Epoxidation of alkenes catalyzed by heteropolyoxometalate as pillars in layered double hydroxides

Abstract

The epoxidation of alkenes with hydrogen peroxide or molecular oxygen, in the presence of aldehyde catalyzed by heteropolyoxometalate (HPOM) salts and layered double hydroxides (LDHs) containing HPOM anions as pillars, has been investigated. In the case of oxidation with hydrogen peroxide, a lacunary Keggin-ion, SiW 11O 39 8−, was more active than SiW 12O 40 4−. For this reaction system using hydrogen peroxide, intercalated SiW 11O 39 8− showed higher stability in structure and activity than free K 8SiW 11O 39. For the oxidation using molecular oxygen and aldehyde, SiW 12O 40 4− showed higher activity than SiW 11O 39 8−. It was confirmed that SiW 12O 40 4− was intercalated between the brucite-type layers of the LDHs without change in structure. Ni-containing LDHs without any interstitial polyoxometalate showed high activity for the oxidation of cyclohexene with the combination of O 2 and aldehyde.