Applied Catalysis A: General 408 (2011) 105–116 Contents lists available at SciVerse ScienceDirect Applied Catalysis A: General j ourna l ho me page: www.elsevier.com/locate/apcata Performance evaluation of mesoporous host materials in olefin epoxidation using Mo(II) and Mo(VI) active species—Inorganic vs. hybrid matrix Nuno U. Silva a , Cristina I. Fernandes a , Teresa G. Nunes b , Marta S. Saraiva a , Carla D. Nunes a,∗,1 , Pedro D. Vaz a,∗ a CQB, Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal b CQE, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal a r t i c l e i n f o Article history: Received 26 May 2011 Received in revised form 6 September 2011 Accepted 11 September 2011 Available online 16 September 2011 Keywords: Epoxidation MCM-41 Molybdenum Periodic mesoporous organosilicas Single-site catalyst a b s t r a c t The [Mo VI O 2 Cl 2 (thf) 2 ] and [Mo II I 2 (CO) 3 (MeCN) 2 ] precursor complexes, were immobilized in a hybrid periodic mesoporous organosilicas (PMO)-type material. These new hybrid matrix materials were pre- pared in one pot synthesis, containing the bidentate N,N ′ -ligand (glypy) in the material. In a second approach, the ordered mesoporous silica MCM-glypy was prepared using a tethered approach by a step- wise procedure. The metal complexes were grafted in both types of materials to obtain heterogeneous pre-catalysts. The modified materials have been characterized by powder X-ray diffraction, N 2 adsorption, and solid-state CP MAS NMR ( 13 C, 29 Si). All metal containing materials were tested as catalysts in epoxidation of 1-octene, cyclooctene and styrene with tert-butylhydroperoxide (TBHP) at 328 K. Selectivity to octene and cyclooctene epoxides was complete. The new PMO materials described in this work are outstanding catalysts for any of the transformations described. In fact, cyclooctene selectivity based on TBHP consumption is found to be almost independent of the mol ratio attesting the efficiency of the catalysts. They are also effective under stoichiometric olefin/oxidant ratio. In addition, a mechanism for acid catalyzed benzaldehyde formation is proposed as well as the conversion of Mo(II) to Mo(VI) under catalysis. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The quest for efficient heterogeneous catalysts strongly depends on the capability to assemble an active and selective homogeneous catalyst for a given reaction and an appropriate support that will prevent catalyst loss and facilitate its recovery, keeping the activ- ity. Products can be also easily obtained, a fact that contributes to the preference for heterogeneous processes in chemical industry [1,2]. Environmental issues are also relevant, namely the search for product selectivity or the use of solventless conditions [3,4]. Among possible supports, the family of MCM materials, in particular MCM-41, developed by Mobil in 1992, offers a wide range of advantages, from the ordered structure of hexagonal channels with diameters between 2 and 50 nm and high surface area, to the mechanical stability, and the chemical nature of its walls with reactive SiOH groups [5,6]. These groups may react with molecules containing SiOR functionalities, which will bind ∗ Corresponding author. Tel.: +351 217 500 877; fax: +351 217 500 088. E-mail addresses: cmnunes@fc.ul.pt (C.D. Nunes), pmvaz@fc.ul.pt (P.D. Vaz). 1 Tel.: +351 217 500 876; fax: +351 217 500 088. to the MCM’s silanol surface through covalent bonds [7]. These may include direct grafting of either metal complexes or ligands. The latter are also able to bind to metal complexes leading to a more elaborated preparation of the resulting materials. This pro- cedure, known as tethering [8,9], is usually more efficient, since the active metal complex to lie inside the host material is pre- pared by steps, leading to a better control of metal loadings [8]. Application of MCM materials extend to several fields besides catal- ysis, such as photo or electro-chemistry studies [10–13]. More recently, the introduction of organic molecules within the inor- ganic framework has been made possible by a one-step synthetic procedure leading to hybrid organic–inorganic materials known as periodic mesoporous organosilicas (PMO) [7,14–23]. Silylated pre- cursors containing phenyl rings, thiophene, imidazole, ferrocene molecules, and many other organic groups have been used to form the walls in such a way as to maintain the mesoporous structure [23–33]. Whereas in principle these two synthetic routes should yield the same material, the formation of an ordered structure is highly dependent on the nature and amount of the organic group of the precursor [21,22]. In this work, we report the use of an asymmetric ligand, biden- tate N,N ′ -ligand (glypy), which can react unambiguously with the 0926-860X/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2011.09.012