Oxidation properties of niobium and tin in mesoporous matrices were investigated in oxidation of cyclic ketones, cyclic olefins and cyclic keto-olefins with hydrogen peroxide as an oxidation agent. Mesoporous molecular sieves of MCM-41 and MCM-48 types were synthesized and niobium and tin were incorporated into the structure. X-ray diffraction and nitrogen sorption isotherms confirmed a high-quality of these mesoporous molecular sieves even after incorporation of Nb and/or Sn. It was shown that niobium selectively oxidizes double bond of the substrates to epoxide followed by further hydration and forms diols, and keto-diols in the second step of the reaction. On the other hand, tin carries out Baeyer-Villiger oxidation of cyclic ketones to lactones without further consecutive reactions while Nb is inactive in this reaction. When substrate contains both C=C double bond and carbonyl group on the same ring, Nb oxidizes preferentially the double bond with a much higher activity than Sn. (c) 2007 Elsevier B.V. All rights reserved.