| Iodine is an important chemical material,which is widely used in the fields of electronics,medicine and metallurgy.It is also a scarce resource in China.In recent years,it's self-sufficiency rate is only 16.7%,we need import about 83.3%iodine from Chile,Japan and other countries.Why we need to import such a large of iodine?The reason is that the amount of iodine,such as the associated iodine is large,the iodine content is very low,and the rate of iodine ions oxidized into iodine is very slow.We can use the catalyst to improve the rate of iodine ion oxidation to solve this problem.Polyoxometalates?POMs?is a new highly effective environmental catalyst with stable structure,acidic and redox properties,"quasi-liquid phase"behavior and unique coordination capability.Compared with the traditional catalysts,POMs exhibit higher catalytic activity,selectivity,thermodynamic stability and catalytic oxidation stability,which have been widely concerned in recent years.This application of POMs in inorganic solvents is limited because of its small specific surface area and soluble in inorganic solvents.Based on this,this paper uses the phosphorus molybdate?PMo?as catalyst to oxidize and load the iodine ions on the high specific surface area of the carrier,so that the catalyst can be reused repeatedly in inorganic solvents.At the same time,the properties of the reaction of the oxidation of iodine ions to iodine oxides by the supported polyoxometalates compounds were studied.The main contents and the conclusions are as follows:1.The PMo/BEN,PMo/Dia,PMo/AC and PMo/SiO2 four kinds of supported polyoxometalats catalysts were prepared by dipping method and Sol-gel process,and the supported catalysts were characterized by FT-IR,XRD and BET.Results show that PMo highly dispersed on the surface of carrier and remained Keggin structure.2.With hydrogen peroxide?H2O2?as oxidant,PMo/Ben,PMo/Dia,PMo/AC and PMo/SiO2were used as catalysts to study the reaction properties of the catalytic iodine ion oxidation into iodine.The repeated performance of the catalysts was investigated,and the effects of the dosage of hydrogen peroxide,catalyst dosage,reaction temperature and ph of solution on the catalytic efficiency of the supported catalysts were studied.The results show of follows:?1?When PMo/BEN as the catalyst,the reaction rate reached 1.65×10-5 mol/?L·s?under the best condition(T=55?,pH<1.8,3.6×10-3 mol·L-1 H2O2 and 8%load capacity),which 1.65×103times more than the reaction without catalyst.In 10 minutes,the conversion rate of iodine ions reached 99%.?2?When PMo/Dia as the catalyst,the reaction rate reached 2.25×10-55 mol/?L·s?under the optimized condition?T=50?,2.0×10-33 mol·L-11 H2O2 pH=1.6 and 7%load capacity?,which2.25×103 times more than the reaction without catalyst.In 10 minutes,the conversion rate of iodine ions reached 99.7%.?3?When PMo/AC as the catalyst,the average reaction rate reached 2.7×10-5mol/?L·s?under the optimized condition?T=50?,1.8 times theoretical value H2O2,1.4g/L PMo/AC,pH=1.8 and40%load capacity?.In 10 minutes,the conversion rate of iodine ions reached 99.7%,the reaction rate increased by 2.7x103 times compared with without catalyst.?4?When PMo/SiO2 as the catalyst,at the end of the reaction,the reaction rate reached3.38×10-5mol/?L·s?under the optimized condition(T=50?,3.5×10-33 mol·L-1H2O2,pH=1.8 and 18%load capacity).The conversion rate of the reaction rate was 3.38×103times higher than without catalyst,and the conversion rate of the catalyzed iodine ions in 10min was as high as 87.2%.3.The supported phosphorus-molybdenum polyoxometalats have good dispersibility,thermal stability and catalytic activity,as catalysts for the oxidation of iodine ions can greatly reduce the dosage of catalyst,shorten the reaction time,the conversion rate of iodine ions is over 95%and the catalyst can be reused many times.The main reasons for the difference of the catalytic activity of the different supported polyoxometalats under the same conditions are the structure of the carrier,the dispersion of the polyoxometalats on the carrier,the acidity and alkalinity of the carrier surface and the adsorption mechanism. |
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