In this paper, a new delaminated mesoporous material was prepared by swelling the lamellar phyllosilicate Magadiite using cetyltrimethylammonium bromide and tetrapropylammonium hydroxide solution, followed by delamination under the cavitation of ultrasonic treatment. Various characterization tools including XRD, N2 adsorption, NMR, IR, SEM and TEM were employed to observe its structure and morphology. XRD results show that the delaminated material has no long-range crystalline order. Furthermore, not only high surface area is obtained, but almost half of it is external surface. The observation for the morphology further reveals that it is made up of the random stacking of single or few layers. All these characters show that this delaminated mesoporous material meets the requirements for application as support in the hydrotreatment of heavy molecules.

NMR measurements on the two naturally abundant isotopes of thallium and on fluor have been made in the defect pyrochlore TINb2OsF. An Arrhenius activation energy of 0.08 eV was obtained from the temperature dependence of the 205T1 absorption linewidth. CW data indicated the presence of the electron-nuclear magnetic interactions. The spin-lattice relaxation times showed two motions of T1 + ions with the activation energies of 0.25 eV and 0.14 eV. These relaxation times were interpreted with the exchange and chemical shift interactions.

The electric-field gradients (EEG) in the supercage of HY, steam-dealuminated Y (STY) and lanthanum-exchanged Y zeolites (LaY) have been quantified using the difference in chemical shift delta(CS)(Xe-131) - delta(CS)(Xe-129) of the two NMR-observable isotopes Xe-131 and Xe-129. The first, with spin I = 3/2, is sensitive to EGF whereas the second, with I = 1/2, is not. The EEG values are 15.75x 10(19) V/m(2) for HY, 14.30x 10(19) V/m(2) for STY and 12.40x 10(19) V/m(2) for LaY.

Numerous NMR techniques are available for the study of nuclei with spin I greater than or equal to 1. These nuclei interact with their surrounding electric field gradient, which depends on the symmetry of the crystallographic site. Spurious (or piezoelectric) signals, due to the piezoelectric and ferroelectric properties of a LiNbO3 crystal and generated by the vibration of the macroscopic electric dipole of the crystal, have been observed with the one-pulse sequence and cancelled using a composite-pulse sequence. The suppression of these piezoelectric signals by this sequence is illustrated by lithium-7 (I = 3/2) nuclei. Java applets available in our web site www.pascal-man.com for the determination of quadrupole parameters from one-dimensional nutation method are also presented. (C) 2004 Academie des sciences. Published by Elsevier SAS. All rights reserved.

The increasing development and application of the multiple-quantum MAS NMR for half-integer quadrupole spins has led to various RF pulse sequences for improving the excitation of multiple-quantum coherences and their conversion to single-quantum coherences. As a result, several conventions for labeling the Fl dimension of a 2D MQ-MAS spectrum appear in the literature. The corresponding relations for extracting the isotropic chemical shift, the quadrupole coupling constant, and the asymmetry parameter from experimental data are not always provided. We analyze these various conventions systematically and propose a new one, similar to that introduced by J.-P. Amoureux and C. Fernandez (2000, Solid State NMR 10, 339-343). These various conventions are illustrated with 27Al (I = 5/2) nuclei in aluminum acetylacetonate Al(CH3COCHCOCH3)3. Another experimental problem often met, the aliasing of peaks in the 2D spectrum, is analyzed and illustrated with 27Al (I = 5/2) in NH4Y zeolite and 23Na (I = 3/2) in sodium pyrophosphate Na4P2O7.

A detailed solid state NMR study of molecular aluminophosphates is presented. The crystallographic structures of [Al4(HPO4)4(C2H5OH)12]Cl4·4C2H5OH (compound 1) and [Al4(HPO4)4(C2H5OH)12]Br4·4C2H5OH (compound 2) were obtained at low temperature. 13C CP MAS NMR dynamics were carefully studied: non-exponential growth of magnetisation was observed for 13C CP even for moderately coupled 13CH3 groups. This approach was extended for the first time to 31P CP MAS NMR. Variable contact time as well as inversion recovery cross polarisation (IRCP) experiments showed unambiguously that the 1H → 31P magnetisation transfer was also not exponential. The 31P IRCP MAS experiment proved to be a powerful tool for the study of complex amorphous materials, allowing editing of the spectra. Variable contact time experiments under fast MAS led to the observation of strong dipolar oscillations. The subsequent analysis of the CP data in the frequency domain led to the direct accurate determination of 31P–1H distances. This approach can be used as an alternative method for the measurement of distances in solid state NMR. 27Al NMR quadrupolar parameters for 1 and 2 were derived by using several static and MAS techniques, in both time and frequency domains. The time domain response to a two-pulse sequence led to the very unusual observation of multiple quadrupolar Solomon echoes. The spectroscopic data related to 1 and 2 are a good starting point and pertinent tools for the study of more complex derivatives.

The electric-field gradients in the supercage of HY and steam-dealuminated Y zeolites have been quantified using one-dimensional nutation NMR applied to physisorbed Xe-131. Their values are 1.25 and 0.81(.)10(19) V(.)m(-2), respectively. The composite-pulse sequence used to detect Xe-131 signal also cancels the ringing signals from the NMR probe head. The fitting program for extracting the quadrupole coupling constant from the nutation NMR data is available in the web site http:///www.pascal-man.com. (C) 2001 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.

Spurious signals such as the piezoelectric signal from a ferroelectric crystal or the ringing signal from the NMR probe head tuned for low gyromagnetic ratio nuclei are often observed in pulsed NMR. Both signals are cancelled using the Hahn echo sequence with appropriate phase cyclings. The present paper applies a composite-pulse sequence to cancel the ringing signal. The main advantage of this sequence over the Hahn echo sequence is in the simplicity of optimizing the line intensity: the optimization of only one pulse duration for this sequence but of two pulse durations and the interpulse delay for the Hahn echo sequence. We are interested in half-integer quadrupole spins (I = 3/2, 5/2, 7/2, and 9/2), which means that we must consider the first-order quadrupole interaction during the pulses. For simplicity, we deal mainly with spin I = 3/2 nuclei. Since the central-line intensity depends on the ratio of the quadrupole coupling constant (QCC) to the amplitude of the RF pulse, we can determine the QCC from a featureless lineshape by fitting the variation of the experimental central-line intensity for increasing pulse duration with theoretical results. Contrary to the one-pulse sequence where the central-line intensity is proportional to the pulse duration if the latter is short, there is no such condition with the composite-pulse sequence. In other words, this sequence does not allow us to quantify the relative spin populations in powders. The size of the sample must be much smaller than that of the RF coil in order for the RF magnetic field to become homogeneous for the sample. We used (87)Rb (I = 3/2) in an aqueous solution of RbCl and in RbNb2O5F powder, (131)Xe (I = 3/2) of xenon gas physisorbed in Na-Y zeolite, and (23)Na (I = 3/2) in two well-known powders (NaNO3 and NaNO2) to support our theoretical result.

Solid-state modification of Y zeolites (NaY or LaNaY) with MnCl2·xH2O leads to three successive phenomena depending on the thermal treatment temperature, Tt: maximum halide insertion into the supercages at low temperature (433 K), exchange with Na+ and NH4+ in the zeolites at 613–793 K and solid–solid reactions with the appearance above 1073 K of new crystalline phases, most of which are identified. The results are compared with those for V2O5, MoO3 and Sb2O3.

Mixtures of Y zeolites (NaY or LaNaNH4Y) and manganese chloride tetrahydrate are treated in air at atmospheric pressure. Depending on the treatment temperature, T-t, three successive processes can occur: maximum halide insertion into the supercages at low temperature (503 K); maximum cation exchange at 683 K and solid-solid reactions with the appearance of new crystalline phases at ca. 1073 K.

Borosilicalites having the MFI structure (B-ZSM-5) exhibit correlations of the 129Xe nuclear magnetic resonance (NMR) chemical shift at low xenon coverage and of the adsorption coefficient with the lattice boron content. Both these correlations show a discontinuity at around one boron atom per unit cell. Since xenon is particularly sensitive to collisions with zeolite surfaces, these results suggest the existence of two boron concentration ranges for which the surface properties are different. One may assume that the effective electric field related to one site decreases when the concentration exceeds one boron atom per unit cell. To monitor the incorporation of boron into the B-ZSM-5 lattice one can use 129Xe NMR spectroscopy in addition to other characterization methods.

Thermal treatment of antimony oxide mixed with NaY or LaNaY zeolite in a well-defined ranges of temperature and composition in air at atmospheric pressure causes the oxide to migrate into the cavities of the zeolite lattice. The maximum degree of insertion is of the same order of magnitude as for V2O5 or MoO3 and is higher for LaNaY than for NaY. This difference in the degree of insertion in the two zeolites can be attributed to the space left vacant in the supercages by the migration of La3+ ions into the sodalite cages and hexagonal prisms of LaNaY (during calcination) and also by its acidic character. In contrast to vanadium and molybdenum oxides, which are somewhat acidic and collapse the crystalline structure of Y zeolite at a relatively low temperature (730 K) for compositions with R(V,Mo) > 0.4 (R(V,Mo) = number of V or Mo atoms per SiO4 or AlO4 tetrahedron), antimony oxide, which is amphoteric, begins to degrade it only at 930 K and R(Sb) = 0.2 for NaY and above 830 K and R(Sb) 0.4 for LaNaY. When the temperature is over 1,060 sb K and R(Sb) = 0.4, solid-solid reactions lead to the appearance of new phases. Interactions and reactions in the solid state have been studied by X-ray diffraction, Xe adsorption, Si-29 MAS n.m.r., and Xe-129 n.m.r. spectroscopy. (C) Elsevier Science Inc. 1997.

The response of a spin 7/2 system subject to a first-order quadrupolar interaction and excited by two in-phase pulses separated by time delay tau is calculated ignoring high frequency terms. The results obtained are valid for any ratio of the quadrupolar coupling to the amplitude of an RF pulse. It is shown here that single- and multiple-quantum coherences developed during the first pulse can be detected at the end of the second pulse. Other pulse sequences with various phase cycling are also discussed. The results are applied to V-51 nuclei in a single ferroelastic crystal of BIVO4.

The response of a spin72in solids, subject to a first-order quadrupolar interaction, to a spin lock pulse sequence is calculated. The results are valid for any ratio of quadrupolar coupling, ωQ, to the amplitude, ω1, of the RF pulse. It is shown here that the measurements of the central line intensity as a function of the second pulse length can be used for the determination of quadrupolar parameters using various phase cycling techniques. It is proven that the DQ coherences developed during the first pulse can be selectively detected.

The structures of complexes obtained by the reaction of alizarin (C14H8O4) and Al3+ in basic media depend upon the reaction solvent and the nature of the base. With aqueous or methanolic solutions of sodium hydroxide a binuclear complex [Al-2(mu-OH)(2)(C14H6O4)(4)(Na)(4)(H2O)(4)] was obtained, which is stable as the tetrahydrate and is observed even in the gas phase by electrospray mass spectrometry. With potassium hydroxide the monohydrate form is obtained. These two products are distinguishable by Al-27 NMR in the solid state by means of their chemical shifts (+23.1 and 0.0 ppm) and their linewidths Delta nu(1/2) (1200 and 4000 Hz). The chemical shifts of these binuclear complexes or similar derivatives are discussed in relation to possible chelation of the four molecules of water with alizarinate entities according to the bulk of the cation. The results are illustrated by two types of structure, named 'closed structure' (with strongly chelated H2O molecules and dibenzene sandwich Na+) and 'open structure'.

Solomon echoes are calculated for spin 7/2 in solids taking into account the first-order quadrupolar interaction while the pulses are on. The computation is performed using the algebraic computer program ‘MAPLE’. Fifteen echoes are predicted and the amplitude of each echo is calculated. Each satellite transition produces five echoes whereas no echo is detected for the central transition. Among these echoes, six are ‘forbidden’ which are a result of the refocusing of exclusively multiple quantum coherences which are developed during the first pulse. These echoes cannot be predicted by a calculation based upon ‘hard’ pulse excitation. The results are valid for any ratio of the quadrupolar coupling to the frequency of the RF field (ωQ/ω1).

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

SAPO-34 (chabasite structure) is studied with regard to decomposition of the template [tetraethylammonium hydroxide (TEAOH) or morpholine] and subsequent hydration-dehydration cycles over a period of few hours up to 2 years. XRD, IR, Al-27 and Si-29 MAS NMR, and N-2 adsorption an used to characterize the related structural changes. The template decomposition results into shifts in Al-27 and Si-29 MAS NMR peaks reflecting its interaction with the framework. Hydration of the template-free materials leads at room temperature to a breaking of Si-OH-Al bonds, giving a partial loss of crystallinity and the formation of Q(1), Q(2), and Q(3) Si species (Si(OT)(n)(OH)(4-n)). Dehydration of the materials after about 1 or 2 day hydration gives reversibly the. initial crystallinity, the Si environment, and the porosity for the template-free materials. Long-term hydration, up to 2 years, shows that zeolites synthesized with morpholine as a template do not recover their full crystallinity and eventually none of their porosity. By contrast, TEAOH materials-are more stable, keeping up to 80% of the starting crystallinity and 70% of their porosity. The influence of the template is correlated to the formation, during synthesis of Si islands with TEAOH, while morpholine gives a larger part of isolated Si. This restricts in the TEAOH sample the number of Si-OH-Al bonds, i.e., of points where water attacks the framework.