钛取代的钨硅杂多配合物位置异构体的合成、表征及催化性能

Synthesis, Characterization and Catalytic Activity of Positional Isomers of Titanium Substituted Tungstosilicates

合成了通式为α K6[SiW11TiO40 ]·xH2 O、βi K6[SiW11TiO40 ]·xH2 O(βi=β1,β2 ,β3 )的 4种异构体 ,通过元素分析、IR光谱、UV光谱、极谱和183 WNMR光谱进行了表征。183 WNMR光谱数据指出 ,在α、β1、β3 阴离子中有 6种环境的W原子 ,β2 阴离子中有 9种环境的W原子 ,表明所合成的化合物均为单取代的Keggin结构杂多配合物。极谱数据表明 ,杂多阴离子的极谱半波电位E1/ 2 顺序为 β2 >β1>β3 >α ,它们的还原过程包括Ti(Ⅳ )的 1电子还原和W (Ⅵ )的 2电子还原过程。所合成的异构体在催化以H2 O2 为氧化剂的顺丁烯二酸环氧化反应中有较好的催化活性 ,且 β异构体的催化活性高于α异构体。

Four heteropoly isomers α-K 6\[SiW 11TiO 40\]·xH 2O and β i-K 6\[SiW 11TiO 40\]·xH 2O(β i=β 1,β 2,β 3) were synthesized and characterized by elemental analysis, IR, UV spectrometry, polarography, cyclic voltammetry and 183W NMR. The 183W NMR results suggested that tungsten atoms are in six chemical enviroments for α,β 1,β 3 -isomers and in nine chemical enviroments for β 2-isomer, indicating compounds formed are all mono-substituted heteropoly complexes of Keggin structure. The order of polarographic half-wave potential E 1/2 of the heteropoly anions was as follows:β 2>β 1>β 3>α. Their reduction processes involved an one-electron reduction of Ti(Ⅳ) and a pair of two-electron reduction of W(Ⅵ). The synthesized isomers showed better catalytic activity in epoxidation of maleic acid with H 2O 2 and the β-isomer was higher than α-isomer in catalytic activity .