Synthesis of microporous surfactant-templated aluminosilicates David P. Serrano,* a José Aguado, a José M. Escola a and Eduardo Garagorri b a Department of Experimental Sciences and Engineering, ESCET, Rey Juan Carlos University, c/Tulipán s/n 28933, Móstoles, Madrid, Spain. E-mail: dserrano@escet.urjc.es b Department of Chemical Engineering, Complutense University, Av. Complutense s/n, 28040 Madrid, Spain. Received (in Cambridge, UK) 31st July 2000, Accepted 7th September 2000 First published as an Advance Article on the web 2nd October 2000 Microporous aluminosilicates have been synthesized in the presence of organic surfactants according to a procedure based on a two-step sol–gel process at room temperature; varying the surfactant chain length and/or the Si/Al ratio, materials with pore diameters adjustable in the range 1.0–2.5 nm have been obtained; the Al atoms in the as-synthesized samples present tetrahedral coordination, even for materials with high Al content (Si/Al = 6). The M41S family of surfactant-templated mesoporous silicates and aluminosilicates was discovered and characterized in 1992 by Mobil Oil researchers. 1 The presence of Al atoms incorpo- rated into the walls and large pores provide these materials with interesting properties for the catalytic conversion of bulky molecules. 2–4 In past years, a number of studies have been published aimed to the synthesis of mesoporous materials with increasing pore size by incorporation of swelling agents to the synthesis medium or by using block copolymer surfactants. 5–8 Accordingly, micelle-templated silicates and aluminosilicates have been prepared with uniform pore sizes in the range 2–10 nm. 9–13 However, less attention has been devoted to the synthesis of surfactant-templated materials with pore diameters below 2.0 nm. This is an interesting goal as it would contribute to fill the pore size gap existing between microporous zeolitic materials (D p < 1 nm) and surfactant-templated mesoporous solids (D p > 2 nm). Moreover, materials with uniform pore size in the range 1.0–2.0 nm are expected to exhibit interesting shape-selectivity properties in the conversion of large sub- strates. Several papers have recently appeared with the aim of obtaining surfactant templated materials with small pore diameters. Thus, a novel method for tailoring the pore opening size of MCM-41 materials has been reported, 14 although based on a complex post-synthesis treatment with three steps. A completely different approach has been developed by Bagshaw and Haymann, 15 which has led to silicates with pore sizes in the range 1.4–2.0 nm through the use of a new family of w- hydroxy-bolaform surfactants. However, at present it is not clear whether this last alternative would also allow microporous aluminosilicates to be synthesized. In a recent work, 16 we have reported a new method for the preparation of Al-containing micelle-templated silica (Al-MTS) based on a sol–gel process at room temperature. We have found that when increasing the aluminium content, materials with pore sizes in the range 1.5–2.0 nm are obtained. In the present work we show that this method is also useful for the synthesis of Al- MTS solids with pore sizes that can be tailored in the range 1.0–2.0 nm through the variation of both surfactant alkyl chain length and Al content. The materials were synthesized at room temperature accord- ing to the following procedure. The silica and aluminium sources (tetraethyl orthosilicate, TEOS, and aluminium iso- propoxide, IPA) were first hydrolyzed under acidic conditions (aqueous HCl), the starting Si/Al ratio being varied within the range 5–30. The surfactant was added and the mixture obtained was stirred and kept under acidic conditions for 1 h (TEOS/Surf. molar ratio = 0.3). Both cetyltrimethylammonium chloride (CTMACl) and dodecyltrimethylammonium bromide (DTMABr) were employed as surfactants. In a second step, condensation reactions were promoted by dropwise addition of 2 wt% aqueous NH 3 until the gel point is reached. The solid material so obtained was filtered off, washed with deionized water and dried at 110 °C overnight. Finally, it was calcined in N 2 flow at a heating rate of 1 °C min 21 up to 550 °C and then kept in air flow at this temperature for 5 h. Table 1 summarizes the physicochemical properties of different Al-MTS materials prepared. Although in general the samples obtained show Al contents lower than those of the synthesis mixture, a close correspondence is observed among them, even for the synthesis with the lowest Si/Al ratios. TG analysis of the as-synthesized samples show the presence of the surfactant molecules occluded in the pores with weight losses in the range 40–55 wt%, confirming that they can be regarded as micelle-templated materials. Fig. 1 illustrates the XRD spectra of samples prepared with surfactants of different chain length, a sharp diffraction peak at low angle being observed, which is Table 1 Synthesis conditions and physicochemical properties of the synthesized materials N 2 adsorption isotherm (77 K) Surfactant Si/Al (medium) Si/Al (product) Pore volume a / cm 3 g 21 BET surface area b /m 2 g 21 Surfactant content c (wt%) CTMACl 30 45.2 0.93 1180 55 CTMACl 20 31.5 0.66 1020 52 CTMACl 10 18.9 0.56 910 50 CTMACl 5 8.3 0.45 790 43 DTMABr 20 42.4 0.47 960 46 DTMABr 15 18.9 0.40 840 42 DTMABr 8 10.4 0.39 820 35 DTMABr 5 6.3 0.32 770 40 a Measured at p/p o = 0.9. b Measured within the range p/p o = 0.01–0.125. c Determined from the TGA weight loss in the range 150–450 °C. Fig. 1 XRD spectra of calcined samples: (a) DTMABr, Si/Al = 6.3 and (b) CTMACl, Si/Al = 45.2. This journal is © The Royal Society of Chemistry 2000 DOI: 10.1039/b006186g Chem. Commun., 2000, 2041–2042 2041