Physicochemical Properties of Vanadium-Containing Montmorillonite in Epoxidation of Allylic Alcohol

Abstract

Vanadium-containing aluminosilicate molecule sieves were observed to exhibit remarkable catalytic activity in oxidation of hydrocarbons, notably epoxidation of allylic alcohol. In this paper, we review the spectroscopic characterisation of framework incorporation and redox behavior of vanadium in both natural montmorillonite and K10. NMR and EPR studies of coordination and oxidation state of vanadium in dried and calcined samples show that vanadium exists mainly in a tetrahedral oxygen coordination as an isolated monomeric state (VO43-) in V-mont and also as dimeric state [O3V-O-VO3]2- in V-K10 case. The vanadium, in both systems, shows redox properties, changing its oxidation state readily between V4+ and V5+. The development of a high surface area in the V-K10 case, provides a well-dispersed vanadium species, which inceases the initial rate compared to the V-mont one. This vanadium species, in highest oxidation state (V), is found to be the catalytic centre in epoxidation of allylic alcohols, according to a heterolytic mechanism via a tert-butylhydroperoxide-vanadium intermediate.