Journal of Catalysis 221 (2004) 319–324 www.elsevier.com/locate/jcat Sol–gel synthesis of oxodiperoxo molybdenum-modified organic–inorganic materials for the catalytic epoxidation of cyclooctene Mingjun Jia, Andreas Seifert, and Werner R. Thiel ∗ Institut für Chemie, Technische Universität Chemnitz, Strasse der Nationen 62, D-09111, Chemnitz, Germany Received 28 May 2003; revised 23 July 2003; accepted 29 July 2003 Abstract Hybrid organic–inorganic materials were synthesized by sol–gel copolymerization of the N,N -chelate ligand (3-triethoxysilylpropyl) [3-(2-pyridyl)-1-pyrazolyl]acetamide (1) and tetraethoxysilane (TEOS). Active solid oxidation catalysts can be obtained by introducing oxodiperoxo molybdenum species MoO(O 2 ) 2 into the hybrid sol–gel materials with a ligand-exchange reaction. The molybdenum-containing catalyst, prepared from a sol–gel precursor with relatively large pore volume and high specific surface area, showed a very high stability against leaching of the active species into the liquid phase during the epoxidation of cyclooctene with tert-butyl hydroperoxide ( t BuOOH).  2003 Elsevier Inc. All rights reserved. Keywords: Epoxidation; Hybrid materials; Molybdenum; Peroxides; Sol–gel synthesis 1. Introduction The heterogenization of homogeneous catalysts for li- quid-phase olefin epoxidation is an attractive and important research subject. Extensive effort has been focused on the incorporation of metal-based catalysts onto or into inert supports by different methods, such as substituting active metal sites into molecular sieves or amorphous silica, or encapsulating and grafting organometallic complexes into nano- and mesoporous materials [1–3]. An alternative and highly effective method for the preparation of heterogeneous catalysts is to copolymerize an organic functionalized com- pound, usually bearing an organoalkoxysilane group, and an alkoxysilane by a sol–gel procedure [4–7]. The relatively mild reaction condition of the sol–gel process allows incor- poration of various organic moieties in different inorganic materials and tuneing the material properties in a wide range. Additionally, it is possible to produce hybrid materials with high loading of organic functional groups in combination with a uniform coverage of the resulting surfaces by this technique [5]. Recently, we reported the synthesis of a hybrid hetero- geneous catalyst system by covalent grafting of oxodiper- oxo molybdenum complexes of the type [(L-L)MoO(O 2 ) 2 ] * Corresponding author. E-mail address: werner.thiel@chemie.tu-chemnitz.de (W.R. Thiel). (L-L = (3-triethoxysilylpropyl)[3-(2-pyridyl)-1-pyrazolyl] acetamide (1)) into the mesoporous MCM-41 material [8,9]. The grafted materials are highly active and stable cata- lysts for the liquid-phase epoxidation of cyclooctene with t BuOOH as the oxygen source. The high stability against leaching of active species to liquid phase can be mainly at- tributed to the strong binding between the MoO(O 2 ) 2 unit and the chelate ligand [10–13], and to the formation of cova- lent bonds (Si–O–Si) between the organic ligand system and the inorganic mesoporous material [8]. However, a draw- back of the grafting procedure is that the loading of organic functionalities is often low, mainly limited by the distribu- tion of reactive Si–OH groups and the diffusion limitations of the mesoporous channel. Besides, it is believed that or- ganic groups in a grafted mesoporous material are mainly located on the external surfaces and those parts of the inter- nal surface, which are close to the pore windows, leading to a nonuniform distribution of the organic sites [14]. In this work, we present an alternative for the prepara- tion of a hybrid material with a high loading of oxodiperoxo molybdenum complexes in the matrix of the silicate. The precursors were synthesized by copolymerizing the chelate ligand 1 with TEOS under traditional uncatalyzed and cata- lyzed sol–gel conditions. The desired molybdenum-based catalysts are thus obtained by introducing the oxodiper- oxo molybdenum units into the sol–gel precursor by a ligand-exchange reaction. The catalytic performance of the 0021-9517/$ – see front matter  2003 Elsevier Inc. All rights reserved. doi:10.1016/j.jcat.2003.07.009