Studies On Oxidation Performance And Mechanism Of Iodide Ions Catalyzed By Mo-containing Polymetallic Oxygen Clusters

Iodine is one of the essential trace elements in human body,and is also the basic chemical raw material for the manufacture of organic or inorganic iodine.Iodine chemical products are widely used in food,pharmaceuticals,industry,agriculture,national defense technology and other industries.Traditional catalytic oxidation methods for iodine recovery have the following problems: low catalytic efficiency,catalyst limited by reaction pH value,iodine peroxidation,and contamination caused by the introduction of new ions into the reaction system.Therefore,the development of environmentally friendly and efficient catalysts is the development trend of iodine industry.Polyoxometalates?POMs?are efficient and environmentally friendly catalysts.Compared with traditional catalysts,POMs exhibits higher catalytic activity,selectivity,thermodynamic stability,mild reaction conditions and noncorrosive behavior.In recent years,it has attracted much attention in the field of materials and catalysis.In this article,a series of molybdenum-containing polymetallate catalysts with different central atoms,coordination atoms and configurations were synthesized by different synthesis methods to study the catalytic performance of iodine ion oxidation.The materials were characterized and evaluated by means of elemental analysis?ICP-AES?,Fourier infrared?FI-IR?,X-ray powder diffraction?XRD?,solid ultraviolet diffuse reflection?UV-Vis-DRS?,iodine ion selective electrode and other means,and the influencing factors of catalyst catalytic activity as well as the mechanism of iodine ion oxidation by hydrogen peroxide and the mechanism of catalytic reaction were systematically investigated.The main research contents and conclusions are as follows:1.A series of molybdenum-containing polyoxometalates with different central atoms?P,Si,Ge?and different transition metals?Ni,Co,Mn,Zn,Cu,Fe,Ti?have been synthesized by different synthetic methods.The Keggin type polyoxometalates are used as catalysts to catalyze the oxidation of iodine ions by hydrogen peroxide.The experimental results showed that the series of catalysts all had good catalytic activity,and the conversion rate of iodine ion reached 96.3%.Among them,K-PMo₁₂had the best catalytic activity and the best reaction conditions: that is,in the system with a total volume of 40 ml,when C?I^-?=0.01mol/L,n?H₂O₂?/n?I^-?=0.7,n(K-PMo₁₂)=0.6mmol,T=45?,pH=1.2,the catalytic reaction rate was 1.7224×10^-4mol·L^-1s^-1,can realize the iodine ion almost 100% of the conversion.By simulating actual industrial production and introducing counterions into the catalytic reaction system,it is found that the counteracting ions introduced from the outside will not destroy the catalytic reaction system,but have a certain positive effect on the catalytic reaction.In the catalytic reaction system,the catalyst itself will not generate oxidation and peroxidation to iodine ions and iodine simple substance.2.Different transition metals?Ni,Co,Mn,Zn,Cu,Cr?were synthesized by solvent method to replace Waugh type molybdenum-containing polymetallic oxalate.The results showed that the order of catalytic oxidation capacity of different transition metal ion centers replacing Waugh type molybdenum-containing polymetallic oxonate catalysts was: Cu>Zn>Mn>Ni>Cr>Co.The catalytic activity of Waugh type molybdenum-containing polymetallic oxalate catalyst replaced by Cu center was better.The optimal reaction conditions were as follows: under the condition that n?W-CuMo₉?=0.9mmol,C?I^-?=0.01mol/L,n?H₂O₂?/n?I^-?=0.8,pH=1.2,T=50?,and the total volume remained unchanged at 40 mL,the catalytic reaction rate was1.7839×10^-4mol·L^-1·s^-1.The effects of external counteracting ions on the catalytic reactivity were investigated and it was found that counteracting ions would not destroy the catalytic reaction system but would have some positive effects on the catalytic reaction.In the preliminary experiment,it was found that the catalyst did not produce oxidation and peroxidation of iodide ions and iodide elements.3.The catalytic activity of the Ni-centered Waugh-type and Anderson-type mo-containing polymetallic oxonate catalysts in iodide oxidation was studied.According to the test of catalytic activity and the calculation of quantum chemistry,the oxidation capacity and catalytic activity have the same order: W-NiMo₉>A-NiMo₆.The catalytic reaction of both catalysts conforms to the quasi-first-order kinetics.According to the Mulliken distribution data and frontier orbital energy levels,it is found that Ni and the oxygen atoms connected with Ni and theterminal oxygen have the ability to participate in chemical reactions and can be used as active centers in catalytic reactions.4.The quantum chemistry was used to simulate the reaction of hydrogen peroxide to oxidize iodide ion.Through the simulation and experiment test found by the free radical and free radical reaction iodine elemental will have oxygen to produce at the same time,put forward possible catalytic reaction mechanism,catalyst itself structure due to Mo-O bond strength is weak,easy to fracture in Mo generated space with the substrate forming reaction intermediates or active substances,thus achieve the catalytic role.