Zeolite Nanoclusters Coated onto the Mesopore Walls of SBA-15 Trong-On Do, † Andrei Nossov, ‡ Marie-Anne Springuel-Huet, ‡ Celine Schneider, § Jeremy L. Bretherton, § Colin A. Fyfe, § and Serge Kaliaguine* ,† Department of Chemical Engineering, LaVal UniVersity, Quebec G1K 7P4 Canada, UniVersite ´ Pierre et Marie Curie, Laboratoire SIEN, 4, place Jussieu 75252 Paris, France, and Department of Chemistry, UniVersity of British Columbia, 2036 Main Mall, VancouVer, British Columbia V6T 1Z1, Canada Received June 26, 2004; E-mail: serge.kaliaguine@gch.ulaval.ca Hydrothermal stability and acidity are both essential for the application of mesoporous materials in catalysis. 1,2 Several ap- proaches have been aimed at improving these properties; 3-8 for example, hydrothermally stable and strongly acidic mesoporous aluminosilicates have been assembled using protozeolitic seeds. 5,6 A recent study from our group showed that the coating of protozeolitic nanoclusters onto the surface of preformed mesos- tructured aluminosilicates greatly improved both their acid strength and hydrothermal stability. 7,8 These resulting zeolite-coated meso- porous aluminosilicates (noted ZCMeso-AS) were found to be stable to exposure to 20% water vapor for 24 h at 800 °C and in boiling water at 100 °C for at least 5 days and to exhibit acidities comparable to those of zeolites. It is thought that these properties of the highly acidic ZCMeso-AS are due to the zeolitic nature of their mesopore wall surfaces. 7 These features overcome the limitations of conventional zeolites and mesoporous materials as catalysts. In a previous paper, 7 we have shown that there are significant decreases in mesopore diameter (from 70 to 54 Å), in surface area (from 800 to 465 m 2 g -1 ), and in mesopore volume (from 1.56 to 0.78 cm 3 g -1 ) of a mesoporous aluminosilicate SBA-15 sample (designated as PMesoAS in ref 7, atomic Si/Al ) 65) after coating with ZSM-5 seeds (designated as ZCMesoAS, 7 atomic Si/Al ) 50). The coated sample shows a FTIR band at ∼550 cm -1 (characteristic of the five-membered ring units in the pentasils) which is not present in the parent SBA-15 sample. Taken together, these observations indicated that zeolite nanoclusters were located inside the mesopore channels. 7 However, no micropore volume of zeolite was detected by nitrogen adsorption isotherms. XRD diagrams of the coated samples show no zeolite peaks in the 2θ range of 10-50°, indicating that the coating contains no crystals with dimensions greater than ∼50 Å. Similarly, no XRD reflections characteristic of zeolite crystals were observed for the materials assembled from zeolite seeds. 5,6 In the present paper, we provide additional evidence which confirms that zeolite nanoclusters are coated on the mesopore surface of the host, using 129 Xe NMR as a sensitive technique for probing the internal pore structure 9 as well as ultrahigh-field 27 Al MAS and MQMAS (750 MHz for 1 H) NMR for quantifying the multiple aluminum environments in these materials. 10 The 129 Xe NMR spectra of the parent SBA-15 sample (e.g., PMesoAS) at various pressures show two lines at ∼70 and 0 ppm corresponding to the xenon in the mesopore channels and in the gas phase, respectively (Figure 1A). The chemical shift of the line from the adsorbed xenon slightly decreases as it is the case for Xe adsorbed in mesoporous systems (ca. 3 ppm as the xenon pressure changes from 40 to 820 Torr). 9 However, the ZSM-5-coated sample (e.g., ZCMesoAS) shows an additional signal at higher chemical shift increasing from 109 to 125 ppm for the same pressure range as above, which is attributed to the xenon adsorbed in the microporous channels of ZSM-5 (Figure 1B). This intensity corresponds to ∼2 wt % of zeolite ZSM-5. Figure 1a,b, shows that increasing the Xe pressure yields broader resonance signals, an effect which is ascribed to an increased exchange between Xe populations N gas , N meso , and N micro . As shown by the spectra and deconvolutions in Figure 2, various aluminum environments in these samples are detected by ultrahigh- field 27 Al MAS NMR spectroscopy. NMR experiments were carried out at 750 and 800 MHz for 1 H on spectrometers at the Pacific Northwest National Laboratory, Richland, Washington. 10 For the parent sample, (Figure 2A), two distinct aluminum environments are present: a broad peak at 64.4 ppm typical of tetrahedral aluminum in amorphous materials (considering that the high-field yields lower experimental shifts by partially removing the quadru- polar interaction of 27 Al) and a second broad peak at 9.9 ppm due † Laval University. ‡ Universite ´ Pierre et Marie Curie. § University of British Columbia. Figure 1. 129 Xe NMR spectra of (A) parent SBA-15 and (B) ZSM-5-coated SBA-15 at various xenon pressures. Figure 2. 27 Al MAS NMR spectra at 208.43 MHz (18.8 T, 800 MHz for protons) of: A) parent SBA-15, B) ZSM-5 coated SBA-15 after calcination, (C) NaY-coated SBA-15. Pulse angles of approximately 12° were used to ensure even excitation of all the nuclei. Published on Web 10/15/2004 14324 9 J. AM. CHEM. SOC. 2004, 126, 14324-14325 10.1021/ja0462124 CCC: $27.50 © 2004 American Chemical Society