Local environment of isolated iron in mesoporous silicate catalyst FeTUD-1 Natas ˇa Novak Tus ˇar a, * , Alenka Ristic ´ a , Sas ˇa Cecowski a , Iztok Arc ˇon b,c , Ka ´roly La ´za ´r d , Heinz Amenitsch e , Venc ˇeslav Kauc ˇic ˇ a,f a National Institute of Chemistry, Hajdrihova 19, 1000 Ljubljana, Slovenia b University of Nova Gorica, Vipavska 13, 5000 Nova Gorica, Slovenia c Institute Joz ˇef Stefan, Jamova 39, 1000 Ljubljana, Slovenia d Institute of Isotopes, HAS, P.O. Box 77, 1525 Budapest, Hungary e ELETTRA Synchrotron Light Laboratory and Laboratorio Nazionale TASC-INFM, Area Science Park S.S.14, Km. 163.5 I-34012 Basovizza-Trieste, Italy f Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, 1000 Ljubljana, Slovenia Received 15 October 2006; received in revised form 1 March 2007; accepted 2 March 2007 Available online 12 March 2007 Abstract Mesoporous silicate catalyst FeTUD-1 containing only isolated iron was synthesized. Local environment of iron was investigated by X-ray Absorption and Mo ¨ ssbauer spectroscopies. XANES (X-ray Absorption Near Edge Structure) studies show that iron in the as-syn- thesized and template-free FeTUD-1 is present in the form of Fe 3+ ions in coordination geometries posses an inversion center. EXAFS (X-ray Absorption Fine Structure) analyses reveal that iron cations in the as-synthesized sample are coordinated to four oxygens at the distance of 1.87 A ˚ and in the template-free sample to one oxygen at 1.86 A ˚ and five oxygens at 2.0 A ˚ distances. Mo ¨ ssbauer spectroscopy proves the presence of iron in Fe 3+ form in template-free sample. Moreover, it determines Fe 3+ in two types of distorted octahedral coordinations. Ó 2007 Elsevier Inc. All rights reserved. Keywords: FeTUD-1; Isolated iron; SAXS; XANES; EXAFS; Mo ¨ ssbauer 1. Introduction Porous transition-metal modified silicates are of funda- mental importance in catalysis [1]. A new templating method using small, inexpensive non-surfactant triethanol- amine was reported for the preparation of mesoporous sil- icate with 3D sponge-like pore structure denoted as TUD-1 [2] and mesoporous alumina with the same structure [3,4]. This novel templating method provided also an oppor- tunity to design transition-metal modified mesoporous silicate catalysts. Titanium-modified Ti-TUD-1 catalyst is about six times more active for cyclohexene epoxidation with tert-butylhydroperoxide (TBHP) than framework- substituted Ti-MCM-41 and has similar activity to Ti- grafted MCM-41 [5,6]. Cobalt-modified Co-TUD-1 [7–9] and chromium-modified Cr-TUD-1 [9] catalysts were also shown to be active in cyclohexene oxidation with TBHP. Recently, Cr-TUD-1 catalyst was reported to be a new vis- ible light-sensitive photo-catalyst for selective oxidation of propane [10] and Al-TUD-1 was shown to be a versatile catalyst for the alkylation of phenol [11]. Iron-modified FeTUD-1 was synthesized and tested in cyclohexane oxidation [8,9],N 2 O decomposition [8] and Friedel-Crafts benzylation of benzene [12]. Characteriza- tion results of iron local environment in FeTUD-1 prove that different active sites can be generated, ranging from 1387-1811/$ - see front matter Ó 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2007.03.002 * Corresponding author. Tel.: +38614760410; fax: +38614760300. E-mail address: natasa.novak@ki.si (N.N. Tus ˇar). www.elsevier.com/locate/micromeso Microporous and Mesoporous Materials 104 (2007) 289–295