Vanadium-containing K10 was synthesized and characterized by electron paramagnetic resonance, nuclear magnetic resonance, N-2 adsorption at 77 K and chemical analysis. Two different vanadium species have been identified in dried V-K10, the first is V4+ in square pyramidal or distorted octahedral environment and the second is V5+ in a tetrahedral environment that is present in an isolated monomeric state (VO43-) and dimeric state [O3V-O-VO3](4-). When V-K10 was calcined in air, V4+ was oxidized to V5+ with a change in the coordination from square pyramidal or distorted octahedral to tetrahedral. Vanadium species, in the highest oxidation state (V), were found to be the catalytic sites that readily interact with tert-butylhydroperoxide (TBHP) to offer an active and selective catalytic system for the oxidation of sulfides. This catalytic system was studied in the asymmetric oxidation of methyl pheryl sulfide, using two types of chiral modifier, and gives excellent conversions and suffoxide selectivity, together with an enantioselectivity in the range of 9-11 % ee. (c) 2006 Elsevier B.V. All rights reserved.