Zeolite spinning sidebands

In Table 2, the A chemical shifts of the carbon atoms of alkoxy species attached to zeolite framework oxygen atoms are summarized. In general, the spins of surface alkoxy species are characterized by relatively long T times (2-5 s), an efficient CP, and broad spinning sideband patterns. The adsorption and... 

Fig. 18. C CP/MAS NMR spectra of zeolite HY (/isi/mai = 2.7) recorded after a continuous injection of CHPCH2OH into the MAS NMR rotor reactor at room temperature and subsequent purging with dry nitrogen at room temperature (a) after a subsequent purging with dry nitrogen at 453 K (b) and after water had been injected into the MAS NMR rotor reactor at room temperature (c). The CP/ MAS NMR spectra of ethylated zeolite Y (Cl l/f l F-Y) were recorded after thermal treatments at 52 K (d) and 623 K (e). Asterisks denote spinning sidebands.

Fig. 20. H MAS NMR spectra of zeolite HZSM-5 (nsi/ Ai = 21.5) before (a) and after (b) adsorption of 0.33mmol acetone-d per gram. In (c) and (d), the ll MAS NMR spectra of zeolite D,HZSM-5 recorded before and after loading, respectively, with 0.34mmol acetone- C-2 per gram of zeolite are shown. The inset (e) is the C MAS NMR spectrum of the sample in (d). Asterisks denote spinning sidebands. Reproduced with permission from (J33). Copyright 2003 The Royal Society of Chemistry.

Fig. 32. CF MAS NMR spectra recorded during the conversion of C-enriched methanol ((U/ F = 100 gh/mol) on calcined zeolite HY (nsi/ Ai = 2.7) at reaction temperatures of 393 K (a), 433 K (b), and 473 K (c). The spectra on the left-hand side were obtained with MAS NMR and proton decoupling (HPDEC), and the spectra on the right-hand side were recorded with the CP technique. Asterisks denote spinning sidebands. Reproduced with permission from (74). Copyright 2001 American Chemical Society.

Fig. 35. C MAS NMR spectra of methylated zeolite Y ( (Ils-Y) recorded after loading with toluene (natural abundance of ( -isotopes) and thermal treatments at temperatures from 298 (a) to 493 K (e). Asterisks denote spinning sidebands. Reproduced with permission from (263). Copyright 2003 American Chemical Society.

Fig. 37. C CF MAS NMR (left) and UV/Vis (right) spectra of a dealuminated zeolite HZSM-5 recorded during conversion of ( -enriched methanol (W/F = 25gh/mol) at 413 K for 2h (a), during a subsequent conversion of T l U = T l U (W/F = 10 g h/mol) at 413 K for 1 h (b), and during conversion of V H2 = V H2 (W/F= 10 g h/mol) at 413 K on a fresh catalyst for 2 h (c). Asterisks denote spinning sidebands. The narrow peaks at ca. 500 nm in UV spectra were caused by the equipment. Reproduced with permission from 168). Copyright 2004 The Royal Society of Chemistry.

Fig. 31. Representative 188-MHz l9F NMR spectra of p-fluoroaniline (top) andp-fluoroni-trobenzene (bottom) obtained in zeolites HY and HZSM-5. Spinning sidebands are denoted by asterisks. Spectra were acquired (several thousand scans) using magic angle spinning (4-mm rotors), cross polarization (2 ms), and proton dipolar coupling. (Reprinted with permission from Nicholas et al. (82). Copyright 1995 American Chemical Society.)...

Figure 4) 1-H-MAS NMR spectra of a non steamed H-ZSM5 zeolite. A) before coking B) after coking, a) non-acidic OH groups b) Bronsted acid OH groups. spinning sidebands (reproduced with the permission from reference 15).

Detailed calculations of the spinning sidebands in DAS spectra have been carried out using average Hamiltonian and irreducible tensor approaches (Sun et al. 1992). In DAS spectra the sideband intensities and their moments depend on the relative rotor phase between the two evolution periods. The sideband intensities additionally depend on the ratio of the time spent at each angle. The 2D O DAS spectrum of zeolite Sil-Y (Figure 3.22) shows three lines in the ratio 2 1 1 (Bull et al. 1998). Simulation of the anisotropic slices from the O 2D DAS spectrum for each peak allows extraction of xq and t] for each resonance. 

To obtain a high-resolution spectrum free from the unwanted CT CT peak, the third method proposed uses half-rotor synchronisation, instead of full-rotor period synchronisation, during [40]. The increment in (or kt for split-ti experiments) is set to half the rotor period, thereby doubling the isotropic spectral width (Fi=2Vj., where Vj. is the MAS rate). This means that two sets of STn CT resonances will be observed, a centreband and a spinning sideband. In principle, the latter will be well resolved from the CT CT diagonal peaks, which in general do not display any sidebands in Compared with a full-rotor synchronisation, the S/N ratio is reduced by a factor of two and the experimental time is doubled. As an example. Fig. 13a shows the STMAS spectrum of zeolite scolecite. 

The interaction of probe molecules with acidic OH groups is also studied, " even though the detail is not described in this report. Moreover, the spinning sidebands analysis in H MAS NMR offers the information on the distance between the bridging OH groups and aluminium ions in the zeolite framework. - ... 

A 18° fripDangle was employed to make the Al yfi9n J intensities as quantitative as possible. In calculating A1V1/A11V ratios, it was assumed that the spinning sidebands (SSB) were of equal intensities, as observed in the fresh zeolite samples. 

Na, Al, and Si. The observed values of chemical shifts and line widths are = -12.5, 5 = 58.6, 5gj = -89.4 ppm and Av = 490, Av - 300, Avgj = 100 Hz, respectively. On partial replacement of Al by Fe , whereas no detectable change in the chemical shift values was observed for these three probe nuclei, the line width for both Na and Si showed significant and systematic increase, the variation in Av was found to be relatively small suggesting that the Al - 0 - Fe type interaction does not exist in the tetrahedral frame work of these zeolite samples. Based on the Fe Mossbauer effect and NMR spectra it is inferred that Fe ions are replacing Al ions in the zeolite network. The intensities of observed spinning sideband spectra have been analysed to get the values of the components of the chemical shift anisotropy. 

The spectrum for unsubstituted zeolite samples gave a sharp line with chemical shift 5 = 58.9 ppm and a line width of 300 Hz. with a very feeble these side bands and the width of the isotropic signal showed a systematic increase in their values. The Fe substitution did not affect the chemical shift values From the intensity analysis of the spinning sidebands, the values of the components of the chemical shift tensor aji, the asymmetry parameter ti and the anisotropy parameter 5 have been calculated by following the graphical method developed by Herzfeld (10) and the values are listed in table 1. 

Figure 14 In situ C MAS NMR study of the reactions of methyl iodide- C on zeolite CsX. Methyl iodide (-15 ppm) was partially converted to a framework-bound methoxy (58 ppm) upon adsorption at 298 K. Ethylene (120 ppm) formed between 448 and 498 K, and oligomerized and cracked to a mixture of hydrocarbons at 523 K. denotes spinning sideband.

Fig. 13. Comparison between the conventional (top) and isotropic (bottom) MAS NMR spectra of multicomponent mixtures. Asterisks corre nd to spinning sidebands. The sodium system contained approximately equimolar mixtures of Na2S04 and Na2C204 the aluminium system was a mixture of CaA zeolite and Linde-13X faujasite (from Frydman and Harwood with permission).

Fig. 21. Cs MAS NMR spectrum of a dehydrated 72% cesium-exchanged zeolite Y (a), the simulated spectrum (b), the components (c), and spinning sidebands ( ) [187]...

The MAS NMR spectra of dehydrated and unloaded zeolites consist of a narrow central line and sharp spinning sidebands at room temperature. Therefore, the correlation time of the hydroxyl protons must be large compared with the... 

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