{P8W48}-轮型多金属氧酸盐的合成及氧化催化性能

六缺位Dawson型钨磷酸盐K12H2P2W12O48·24H2O在NaAc-HAc缓冲溶液中发生自聚,形成了Na21Na12H7P8W48O184]·70H2O(简写为Na-P8W48)轮型化合物.利用单晶X射线衍射、IR和XRD对Na-P8W48进行了表征,在该化合物的轮内12个活性位均被Na+占据.以环己醇氧化合成环己酮为模型反应,探讨了{P8W48}的氧化催化性能.考察了不同物料比、催化剂用量、反应时间、温度及催化剂的溶解性对反应的影响.结果表明,当环己醇/H2O2的摩尔比为1∶2.2,环己醇/{P8W48}(以W计)的摩尔比为200∶1,80℃反应3h,环己酮产率最高,在均相体系时产率可达93%,是环己醇氧化合成环己酮的优良催化剂.

Synthesis and oxidation catalytic activity of wheel-type { P8W48 } polyoxometalates

A Wheel-type tungstophosphate Na21Na12H7P8W48O184]·70H2O, with twelve active sites occupied by Na＋, was synthesized in NaAc-HAc buffer solution by self-assembly of the hexavacant Dawson-type tungstophosphate K12H2P2W12O48·24H2O. It was characterized by single crystal Xray diffraction, IR and XRD analysis. Using the oxidation of cyclohexanol to cyclohexanone as a model reaction, the catalytic activity of {P8 W48 } was evaluated,and the reaction conditions, such as the molar ratio of starting materials, the amount of catalyst, the reaction time, the reaction temperature, and the solubility of catalyst, were systemically explored. The results show that the optimum conditions for the oxidation of cyclohexanol were： the molar ratio of cyclohexanol/H2o2 was 1 ： 2.2, the molar ratio of cyclohexanol/{ P8 W48 } （based on W） was 200： 1 ,and the reaction time was 3 h. Furthermore,the yield of the cyclohexanone can reached 93% using {PsW48 } as a homogenous catalyst, the wheel-type POMs were excellent catalysts for the oxidation of cyclohexanol to cyclohexanone.