Synthesis And Characterization Of Substituted Tungstosilicate/Silica

HPA is one of excellent catalytic agent,it has high activity,high selectivity and non-pollution,The new materials become researched hotspot recently.The Keggin-structured polyoxometalates includingα-SiW₁₁O₃₉M(M=Co,Mn,Cu),have been prepared, and supported by SiO₂,then characterized by IR spectroscopy,X-ray diffraction and UV spectroscopy.The structure of the catalysts, includingα-K₂H₄SiW₁₁CoO₃₉·4H₂O/SiO 2,α-K₂H₄SiW₁₁MnO₃₉·5H₂O/SiO₂,α-K₂H₄SiW₁₁CuO₃₉·6H₂O/SiO₂ ,are determined by TG-DT G.The catalysts were used in the esterification,to examination the catalytic activity.In the intermittent,the molar ratio of acetate to ethanol,the amount of the catalysts,the temperature of reaction and the amount of the carrier are studied,then the best reaction condition is determined.The best condition ofα-K₂H₄SiW₁₁CoO₃₉·4H₂O/SiO₂ are the dip time 24 h,temperature of roasting 200℃,the molar ratio of acetate to ethanol 1:6,the content of catalytic 0.63%,the carrier 3 mL,and the temperature 145～150℃.Then the esterification yield could reach 90.7%.The best condition ofα-K₂H₄SiW₁₁MnO₃₉·5H₂O/SiO₂ are the dip time 24 h,temperature of roasting 200℃,the molar ratio of acetate to ethanol 1:7,the content of catalytic 2.1%,the carrier 9 mL,and the temperature 140℃.Then the yield could reach 86.7%.The best condition ofα-K₂H₄SiW₁₁CuO₃₉·6H₂O/SiO₂ are the dip time 24 h,temperature of roasting 200℃,the molar ratio of acetate to ethanol 1:6,the content of catalytic 1.9%,the carrier 5 mL,and the temperature 130～135℃.Then the yield could reach 85.5%.The recycling and reuse are also examined in this paper,which shows that the catalysts are easily separated from the system,and continued for the next reation.The method is simple,easily operated,high selectivity,side effects less, esterification rate is still high after be reused 5 times,and don't corrode equipment and pollute the environment.