A new route for the synthesis of manganese incorporated SBA-15 G. Satish Kumar a , M. Palanichamy a , M. Hartmann b , V. Murugesan a, * a Department of Chemistry, Anna University, Chennai, Tamil Nadu 600 025, India b Advanced Materials Science, Institute of Physics, University of Augsburg, Augsburg 86159, Germany Received 26 May 2006; received in revised form 29 August 2007; accepted 4 September 2007 Available online 18 September 2007 Abstract Manganese incorporated SBA-15 was synthesized by pre-hydrolyzing tetraethyl orthosilicate and manganese acetate above the iso- electric point of silica (pH 2–4) employing triblock copolymer as the template. The synthesized material was characterized by AAS, XRD, N 2 adsorption, FT-IR, TGA, ESR, diffuse reflectance UV–Vis and SEM techniques. The XRD results showed well-ordered hex- agonal array of the synthesized materials. The thermal stability of synthesized material was evaluated using TGA. The results of AAS, ESR and UV–Vis DRS revealed that almost all manganese added in the initial reaction is introduced into the product at higher pH. Thus, higher pH of the synthesis gel favoured better incorporation of manganese in the framework. The incorporation of Mn 2+ in the product was confirmed by ESR studies, and the presence of Mn 3+ ions was clearly evident from UV–Vis DRS studies. Thus man- ganese exists both as bivalent and trivalent states in all the synthesized materials. Ó 2007 Elsevier Inc. All rights reserved. Keywords: MnSBA-15; Prehydrolyse; ESR; UV–Vis DRS; pH 1. Introduction The researchers at Mobil Corporation reported a series of ordered mesoporous silicates that are designated as M41S, which were synthesized by self-assembly of surfac- tants and inorganic species [1]. The most extensively stud- ied member of the ordered mesoporous material is MCM-41, which possesses large specific surface area, hex- agonal array and uniform mesoporous channels. Many ele- ments such as B, Al, Ga, Mn, V, Nb, Cr, Sn, Zr and Ti have been incorporated into the siliceous framework of MCM related materials to create catalytically active sites [2–5]. However, these materials lack thermal and hydro- thermal stability due to their thin walls. Many efforts have been made to improve the thermal and hydrothermal sta- bility of MCM-41. Highly ordered large pore mesoporous silica molecular sieves SBA-15 with considerably thicker pore walls as compared to MCM-41 have been synthesised using an amphiphilic triblock copolymer as the structure directing agent in highly acidic media [6,7]. SBA-15 exhib- its improved hydrothermal stability as compared to MCM- 41[1,8]. Hence SBA-15 has attracted much attention because of its tunable pore diameter, thicker walls, high hydrothermal stability and potential applications in a wide variety of field. Many interesting works have been reported on the pore structure of SBA-15 [9] and the use of SBA-15 as a template in the preparation of various mesostructured materials [10]. However, pure siliceous SBA-15 limits its practical application especially in catalysis, owing to lack of active sites in the wall. It is difficult to prepare hetero- atom incorporated SBA-15 in strongly acidic synthesis con- dition because under such condition the metals will exist only in the cationic form rather than their corresponding oxo species. Therefore, heteroatom cannot be introduced into the mesoporous walls of silica species by condensation process. Hence, it is of great importance to incorporate het- eroatom on the walls of these mesoporous silica materials prepared under strongly acidic condition. Direct synthesis 1387-1811/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2007.09.012 * Corresponding author. Tel.: +91 44 22203144; fax: +91 44 22200660. E-mail address: v_murugu@hotmail.com (V. Murugesan). www.elsevier.com/locate/micromeso Available online at www.sciencedirect.com Microporous and Mesoporous Materials 112 (2008) 53–60