Studies On The Catalytic Hydrogenation Of Cellulose And Platform Molecule

Excessive exploitation of traditional fossil resources leads to the depletion of fossil resources,and the excessive use of fossil resources also causes serious environmental pollution problems,such as the greenhouse effect and the emission of environmental pollutants(PM2.5,floating carbon,hydrocarbons,carbon monoxide,nitrogen oxides,sulfide,etc.).In order to reduce industrial development's heavy reliance on fossil resources and reduce the pollution of the environment pressure,the government and organizations in all countries of the world want to develop green clean energy to partially or completely replace fossil energy.Biomass is a supramolecular carbohydrate formed by the polymerization of photosynthesis products,which is the only renewable organic carbon resources in nature.Biomass resources in nature are abundant,widely distributed,green,clean and recyclable,and become potential resources to replace non-renewable fossil resources.Using biomass resources as green raw materials,fuel and high value-added chemicals can be produced by conversion in a variety of chemical ways.Cellulose is the most abundant component in the three components of lignocellulosic biomass resources(cellulose,hemicellulose and lignin).The structure of cellulose is a biopolymer connected by ?-1,4-glucoside bonds and presents a netlike model structure with high crystallinity.The polymer structure of cellulose contains a large number of hydroxyl functional groups,and these hydroxyl functional groups have strong hydrogen bonding between them.The intramolecular and intermolecular hydrogen bonding forces make them form a rigid three-dimensional crystalline network.Due to the rigidity and complexity of cellulose structure,downstream conversion of cellulose is very difficult and product distribution is complex.In response to the above problems,we designed and developed multi-functional catalysts to achieve efficient depolymerization of cellulose and selective catalytic hydrogenation to produce relatively single fuel molecules(ethanol)or high value-added chemicals of diols(ethylene glycol and propylene glycol).At the same time,the functional catalyst can also realize the selective catalytic hydrogenation of cellulose downstream platform molecule levulinic acid(ester)to produce high value-added chemicals.The chapter 1 introduces the importance of biomass processing technology and biomass resource conversion and utilization as well as the current research status.In particular,there are many ways of conversion of cellulose components to the downstream by selective catalytic hydrogenation and detailed research status.The chapter 2 briefly introduces the development status and research significance of bioethanol,and a multi-functional Ru-WOx/HZSM-5 catalyst has been developed and designed to catalyze the efficient hydrogenation of cellulosic biomass in a one-pot to produce fuel molecular ethanol with high selectivity.Characterization studies revealed a highly dispersed Ru3W17 alloy along with moderate acid sites that displayed a synergistic catalytic effect.The catalytic system can be regulated to promote hydrolysis,retro-aldol condensation,dehydration and hydrogenation to achieve ethanol and suppress side reactions such as oligomerization to form humins.At the same time,the combination of two-step temperature rise method and addition of Ru/WOx catalyst to catalyze retro-aldol condensation of glucose effectively increased the ethanol concentration.The chapter 3 introduces the application of diols(glycol and 1,2-propanediol)and the research status of preparation of diols from biomass cellulose.Finally,the conversion of cellulose into ethylene glycol and 1,2-propanediol by one-pot method with high selectivity and yield was realized by developing weakly basic catalytic system(Co/CeOx).Characterization and reaction tests confirmed that the interaction between well dispersed Co and CeOx supports lead to Con+-Ox-Ce3+ acid-base pairing that constitute the main catalytic sites.Overall,the catalyst was found to be slightly basic,which resulted in low sugar concentrations due to the moderate suppression of cellulose hydrolysis,the rate-determining step.The weakly basic environment and minimal accumulation of sugars efficiently hindered resinification to humins.The delicately controlled acid-base property of the catalyst ensures a particular balance across the reaction steps,namely,hydrolysis,retro-aldol condensation,isomerization,and hydrogenation.This is the first reported weakly basic catalytic system for cellulose depolymerization.The chapter 4 introduces the conversion of fructose to 1,2-propylene glycol(PG)is an important process from cellulosic biomass to high-value added chemicals.Herein,Ru-WOx/HAP catalyst was employed for this reaction and reached up to 91.3%yield of PG at 180?,1 MPa H2 and 8 h in water.On this catalyst,Ru and WOx were highly dispersed on HAP support and they interacted with each other to form a special catalytic center.The lack of isolated Ru or RuW alloy site led to a moderate activity for hydrogeno lysis and hindered the further conversion of PG to propanol.The weak basic HAP support efficiently prevented the humin formation.This precisely controlled catalyst has potential in green PG production.The chapter 5 introduces the important uses of levulinic acid(ester)and the hydrogenation product of y-valerolactone.Gamma-valerolactone(GVL)has been identified as a sustainable high-value platform molecular for the production of fuels and carbon-based chemicals.In this work,a series of activated carbon supported low-cost bimetallic Ni-Fe catalysts(Ni-Fe/AC)with different molar content of Fe species were prepared by using co-precipitation method for the liquid phase hydrogenation of ethyl levulinate(EL)to produce y-valerolactone.The Ni-Fe0.5/AC exhibited the highest activity among the bimetallic or monometallic catalysts under mild reaction conditions.Based on the structure and activity relationship study,the formation of highly dispersed Ni-Fe alloy structure and the co-presented FeOx nanoparticles could be responsible for the high catalytic hydrogenation activity.In the chapter 6.Summary and prospect.This thesis mainly of introduces studies on the catalytic hydrogenation of cellulose and the downstream platform molecules.Various multifunctional catalysts have been developed and designed to selectively catalyze cellulose and platform molecules to produce fuel molecules and high value-added chemicals.The structure-activity relationship between each catalytic system and the reaction are studied in details,and the future prospects of the hydrogenation of biomass and the development of multifunctional catalysts are also discussed.