Tungsten-incorporated cage-type mesoporous silicate: W-KIT-5 Anand Ramanathan a , Rajamanickam Maheswari a,c , Brian P. Grady d , David S. Moore e , Dewey H. Barich f , Bala Subramaniam a,b,⇑ a Center for Environmentally Beneficial Catalysis, The University of Kansas, Lawrence, KS 66047, USA b Department of Chemical and Petroleum Engineering, The University of Kansas, Lawrence, KS 66045, USA c Department of Chemistry, Anna University, Chennai 600025, India d School of Chemical, Biological and Materials Engineering, University of Oklahoma, Norman, OK 73019, USA e Microscopy and Imaging Laboratory, University of Kansas, Lawrence, KS 66045, USA f Solid State NMR Facility, McCollum Laboratory, University of Kansas, Lawrence, KS 66047, USA article info Article history: Received 8 December 2012 Received in revised form 2 February 2013 Accepted 8 March 2013 Available online 26 March 2013 Keywords: KIT-5 Tungsten Mesoporous Acidity abstract Tungsten-incorporated cage-like cubic three-dimensional mesoporous silicate, KIT-5, was successfully synthesized by one-step direct hydrothermal synthesis procedure employing Pluronic F127 triblock copolymer as the structure directing agent under acidic conditions. The resulting material, labeled as W-KIT-5, was characterized by XRD (SAXS and WAXS), N 2 sorption, HR-TEM, DR-UV–Vis, 29 Si MAS NMR, Raman spectroscopy, H 2 -TPR and NH 3 -TPD to better understand the morphology, textural proper- ties and nature of tungsten coordination. With an increase in tungsten content, the surface area decreased from 964 (for Si/W = 100) to 425 m 2 /g (Si/W = 10) and the corresponding total pore volumes decreased from 0.68 to 0.42 cm 3 /g. Interestingly, narrow pore size distributions centered around approx- imately 9.1 nm were observed for all W-KIT-5 samples. Depending on the loading, the incorporated tung- sten is shown to exist in the KIT-5 framework as well as in the extraframework position by complementary analytical techniques. The W-KIT-5 samples are also shown to possess low to medium type acid strength. Ó 2013 Elsevier Inc. All rights reserved. 1. Introduction Tungsten has been supported as catalytically active species on different support materials and investigated as catalyst for olefin metathesis [1–8], acid catalyzed reactions such as isomerization [9–17] and dehydration [18–26], and the selective oxidation of al- kenes [27–31]. Among various supports, ordered mesoporous sili- cates are promising due to their tunable pore structure, high surface area and pore volume. For instance, tungsten was incorpo- rated into MCM-41 silicate in an acidic synthesis medium as iso- lated W sites that were shown to be active for hydroxylation of cyclohexene with H 2 O 2 [32].Tungsten was also incorporated into the framework of MCM-41 under basic conditions by Klepel et al. [33]; however, significant W loss was observed during the washing of as-synthesized samples. Tungsten-containing mesoporous MCM-48 was prepared in an acidic medium [34] and also by a ra- pid room temperature synthesis procedure under basic conditions [35]. Both these synthetic procedures showed significantly lower tungsten amounts in the final solid materials compared to the tungsten content in the synthesis gel. In a one-step co-condensa- tion sol–gel method, tungsten was incorporated into SBA-15 under acidic conditions [7,36]. It should be noted that in all the tungsten- containing porous materials noted above, the framework tungsten species are proposed to be active sites for the reactions. On the other hand, zirconia-supported tungsten oxide (WO 3 /ZrO 2 ) materi- als has been studied as strong solid acid catalysts [18] and the gen- eration of acid sites is attributed to a certain type of cluster consisting of multiple W, Zr, O, and H atoms [37]. Typically, in W containing porous silicates, the Lewis acid sites are generated from coordinatively unsaturated W 6+ species [38]. In W-doped SBA-15, the presence of both W 6+ and W 5+ species were attributed to the generation of Lewis and Brønsted acid sites [36]. Interestingly, nanoparticles of WO 3 supported on MCM-48 [29] and SBA-15 [31] silicates are shown to be active sites for the oxidation of olefins. Ordered mesoporous materials such as MCM-41 and SBA-15 possess a hexagonal pore structure having a one-dimensional array of pores. In contrast, three-dimensional mesoporous silicates such as SBA-1, SBA-16, and KIT-5 have interconnected cage-type pores in which bulky reaction intermediates can be accommodated. Among cage type mesoporous silicates, KIT-5 is interesting due to its highly ordered, cubic (Fm3m), closely-packed symmetry with tunable cage-type pores that result from its hydrothermal 1387-1811/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.micromeso.2013.03.019 ⇑ Corresponding author at: Center for Environmentally Beneficial Catalysis, The University of Kansas, Lawrence, KS 66047, USA. Tel.: +1 785 864 2903; fax: +1 785 864 6051. E-mail address: bsubramaniam@ku.edu (B. Subramaniam). Microporous and Mesoporous Materials 175 (2013) 43–49 Contents lists available at SciVerse ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso