Design,Synthesis And Catalytic Oxidation Properties Of Polyoxometalates Catalysts

Starch as one of the most renewable nature biopolymers, because of its relativelyinexpensive and abundant availability, has proven to be an important subject for theresearch of materials from biomass. As the rapid development of science technology,the intrinsic properties of native starch, like the structure and performance, hadsuffered a great limit in the application of modern manufacture. As a result,researchers of different countries launched the deep processing technology of starchmodification, which based on the structure and physicochemical properties of nativestarch. Oxidized starch is an important branch of modified starch. It owns much moreextensive application in paper, textile, food and many other modern industrial areasbecause of its quality characteristics, such as easy pasting, low paste viscosity, highthermal stability, high transparency, good film and good freeze-thaw resistance.Consequently, finding an economical and efficient method for the starch oxidation hasa potential prospect. Polyoxometalate is attracting more and more attention because ofits unique catalytic activity such as it can be used as an acid catalyst, an oxidationcatalyst or a bifunctional catalyst in the homogeneous and heterogeneous systems.Among the various oxidant, hydrogen peroxide with the advantages of safe, clean,water as the only product after the reaction is an ideal environmentally friendlyoxidant and plays an extensive and important role in the in the field of oxidation. Thepresent paper designs polyoxometalae as the oxidation catalyst and the hydrogenperoxide as the oxidant to prepare the oxidized starch under a neutral and mildcondition. This work solves the drawbacks in the traditional oxidations of starch, suchas the waste of large quantities of water and oxidant, environmental problemsdeduced from the oxidant unable to be retrieved in the homogenous system. It is anenvironmental friendly catalyst for the starch oxidation. The main results of this workare as follows:1. A series of insoluble cesium salts of10-molybdo-2-vanadophosphoric acids,Cs_xH_5-xPMo₁₀V₂O₄₀（x=0.5,1.0,1.5,2.0,2.5,3.0,3.5,4.0,4.5,5.0） wereprecipitated and characterized by Elemental analysis, Fourier transform infraredspectroscopy （FT-IR）, X-ray diffraction （XRD）, nitrogen adsorption-desorptionisotherm, scanning electron microscopy （SEM） and acid content. The catalytic activity and the effect of cellulose amount of the catalysts were evaluated for theoxidation of starch. A study to optimize the reaction conditions was studied. Theresults showed that the optimal conditions were: the best catalyst Cs₃H₂PMo₁₀V₂O₄₀,1g of starch,2mL of distilled water, reaction temperature70C, reaction time10h,oxidant amount4mL, catalyst amount4mg, the highest content of carboxyl groupcould0.59mol/100g and the catalytic activity of catalyst was still very good after sixtimes.2. A series of silver and ammonium salts of10-molybdo-2-vanadophosphoricacids, Ag_x（NH₄）_5-xPMo₁₀V₂O₄₀（x=0,0.5,1.0,1.5,2.0,2.5,3.0,3.5,4.0,4.5,5.0）were precipitated and characterized by Elemental analysis, Fourier transform infraredspectroscopy （FT-IR）, X-ray diffraction （XRD）, nitrogen adsorption-desorptionisotherm and scanning electron microscopy （SEM）. The catalytic activity and theeffect of silver and ammonium amount of the catalysts were evaluated for theoxidation of starch. A study to optimize the reaction conditions was studied. Theresults showed that the optimal conditions were: the best catalystAg_3.5（NH₄）_1.5PMo₁₀V₂O₄₀,1g of starch,2mL of distilled water, reaction temperature80C, reaction time10h, oxidant amount4mL, catalyst amount4mg, the highestcontent of carboxyl group could0.62mol/100g and the catalytic activity of catalystwas still very good after six times.