,through adjusting catalysts pore structure, increasing the active sites, and controlling the active sites species, the 5-HMF yield can be effectively enhanced. By a variety of characterizations, the morphology, structure, chemical composition, acid-base intensity, thermostability and surface property of as-prepared catalysts were investigated. The catalytic performance and influence factor of porous solid catalyst were investigated through carbohydrates conversion to 5-HMF in the presence of various solvents. And the conclusion has also been proposed, correspondingly.The main research work included the following items:1. Mesoporous molecular sieve of SBA-15 supported solid catalysts for catalytic conversion of carbohydrates to 5-HMF(1) Sulfated zirconia (SZ) monolayers and ceria were successfully incorporated into mesoporous SBA-15 via layer-by-layer grafting and wet impregnation methods. The supported SZ afforded the catalysts with high Br(?)nsted/Lewis acid strength and relatively low base strength, and the 2SZ@SBA-15 catalysts exhibited optimum surface acidity and balance of Br(?)nsted/Lewis acidity. The base strength of catalysts was significantly enhanced by introducing highly dispersed ceria onto the network of 2SZ@SBA-15, and the 5 wt%CeO2-2SZ@SBA-15 catalysts displayed attractive acid and base strength. The catalytic activities of the CeO2-2SZ@SBA-15 catalysts were evaluated through the conversion of glucose to 5-Hydroxymethylfurfural (5-HMF) in an iPrOH/DMSO solvent mixture. Co-existed base and Lewis acid sites in CeO2-2SZ@SBA-15 catalysts was found to promote glucose isomerization to fructose, and Bronsted acid sites direct the dehydration of reactively formed fructose to 5-HMF.Highest 5-HMF yield of 66.5% and selectivity of 70.8% were obtained in a 90 vol%isopropanol-mediated DMSO solvent. The developed reaction system in this paper avoided the use of large amount of environmentally hazardous solvent.(2) Fe3O4 nanoparticles encapsulated SBA-15 (i.e.,Fe3O4@SBA-15) with appropriate pore size was synthesized and utilized as magnetic scaffolds for the immobilization of cellulose to synthesize biocatalyst. Sulfated zirconium dioxide (SZ) conformed monolayers and ceria were grafted on SBA-15 template to create thermally robust mesoporous chemical catalysts with tunable Br(?)nsted/Lewis acid and base sites. Catalytic performances of biocatalyst and chemical catalyst were explored in the aqueous phase conversion of cellulose-to-glucose, and in the iPrOH/water solvent conversion of glucose to 5-HMF conversion, respectively. And a novel route to deconstruct cellulose into 5-hydroxymethylfurfural (5-HMF) by integrating enzymatic and chemical cascade reactions can be realized. After the optimization of reaction conditions, a sequential cellulose-to-glucose and glucose-to-HMF conversion were carried out, and 45.6%5-HMF yield can be obtained.2. Porous solid catalysts with acid-base bi-functional sites for one-pot catalytic conversion of carbohydrates to 5-HMF(1) Acid (-SO3H), base (-NH2) and both acid-base (-SO3H and -NH2) functional groups were grafted on 2SZ@SBA-15 to synthesize 2SZ@SBA-15-SO3H,2SZ@SBA-15-NH2 and 2SZ@SBA-15-SO3H-NH2, respectively. The catalytic activities of the SBA-15 supported catalysts were evaluated toward the cellulose conversion to 5-HMF in an ILs-based system,which experienced a series of sequential processes involving a decomposition step to glucose, an isomerization reaction to fructose and the fructose triple dehydration step with three molecules of water to 5-HMF. With the goal of understanding the role of catalysts in the sequential processes for cellulose to 5-HMF conversion, the synthesized catalysts possessing different Br(?)nsted/Lewis acidity and basicity were applied in the reactions using cellulose, glucose and fructose as starting materials. Results of catalytic experiments indicated the integration of required acid and base characters in one catalyst has advantageous property for cooperative catalysis of one-pot cellulose to 5-HMF. Highest 5-HMF yield of 42.2% and selectivity of 54.0%can be obtained from cellulose under the optimal conditions.(2) High internal phase emulsions (HIPEs) templating methodology, subsequent ion-exchange, and the surface grafting technique were combined to synthesize macroporous,acid-base bifunctional, and superhydrophobic polymeric solid catalyst for the production of 5-HMF from cellulose in a one-pot manner. Results of characterization demonstrated that the as-prepared catalyst possessed average void diameter at 12.5 ?m, interconnecting pore diameter at 2.8?m, contact angle at 150°, acid strength at 3.034 mmol g-1 and base strength at 1.379 mmol g-1, respectively. By simply varying the parameters of HIPEs templates (i.e., the volume fraction of the internal phase and surfactant concentration), the molar ratio between acid/base monomer and the grafted amount of 1 -dodecanethiol, the pore structure, acid and base strengths,wettabilities of catalyst can be easily adjusted. Results of catalytic experiments involving cellulose-to-HMF conversion indicated that as-prepared catalyst can effectively improve the reaction rate, increase the HMF yield and prohibit the hydration of 5-HMF to by-products. And remarkable 5-HMF yield of 49.5% and selectivity of 55.9% can be obtained under the optimal conditions. Furthermore, catalyst can be easily recovered and reused at least five times without significant loss of catalytic activity.3. Pickering HIPEs template constructed porous solid catalysts for catalytic conversion of carbohydrates to 5-HMF(1) Stable water-in-oil (W/O) Pickering high internal phase emulsions (Pickering HIPEs)with an internal phase volume fraction of 84.8% were first stabilized by both the hydrophobic silica nanoparticles and span 80. Then, based on the obtained Pickering HIPEs, several macroporous polymerized solid acid (PDVB-SS-X-SO3H) were prepared by polymerizing divinyl benzene (DVB) and sodium p-styrenesulfonate (SS), and were subsequently combined with sulfonation in H2SO4. All the as-prepared PDVB-SS-X-SO3H possessed open-cell structure,interconnecting pores and strong acidity, and were adopted as catalysts to convert cellulose into 5-HMF in ILs solvents. Highest 5-HMF yield of 12.9% for PDVB-SS-O-SO3H, 29.6% for PDVB-SS-0.2-SO3H and 15.5% for PDVB-SS-0.6-SO3H were obtained under the optimal conditions, revealing that the pore sizes and strong acidic sites played a key role in cellulose conversion. Compared with other works, not very ideal yield of 5-HMF obtained in this work was mainly caused by the catalyst containing sole Bronsted acid sites, making the involving reaction steps cannot be processed smoothly.(2) Macroporous inorganic-organic hybrid polymers (MIPs) were prepared using versatile Pickering HIPEs templating to synthesize a novel catalyst for cellulose conversion. Upon the incomplete hydrothermal carbonization of MIPs and sulfonation with H2SO4, macroporous carbonaceous solid catalysts (MCSC) with hierarchical structures and Br(?)nsted-Lewis acid sites were obtained. The synthesized MCSC was found to be highly effective to produce 5-HMF in ionic liquids. Compared with traditional HIPEs template, using Pickering HIPEs template to synthesize porous solid catalyst can avoid using large amount of surfactant and organic phase.And the method developed in this work offers a new route for the synthesis of carbonaceous solid catalysts with hierarchical pore and multi-functional active sites.