银含量对二氧化硅固载磷钨酸银催化四氢呋喃聚合反应性能的影响

通过共浸渍法合成了一系列担载型杂多酸银盐催化剂Ag_xH_3-xPW/SiO₂ (x=0.5, 1.0, 1.5, 2.0, 2.5, 3.0),由于催化剂在极性溶剂中的不溶性, 在合成聚四氢呋喃的反应中显示了高反应活性和稳定性能. Ag离子取代含量和银盐的担载量对催化剂活性会产生显著影响. Ag 离子含量的不同会导致磷钨酸银盐的晶相结构和催化剂的酸性质发生变化. x=2.0 时, 催化剂Ag₂HPW/SiO₂达到最大酸强度和最高催化聚合反应活性. 当银盐Ag₂HPW的担载量为30% (质量分数)时, 催化剂能达到高分散度和高的四氢呋喃聚合反应活性. 与普通二氧化硅担载的磷钨酸催化剂HPW/SiO₂对比, 担载型磷钨酸银盐30%Ag₂HPW/SiO₂拥有优异的重复使用性能, 循环4 次后催化活性只有轻微下降. 通过引入Ag离子合成的新型担载磷钨酸银盐30%Ag₂HPW/SiO₂, 反应稳定性能明显改进, 得到拥有稳定平均分子量的产物聚四氢呋喃.

Effect of Silver Content on Catalytic Performances of SiO2-Supported Silver Tungstophoric Acid for the Synthesis of Polytetrahydrofuran

A series of supported silver salts of heteropolyacid Ag_xH_3-xPW/SiO₂ (x=0.5, 1.0, 1.5, 2.0, 2.5, 3.0) were synthesized and showed high reactivity and stability in tetrahydrofuran polymerization, which were due to the salts'' insolubility in polar solvent. The amount of Ag ion replaced in the salt and the amount of the salt loaded on the silica significantly influenced the catalytic performance. Change in the Ag content of the supported silver salt altered the crystal phase composition of the silver tungstophoric acid and catalyst''s acid strength. The Ag_xH_3-xPW/SiO₂ catalyst had the highest acid strength and the highest polymerization activity when x=2.0. When the Ag₂HPW loading was 30% (mass fraction), the catalyst exhibited the best dispersion and highest activity for the polymerization of tetrahydrofuran. Compared with the conventional silica supported heteropolyacid (HPW/SiO₂) catalyst, the present 30%Ag₂HPW/SiO₂ displayed excellent reusability, with its reactivity only slightly declining after 4 reuses. Through the introduction of the Ag ion, the stability of the novel supported 30%Ag₂HPW/SiO₂ was significantly improved and the obtained polymer product, polytetrahydrofuran, had a stable average molecular weight.