Epoxidation of allylic alcohols on self-assembled polyoxometalates hosted in layered double hydroxides with aqueous H2O2 as oxidant
Epoxidation of allylic alcohols on self-assembled polyoxometalates hosted in layered double hydroxides with aqueous H2O2 as oxidant
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DOI：
10.1016/j.jcat.2008.12.018
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发表时间：
2009-02
影响因子：
7.3
通讯作者：
Peng Liu;Changhao Wang;Can Li
中科院分区：
文献类型：
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作者：
Peng Liu;Changhao Wang;Can Li
采用选择性离子交换法将一系列自组装多氧杂环丁烷酸盐（POM）催化剂直接固定在层状双氢氧化物（LDH）上。三明治型POM比Keggin型POM更适合于直接固定LDH，因为它不需要严格的pH控制，而且LDH宿主可以保持完整。在不使用有机溶剂的条件下，以H2 O2水溶液为氧化剂，考察了LDH-POM催化剂在烯丙醇环氧化反应中的催化活性。非均相LDH-POM催化剂显示出比相应的均相Na-POM催化剂高得多的环氧化物选择性，这可以归因于碱性LDH主体对酸催化的环氧化物水解的抑制的有益效果。POM客体和LDH主体之间的协同作用可以实现高达99%的环氧化物选择性，95%的H2 O2效率和37200 h-1 TOF，而无需碱添加剂和pH控制，并且主-客体催化剂可以容易地回收而没有明显的催化性能损失。
A series of self-assembled polyoxometalate (POM) catalysts were directly immobilized into layered double hydroxides (LDH) by a selective ion-exchange method. Sandwich-type POM species are found to be more favorable than Keggin-type POM for the direct immobilization in LDH, because strict pH controlling is not needed and the LDH hosts can be kept intact. The resulting LDH–POM catalysts were evaluated in the epoxidation of allylic alcohols with aqueous H2O2as the oxidant without using organic solvent. The heterogeneous LDH–POM catalysts show much higher epoxide selectivity than the corresponding homogeneous Na–POM catalysts, which can be attributed to the beneficial effect of basic LDH host on the suppression of the acid-catalyzed epoxide hydrolysis. The cooperation between the POM guest and the LDH host can achieve up to 99% selectivity of epoxide, 95% H2O2efficiency and 37200 h−1TOF without the need of base additives and pH controlling, and the host-guest catalysts can be readily recycled with no apparent loss of catalytic performance.