[2009.01.06]

 
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