Designation Of Novel Polyoxometalate And Bimetallic Catalysts In Catalytic Transformation Of Biomass

The depletion of fossil fuel resources and the resulting adverse effects on the global environment and climate are of major academic,economic and political concern worldwide.As supplies of fossil fuels and related petrochemicals may soon be limited,alternative solutions are sought.One alternative is to develop a series of novel chemical processes based on renewable feedstocks,typically biomass and biomass-derived chemicals.Biomass is a sustainable and green feedstock for the production of fuels and fine chemicals with net zero carbon emission.Among them,carbohydrates?namely starch and lignocellulose?are the primary energy-storage molecules.Carbohydrates are widely available in the nature world,it can be transformed into a lot of important platform moleculars and value-added chemicals.Polyoxometalates?POMs?have an unmatched range of physical and chemical properties which arise from their seemingly endless variety of molecular structures.The diverse range of functionalities displayed by this large class of molecules can be exploited in a variety of applications.Catalysis was one of the first applications of POMs and is still the most common.POMs exhibit very strong Bronsted acidity,making them suitable for various acidic reactions,such as esterication,transesterication,hydrolysis,Friedel-Crafts alkylation and acylation,and Beck-mann rearrangement.POMs are well known to have fast and reversible multi-electron redox behaviors under mild conditions,which makes them promising candidate catalysts for the oxidation of alkanes,aromatics,olefins,alcohol,etc.The use of bimetallic catalysts is a promising option for biomass feedstock upgrading,as the interaction between metals can modify the surface properties of the catalyst.These changes can significantly improve the catalytic activity,modify the selectivity to the desired product,and increase the catalyst stability in presence of biomass-derived impurities and more severe reaction conditions.New bimetallic catalysts need to be optimized specifically for each reaction ensuring high reaction rates,high selectivity,and yields that lead to effective purification steps.Based on the above discussion,we designed and prepared three different kinds of novel catalysts targeting to convertion of biomass derivertives to importment platform moleculars and value-added chemicals,including POM-based catalyst,bifunctional bimetallic catalyst and POM-based bimetallic catalyst.The specific research contents are as follows:?1?In chapter 2,the Ch₅PMo₁₀V₂O₄₀ catalyst has been synthesized using choline chloride and H₅ PMo₁₀V₂O₄₀ as building blocks,which resulted in nonconventional POMs-IL in solid state at room temperature.This POM-IL catalyst exhibited higher efficiency in catalytic oxidation of starch with H₂O₂ with a degree of oxidation of 0.59 molCO₂H per 100 g under the mild conditions,which was comparable to traditional homogeneous catalyst FeS04.It was used as a "temperature controlled self-separation catalyst" for oxidation of starch due to its property of switching from homogeneous to heterogeneous system,which made the recovery and reusability quite convenient.?2?In chapter 3,we prepared a crystal isopolyoxovanadate catalyst Na4Co?H₂O?6VO₁₀O₂₈·18H₂O(CoV₁₀),sucessfully,and demonstrated its superior catalytic activity over other methods on starch oxidation for its advantage of activating oxygen,which make it a possible to aerobic oxidation of starch.The best reaction conditons were:pH = 6;temperature,50?;reaction time,8 h;and catalyst amount,8 mg.Therefore,this work considerably importantand have a far-reaching impact on modifying refractory biomass,since there is hardly any successful examples at present.?3?In chapter 4,bimetallic RhRe catalysts with 4 wt%Rh and Rh:Re atomic ratio of 1:05 supported on Vulcan XC-72?VXC?and Norit Darco 12x40?NDC?were characterized and their activity was studied for hydrogenolysis of THP-2M.NDC has?3 times higher BET surface area than VXC?BET surface area of 671 m2·g-1 vs 237 m2·g-1?and has?15 times higher water adsorption capacity than VXC?17.5 mmol·g-1 vs 1.2 mmol·g-1?.XPS revealed 20 time greater presence of oxygen on the NDC surface as compared to the surface of VXC.The RhRe/NDC catalyst showed 2 orders of magnitude lower activity and 10 times lower 1,6-HDO selectivity than RhRe/VXC for hydrogenolysis of THP-2M.?4?In chapter 5,we firstly synthesized the Cs_0.5H_0.5PW₁₂O₄₀?CsPW?as support,then using the incipent wetness impregnation method prepared the Rh/CsPW?Re/CsPW ? Rh-Re/CsPW catalyst.These catalysts were applied in the conversion of THFDM to 1,6-hexanediol.The best reaction conditons were 200 ?,4 h,20 bar H₂,and 200 mg catalyst.At the prevailing reaction conditions,the conversion of THFDM were 38%,and the selectivity of 1,6-HDO and THP-2M were respectively 42%and 41%,which is comparable to the best literature report using RhRe/SiO2 and Nafion SAC-13 as mixture catalyst.The key element of the high catalytic activity of this catalyst lies in the interaction between the Rh and Re to form the core-shell structure.