[2009月01月06日]

 
       我组在层状化合物组装催化剂用于环氧化反应的研究连续取得新进展,继开发了层状双氢氧化物(LDH)选择性组装原位多金属含氧簇(POM)催化剂的新合成方法(刘鹏、李灿等Journal of Catalysis, 256 (2008) 345, DOI: 10.1016/j.jcat.2008.03.022 )后,最近,针对这种新催化剂制备方法的普适性及其环氧化催化性能的深入研究结果又被Journal of Catalysis接受发表(Peng Liu, Changhao Wang and Can Li, 2009, Journal of Catalysis, DOI: 10.1016/j.jcat.2008.12.018)。

       发展简单、稳定和高效的多相环氧化催化剂一直是科学研究的挑战之一。这项工作利用了LDH材料具有高的层间阴离子交换能力和层板正电荷密度,实现了多种原位自组装生成的POM催化剂的选择性固载。将得到的LDH-POM催化剂用于30% H2O2为氧化剂的烯烃环氧化中发现,在不使用有机溶剂的条件下,多相催化剂的环氧化选择性明显高于均相POM催化剂。在多种烯丙基醇的环氧化反应中表现出高达99%的化学选择性,95%的H2O2利用效率和37 000 h-1的TOF;并且多相催化剂能够重复使用多次,表现出较高的催化稳定性。该工作不仅提供了一种简单而高效的多相化催化剂的合成方法,而且为探索高选择性的绿色环氧化途径提供了借鉴,所适用的多相环氧化反应具有良好的应用前景。

 

Epoxidation of allylic alcohols on self-assembled polyoxometalates hosted in layered double hydroxides with aqueous H2O2 as oxidant

Peng Liu, Changhao Wang and Can Li

Journal of Catalysis, 262: 159-168 2009. Full paper DOI: 10.1016/j.jcat.2008.12.018

Abstract

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 H2O2 as 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% H2O2 efficiency and 37200 h-1 TOF 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.

Keywords

Heterogeneous catalysis; Epoxidation; Self-assembled polyoxometalates; Layered double hydroxides; Allylic alcohols; Hydrogen peroxide