B-silicalite

Si/Al ratio. As can be seen from the data compiled in Table 2, the transport difiusivities in sample A (HZSM-S) and B (silicalite) are virtually the same. Since the soibate molecule is nonpolar, it does not exhibit a large interaction with acid centres present in sample A. To prove this, comparative studies with olefins will be presented in a later report. 

Nitrogen adsorption is performed on calcined ZGctab and ZGdtab, as well as on reference Silicalite-1 with a particle size of about 100 nm. The three adsorption isotherms are shown in Fig.6 (black traces). Both Zeogrids exhibit a type I isotherm with a long, almost horizontal plateau, charaeteristie of a microporous material with a small specific external surface area (Fig.6a and b). Silicalite-1 also exhibits a type I isotherm with a... 

Figure 7 In situ Raman spectra of dehydrated (a) amorphous Si02, (b) silicalite, (c) Ti-silicalite (Ti/Si=0.01), and (d) Ti-silicalite (Ti/Si=0.03).

Vlugt T J H, Krishna R and Smit B 1999 Molecular simulations of adsorption isotherms for linear and branched alkanes and their mixtures in silicalite J. Phys. Ohem. B 103 1102-18... 

Bibby D M, Milestone N B and Aldridge L P 1979 Silicalite-2 a silica analogue of the aluminosilicate zeolite ZSM-11 Nature 280 664-5... 

Fig. 8.22 Schetnatic structure of the zeolite silicalite showing the straight and zig-zag chaimels. (Figure adapted fron Smit B and JI Siepmann 2994. Simulating the Adsorption of Alkanes in Zeolites. Science 264 1118-1120.)...

Infrared spectra of silicas, a) Aerosil dried at 350 C, b) Aerosil as received, c) Aerosil slurried in water and dried at 100 C, d) Silicalite as received. 

Figure 4. SEM micrographs of the silicalite-alumina composite material A cross-section of the tube. B and C magnifications of the inner surface of the tube and of the first a-AI2O3 layer.

Fig. 4 a IR spectra, in the OH stretching region, of from top to bottom, TS-1 samples (full line spectra) with increasing Ti content, from 0 (silicalite-1, dashed spectrum) to 2.64 atoms per imit cell. All samples have been activated at 120 °C. Adapted from [24] with permission. Copyright (2001) by the ACS. b Schematic representation of the preferential location of Ti atoms and Si vacancies in the MFI framework (upper part) and their interplay (lower part). Yellow and red sticks represents Si and O of the regular MFI lattice blue balls refer to Ti, and red and white balls to O and H of defective internal OH groups... 

Zhang, B.J., Davis, S.A. and Mann, S. (2002) Starch gel templating of spongelike macroporous silicalite monoliths and mesoporous films. Chemistry of Materials, 14, 1369-1375. 

Figure 1 HRSEM images (A, C + E) and AFMerror images (B, D + F) of silicalite 2. A +B is of twinned crystals and C+D of single crystals with E+F at higher magnification...

Figure 5 29Si NMR of a silicalite-1 precursor solution with a molar ratio of 25 TEOS 9 TPAOH 152 H20 a) experimental spectrum, b), c), and d) simulated spectra of large components, narrow lines and all components respectively.

Fig. 6. Raman spectra of sample 1 (Ti-free silicalite), and samples 3, and 5 (TS-1 with Ti02 wt% being 2 and 3, respectively), (a) Spectra collected with a A = 1064 nm (9398 cm-1) excitation, (b) Spectra collected with a A = 224 nm (40,984 cm x) excitation. Inset UV-DRS spectrum of sample 5. Vertical line indicates the position of the excitation wavelength A used for collecting the sample reported in part (b). Vertical dotted lines are placed at 960 cm 1. Spectra of both parts have been vertically shifted for clarity [Reprinted from Ricchiardi et al (41) with permission. Copyright (2001) American Chemical Society].

Fig. 9. (a) Infrared spectra of outgassed thin pellets of Ti-free silicalite (curve 1) and TS-1 with increasing Ti content x (curves 2-5). Spectra were normalized by means of the overtone bands between 1500 and 2000 cm-1 (not shown) and vertically shifted for clarity. The thick horizontal line represents the fwhm of the 960 cm-1 band for sample 2. By assuming that this band has a constant fwhm for any x, the absorbance W obtained is plotted as the ordinate in panel b, where the band has the same fwhm as in curve 2 (horizontal thin lines), (b) Intensity W of the 960 cm-1 infrared band (normalized absorbance units) as a function of x (full squares) and corresponding Raman counts (open squares) [Reprinted from Ricchiardi et al. (41) with permission. Copyright (2001) American Chemical Society]. 

Patton, R.L., McCulloch, B., and Nidd, P.K. (2000) Chromatographic separation of fatty adds using ultrahydrophobic silicalite. U.S. Patent 6,013,186. 

Mentzen, B.F. and Gelin, P. (1995) The silicalite/p-xylene system part 1-flexibility of the MFI framework and sorption mechanism observed during p-xylene pore-filling by X-ray powder diffraction at room temperature. Mater. Res. Bull., 30, 373-380. 

Fig. 5 (a) shows the nitrogen adsorption isotherms of aluminum hydroxy pillared clays after heat-treatment at 300-500°C. These are of the typical Langmuir type isotherm for microporous crystals. Fig, 5 (b) shows the water adsorption isotherms on the same Al-hydroxy pillared clays [27]. Unlike the water adsorption isotherms for hydrophilic zeolites, such as zeolites X and A, apparently these isotherms cannot be explained by Langmuir nor BET adsorption equations the water adsorption in the early stages is greatly suppressed, and shows hydrophobicity. Water adsorption isotherms for several microporous crystals [20] are compared with that of the alumina pillared clay in Fig. 6. Zeolites NaX and 4A have very steep Langmuir type adsorption isotherms, while new microporous crystals such as silicalite and AlPO -S having no cations in the...

Figure 2.5. An HRTEM image of the atomic structure of germanium-silicalite (GeSi04), (which is a zeolitic form of silica with Ge dopants) along the [010] direction. Larger channels are 0.55 nm in diameter, by Gai and Thomas (after Gai 1999(b)).

Figure 4.2. Effect of doping on catalyst morphology nsing SEM (a) Ge-doped silicahte and (b) Cr-silicalite.

Pyrene shown a number of photophysical features that made it an attractive fluorophore to probe the microenvironment in micellar aggregates [19]. For the peaks of pyrene PL, two important peaks at about 373 nm and 390 nm among the five dominant peaks of pyrene fluorescence were numbered as 1 and III, respectively [20]. It has been known that intensity ratio of peak 111 to I (III/I) increased as the polarity at the solubilization site of pyrene decreases. Figure 6 shows fluorescence spectra (A.ex = 310 nm) of pyrene in precursor gel containing TPA and I-IV samples denoted as (a), (b), (c), (d) and (e), respectively. The value of 111/1 of pyrene does not change under silicalite-1 gel due to no formation of micelle. However, in the Fig. 6d (sample II), III/I ratio is rapidly increased, while sample III and IV are decreased slightly again. Previously, Park et al. have reported that 111/1 ratio of pyrene for... 

Figure 2 29Si MAS NMR spectra of silicalite-1 (a) and MCM-41 (b) based molecular sieves (as = as-synthesized, c = calcined)...

Fig. 21. (a) High-resolution 29Si MAS NMR spectrum of silicalite at 79.80 MHz (82) 6SS0 free induction decays were accumulated repetition time S sec. (b) The spectrum given in (a) can be computer-simulated using the minimum number of nine Gaussian-shaped peaks, shown individually below the simulated spectrum. The areas of the peaks are, from left to right, in the ratio 0.98 2.70 2.19 2.63 10.35 1.30 1.61 1.87 0.82 (see text). 

Fig. 29. 29Si MAS NMR spectra (101) at 39.76 MHz of silicalite (Si/Al) > 4400) containing sorbed organic molecules. (A), parent material (B), containing ethanol (C), containing 1-propanol (D), containing n-decane (E), containing benzene.

Flo. 52. 27A1 MAS NMR study at 130.32 MHz of the alumination of ZSM-5/silicalite with A1C13 vapor (21 /). (a) Parent material with Si/Al > 400 (b) treated zeolite with Si/AI a 50 500 scans were acquired in each spectrum. 

The isomorphous substitution of Siiv by Ti,v was claimed by Taramasso, Perego, and Notari in 1983 for a new material with the composition xTi02(l - x)Si02 (0.0 x 0.04 M). This has the crystalline structure of silicalite-1 (or MF1) with Tilv in framework positions it was named titanium silicalite-1 or TS-1 (Taramasso el al., 1983). The occurrence of isomorphous substitution was deduced from the regular increase in unit-cell parameters with the degree of substitution and from the good agreement between the observed and calculated values of the Si—O and Ti—O distances. The same type of evidence had already been obtained by the same authors in the synthesis of crystalline microporous boron silicates, where the smaller B—O distance relative to Si—O causes a decrease in unit-cell parameters (Taramasso et al., 1980). 

Fig. II. UV-Visible reflectance spectra (Kubelka-Munk function vs. wavenumber) of (a) silicalite-1 (b) TS-1. (From Boccuti et al., 1989.)...

The pore diameter of zeolite beta is 7 A, larger than those of silicalite-1 and silicalite-2 (5.5 A). Titanium incorporated into zeolite beta reacts with molecules whose dimensions are too big to diffuse in the pores and be oxidized by TS-1 or TS-2. The drawback is that zeolite beta must contain Al3+ to crystallize, and this imparts strong protonic acidity to the solid, with the consequence that secondary acid-catalyzed reactions also take place. However, the acidic properties can be neutralized in several ways and highly selective oxidations can be carried out on Ti-beta (Section V.C.3.b). 

Substituted B-phenylpropiophenones on Silicalite. We have recently shown that the lifetime of 8-phenylpropiophenone triplets is rather insensitive to substitution in the 8-phenyl ring (19). We have suggested that this insensitivity reflects the fact that triplet decay is predominantly controlled by molecular motion i.e. by how rapidly a molecule can achieve a conformation suitable for Intramolecular deactivation. 

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