Applied Catalysis A: General 462–463 (2013) 31–38 Contents lists available at SciVerse ScienceDirect Applied Catalysis A: General j ourna l h om epage: www.elsevier.com/locate/apcata Selective epoxidation of olefins over Co(II)-Schiff base immobilised on KIT-6 P. Visuvamithiran, M. Palanichamy, K. Shanthi, V. Murugesan ∗ Department of Chemistry, Anna University, Chennai 600025, India a r t i c l e i n f o Article history: Received 26 February 2013 Received in revised form 3 May 2013 Accepted 6 May 2013 Available online 14 May 2013 Keywords: KIT-6 Co-Schiff base Solvent polarity Epoxidation Olefins H2O2 a b s t r a c t Co-Salen complex immobilised on amine functionalised mesoporous KIT-6 (Co-S-KIT-6) was prepared by post synthetic method. The synthesised materials were characterized by techniques such as small angle XRD, FT-IR, DRSUV–vis, thermal analysis, N 2 sorption, ESR, SEM and TEM. The small angle XRD patterns, N 2 sorption studies and TEM images clearly revealed immoblisation of Co-Salen complex inside the pores of KIT-6. Further, decrease in the surface area, pore volume and pore diameter compared to parent KIT-6 also confirmed the immobilisation of Co-Salen complex inside the mesopores. The catalytic activity of Co-S-KIT-6 was tested in the liquid phase epoxidation of olefins using H 2 O 2 as the oxidant. The influence of reaction parameters such as catalyst amount, reaction temperature, solvent and reaction time on the catalytic activity of Co-S-KIT-6 was also studied. The solvent polarity played a key role in the conversion and selectivity. Polar aprotic solvent such as acetonitrile exhibited high conversion with high selectivity of the product. Further, it was demonstrated that Co-S-KIT-6 can be recycled upto five cycles without loss of its catalytic activity. In addition, the catalyst was found to be highly active, stable and selective. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Epoxides are major reaction intermediates and raw material for the synthesis of many fine chemicals [1,2]. Conventional epoxi- dation reaction employs peracids, perchlorates and other organic peracids, which leave large amount of toxic and hazardous organic waste. The catalytic epoxidation of alkenes using metal complexes and metal-salen complexes in homogeneous condition showed good activity and selectivity [3–15]. Among these, cobalt based complexes have been extensively used for the epoxidation of var- ious alkene substrates with different oxidants [14–18]. However, these homogeneous catalysts are relatively difficult to recover and recycle. Recently, immobilization of homogeneous catalysts on suitable supports have been attempted to demonstrate high active and selective in addition to easy recovery and recycle. The homogeneous transition metal complexes can be anchored onto solid supports such as mesoporous silica, carbon materials, clay and organic polymers [19]. However, majority of supported homogeneous catalysts showed significant loss of activity due to constraints of product diffusion. The supports with high surface area, large pore diameter and high pore volume enhance the mass ∗ Corresponding author. Tel.: +91 44 22357023/22358645; fax: +91 44 2220066/22201213. E-mail address: v murugu@hotmail.com (V. Murugesan). transport property and thereby facilitate good catalytic perfor- mance. Generally, metal complexes are immobilised onto solid sup- ports using methods such as covalent anchoring, encapsulation, coordination and ion interaction. However, covalent anchoring of homogeneous complexes is an effective method. Mesoporous silica materials possess defective Si-OH groups and hence they provide effective anchoring sites for amine spacer [20]. Recently, Karandikar et al. [21] reported Cu/Co Salen immobilised MCM-41 catalysts through amino silane linkers by adduct formation and these heterogeneous catalysts were found to be active for epox- idation reactions using tert-butyl hydroperoxide (TBHP) as the oxidant. There are several reports on the epoxidation of alkenes with TBHP as the oxidant [22,23]. Considering the economic and environmental aspects of hazardous TBHP, H 2 O 2 was used as the oxidising agent in the present study. Since water is the only expected by-product, application of this reagent is undoubtedly appealing provided efficient catalysis is accomplished. However, the epoxidation catalysts should activate H 2 O 2 without radical for- mation. Similarly the choice of solvent is also important for the organic transformations as physical and toxicological properties of solvent have pivotal influence on its use both in the laboratory and industrial scale. KIT-6 has been chosen as the host for immobilisa- tion of cobalt Schiff base complex since it is a well-ordered three dimensional cage type porous structure. It can offer resistant to pore blocking and provide good mass transfer of reactant molecules 0926-860X/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcata.2013.05.007