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Investigation Of Polyoxometalates Containing Mo And V On Catalyzing Oxidation Of Starch With H2O2/O2

Posted on:2018-03-26Degree:MasterType:Thesis
Country:ChinaCandidate:T JiaFull Text:PDF
GTID:2321330515968883Subject:Inorganic Chemistry
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Biomass is the most abundant and renewable carbon source on earth.Bio-refinery shows a big possibility of getting high value-added chemicals from common biomass,which has been to some degree successful.Chemical modification is an important part of it.Starch is one of the most sustainable and available biomass.The hydrophilic OH groups of the unmodified starch molecule tend to form intermolecular and intramolecular hydrogen bonds limiting the usefulness of the material for certain applications.Functionalization of starch in oxidation,esterification and etherification could adjust its structure and thus it can be used for high volume applications in industries.Meanwhile,the strategies of oxidation modifying are under the way.Fenton is the major way in industrial processes,which possess many drawbacks such as the contamination of products and restriction of pH.Green and environmental-friendly solutions are the key point for achieving modified.Normal oxidation agents like hydrogen peroxide give rise to high-cost procedures and low-quality products.Oxygen is said to be an ideal oxidant and utilizing oxygen in place of hydrogen peroxide is also the main target in all oxidation reactions.Polyoxometalates(POMs)are a subset of metal oxides with unique physical and chemical properties.Owing to the varieties of acid strength and redox potential,they have been using in catalysis,medicine and material science.POMs can be used as acid catalysts,oxidation catalysts and photo catalysts,and all of them show high stability and reactivity.Many studies have revealed that POMs are useful and suitable catalysts for selective transformation of biomass,and POMs-based oxidation of biomass is more and more attractive.Based on these,we screened three types of polyoxometalates and performed the oxidation of starch with the aid of hydrogen peroxide and oxygen.The optimizations of these systems were also discussed.1.K3H3V10O28 was synthesized and acted as catalyst in the oxidation of native starch and raw cornstarch.It showed good efficiency with both of the two substrates.The best result for native starch is 0.683 mol/100 g under the condition of starch 1 g,80 oC,4.5 mL hydrogen peroxide,1.5 mL water,and catalyst amount of 0.03 wt% for 10 h.The best results for corn starch is 0.543 mol/100 g under the condition of starch 1 g,80 oC,4.5 mL hydrogen peroxide,1.5 mL water,catalyst amount of 0.06 wt% for 10 h.2.B-type Anderson [CoMo6O24H6]3-anion was chosen and used in the oxygen-presence oxidation of starch.The homogeneous and heterogeneous effects of starch were also tested.The homogeneous catalyst(NH4)3[CoMo6O24H6] gave carboxyl content of 1.139 COOH/100 GU,carbonyl content of 2.61 CO/100 GU,solid starch yield of 73.6% at the condition of 10 h,50 oC,1.5 g starch,0.10 mmol catalyst.The heterogeneous catalyst(CTA)3[CoMo6O24H6] gave carboxyl content of 0.072 COOH/100 GU,carbonyl content of 1.58 CO/100 GU,solid starch yield of 94.9% under the condition of 10 h,80 oC,1.5 g starch,0.10 mmol catalyst.This is the first work of oxidizing starch using B-Anderson polyoxometalates and the changes occurred on starch granules during the modification process were recorded by XRD and SEM.3.We conducted the modification with one A-type Anderson polyoxometalate anion [IMo6O24]5-under both the homogeneous and heterogeneous conditions.For the homogeneous system,the best results were carboxyl content,0.956 COOH/100 GU,carbonyl content,3.394 CO/100 GU,solid starch yield,79% when 8 h,50 oC,1.5 g starch,0.19 mmol Na5[IMo6O24] were chosen.For the heterogeneous counterpart,carboxyl content of 0.106 COOH/100 GU,carbonyl content of 1.41 CO/100 GU,solid starch yield of 95.5% were got under the condition of 10 h,95 oC,1.5 g starch,0.19 mmol(CTA)5[IMo6O24].This is the first example of homogeneous and heterogeneous A-type Anderson polyoxometalates catalyst for starch oxidation.
Keywords/Search Tags:Polyoxometalates(POMs), Oxidation, Starch, O2, H2O2, Oxidized starch
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