The influence of dealumination of two commercial amorphous silica-aluminas (ASAs) with acetylacetone on their textural properties, acidity and catalytic activity was studied by N-2-sorption, NH3-TPD, FTIR of adsorbed pyridine as well as H-1 and Al-27 MAS NMR. Acetylacetone treatment increases the pore volume and surface area (+20 ->+30%) of commercial ASA without changing the pore size. More than half of the Al species are extracted from ASA but the total acidity is preserved or even slightly increased (for the ASA with higher Al content). The percentage of acidic Al is increased by a factor 2. Dealumination results in a better access to acid sites and an increase of medium Bronsted acid sites (BAS), leading to a 1.5 higher catalytic activity for 3,3-Dimethyl-1-butene (33DMB1) isomerization.

The main common idea of two conference papers delivered at OMEE-2017 was to demonstrate an importance of the speciation level knowledge in modern adsorption materials science. In order to prove this, two groups of adsorptive materials were used: three samples of Mg-Al-CO3 layered double hydroxides produced by different synthesis methods and ten samples of Fe-Ce oxide-based composites with various ratios of Fe-to-Ce. In both cases of studies, it was not possible to find direct correlation between adsorptive performances of the materials and their structural properties obtained by conventional characterisation techniques. However, anion adsorptive removals of each group of inorganic composites correlated with their structural properties studied on the level of speciation. It was shown that strong anion removal potential of Mg-Al-CO3 layered double hydroxides was associated with richness in speciation of chemical elements (Mg, Al) and interlayer anions (CO32-) as well as with generous hydration. Adsorptive performances of inorganic anion exchangers based on Fe-Ce hydrous oxides were explained by simulation extended X-ray absorption fine structures simulation. The best anion removers were found to be those Fe/Ce oxide-based composites whose Fe outer shells were formed from backscattering oscillations from both O and Fe atoms.

This work is the first report that critically reviews the properties of layered double hydroxides (LDHs) on the level of speciation in the context of water treatment application and dynamic adsorption conditions, as well as the first report to associate these properties with the synthetic methods used for LDH preparation. Increasingly stronger maximum allowable concentrations (MAC) of various contaminants in drinking water and liquid foodstuffs require regular upgrades of purification technologies, which might also be useful in the extraction of valuable substances for reuse in accordance with modern sustainability strategies. Adsorption is the main separation technology that allows the selective extraction of target substances from multicomponent solutions. Inorganic anion exchangers arrived in the water business relatively recently to achieve the newly approved standards for arsenic levels in drinking water. LDHs (or hydrotalcites, HTs) are theoretically the best anion exchangers due to their potential to host anions in their interlayer space, which increases their anion removal capacity considerably. This potential of the interlayer space to host additional amounts of target aqueous anions makes the LDHs superior to bulk anion exchanger. The other unique advantage of these layered materials is the flexibility of the chemical composition of the metal oxide-based layers and the interlayer anions. However, until now, this group of "classical" anion exchangers has not found its industrial application in adsorption and catalysis at the industrial scale. To accelerate application of LDHs in water treatment on the industrial scale, the authors critically reviewed recent scientific and technological knowledge on the properties and adsorptive removal of LDHs from water on the fundamental science level. This also includes review of the research tools useful to reveal the adsorption mechanism and the material properties beyond the nanoscale. Further, these properties are considered in association with the synthetic methods by which the LDHs were produced. Special attention is paid to the LDH properties that are particularly relevant to water treatment, such as exchangeability ease of the interlayer anions and the LDH stability at the solid-water interface. Notably, the LDH properties (e.g., rich speciation, hydration, and the exchangeability ease of the interlayer anions with aqueous anions) are considered in the synthetic strategy context applied to the material preparation. One such promising synthetic method has been developed by the authors who supported their opinions by the unpublished data in addition to reviewing the literature. The reviewing approach allowed for establishing regularities between the parameters: the LDH synthetic method. structure/surface/interlayer. removal. suitability for water treatment. Specifically, this approach allowed for a conclusion about either the unsuitability or promising potential of some synthetic methods (or the removal approaches) used for the preparation of LDHs for water purification at larger scales. The overall reviewing approach undertaken by the authors in this work mainly complements the other reviews on LDHs (published over the past seven to eight years) and for the first time compares the properties of these materials beyond the nanoscale.

NMR Hamiltonians are double contraction of two spherical rank-2 tensors, their space parts are represented by a spherical tensor and their spin parts are composed of spherical tensor operators. The comprehension of modern NMR experiments is very often based on the rotation of these tensors. We present the active and passive rotations in a progressive way from position vector to spherical tensor operator via space function, spherical harmonic, and vector operator. The passive rotation of a physical quantity is described by the rotation of coordinate system. Both the left- and right-handed rotation conventions are applied whereas the right-handed rotation convention is mainly used in the literature. Throughout the article, we explore the equivalence between the active rotation of a physical quantity in one direction and the rotation of the coordinate system in the opposite direction. The article presents redundant mathematical demonstrations between active and passive rotations, but they clarify the meanings of some important expressions not well developed in the literature.

De nombreuses experiences de RMN, en particulier en phase solide, exigent de longues heures d’acquisition, du fait de la complexite de l’echantillon ou tout simplement de la faible sensibilite intrinseque de cette technique. Dans certains cas, il est meme necessaire de continuer l’experience pendant une ou plusieurs semaines afin d’avoir un signal exploitable, d’autant plus que le rapport signal sur bruit croit comme la racine carree du nombre de scans. De telles durees entrainent des contraintes importantes, que ce soit en termes d’occupation des appareils, de stabilite de l’echantillon, ou encore de stabilite de l’equipement. Afin de reduire les temps d’experience necessaires, une technique mathematique de debruitage des spectres, appelee Singular Value Decomposition (SVD)1 a ete implementee sous la forme d’un applet java utilisant la puissance des cartes graphiques Nvidia2 (cf figure 1). En effet, les cartes graphiques actuelles sont de veritables calculateurs pouvant effectuer de nombreuses tâches en parallele et ainsi diminuer considerablement la duree du calcul a faire. Dans ces conditions, il devient tout a fait envisageable de retirer le bruit d’un spectre en quelques secondes. Cette application facilement utilisable permettra sans doute, en lien avec les autres techniques developpees de par le monde, d’augmenter encore la sensibilite de la RMN et de repondre a des problematiques toujours plus complexes.

We present a post-processing method that decreases the NMR spectrum noise without line shape distortion. As a result the signal-to-noise (S/N) ratio of a spectrum increases. This method is called Cadzow enhancement procedure that is based on the singular-value decomposition of time-domain signal. We also provide software whose execution duration is a few seconds for typical data when it is executed in modern graphic-processing unit. We tested this procedure not only on low sensitive nucleus (29)Si in hybrid materials but also on low gyromagnetic ratio, quadrupole nucleus (87)Sr in reference sample Sr(NO3)2. Improving the spectrum S/N ratio facilitates the determination of T/Q ratio of hybrid materials. It is also applicable to simulated spectrum, resulting shorter simulation duration for powder averaging. An estimation of the number of singular values needed for denoising is also provided.

NMR Hamiltonians are anisotropic due to their orientation dependence with respect to the strong, static magnetic field. They are best represented by product of two rank‐2 tensors: one is the space‐part tensor T and the other is the spin‐part tensor A . We reformulated the dot product of Cartesian tensors and the dyadic product of spherical tensors in NMR Hamiltonian as the double contraction of these two tensors. As the double contract has two definitions (double inner product and double outer product of two rank‐2 tensors), there are two sets of spherical tensor components in terms of Cartesian tensor components for any rank‐2 tensor, two Cartesian Hamiltonians, and two spherical Hamiltonians. We succeeded in determining the spherical components of tensors A and T that verify the Cartesian Hamiltonian defined by the double inner product of two rank‐2 tensors and the spherical Hamiltonian defined by the double outer product of two rank‐2 tensors. In particular, we established the spherical components of space‐part tensor T in terms of Cartesian tensor components provided by Cook and De Lucia. Throughout the article, Wigner active rotation matrix is used to illustrate the active rotation of spherical vector, spherical harmonics, and spherical tensor as well as the passive rotation via their rotational invariants. © 2014 Wiley Periodicals, Inc. Concepts Magn Reson Part A 42A: 197–244, 2013.

A tremendous number of studies have examined layered double hydroxides (LDH) for their technological applications in the ion exchange removal of toxic ions, recovery of valuable substances, catalysis, CO2 capture, as a layered host for storage/delivery of biologically active molecules, additives to plastics and building materials, and other functions. Numerous publications always conclude that the materials (prepared, as a rule, using the oldest synthesis method) are very promising for each investigated application; however, the main chemical industries producing these materials advertise them mainly (or only) as plastic additives. The authors performed extensive research using many of the appropriate methods to compare the structure, surface and adsorptive properties of three Mg–Al LHDs produced by advanced synthesis methods. One industrial sample (by Sasol, Germany) prepared by the alkoxide sol–gel method and two novel Mg–Al LDHs synthesised in-house by alkoxide-free sol–gel and hydrothermal precipitation approaches were investigated. Reasons for the very different adsorptive selectivity of the three LDHs towards arsenate, selenate, phosphate, arsenite and selenite have been provided, highlighting the role of speciation of the interlayer carbonate, aluminium, magnesium, interlayer hydration and moisture content in the adsorptive selectivity towards each toxic anion. This work is the first report presenting the regularities of the LDHs structure, surface and anion exchange properties as a function of their syntheses method. It establishes the links to potential technological applications of each investigated LDH and explains the necessary properties required to make the technological application cost-effective and efficient. The paper might accelerate industrial applications of these advanced materials.

Euler angles are commonly used for orientating a coordinate frame relatively to another or for describing the rotation of rigid body about a fixed point. Unfortunately, there is no standard notation for Euler angles and rotation axes in composite rotation matrices. Two types (passive and active) of rotation are possible; each of them can be performed either in rotated or in fixed frames. We suggest a notation harmonization for composite rotation matrices. To this end, we first gather the conditions and conventions available in the literature. Second, the matrices of elementary rotation about basis vectors are identified because they participate in the construction of composite rotation matrices. They allow us to determine the type of composite rotation matrix. Third, we introduce the Euler angles during the description of two composite rotations of bases. This permits us to anticipate the type of the resulting composite rotation matrices. It results the central convention that suggests us to order Euler angles and rotation axes in the definition of composite rotation matrix in the same way as the three elementary rotation matrices. This convention is not always applied in the literature. Fourth, we confirm our anticipation using composite rotation of vector. Fifth, this central convention permits us to define the multiplication order of two composite rotation matrices straightforward. Finally, we apply the matrices of composite active rotation about fixed axes to X-pulse, spin-lock pulse, and magnetization inversion pulses. (c) 2012 Wiley Periodicals, Inc. Concepts Magn Reson Part A 40A: 215252, 2012.

Our recent method based on the use of web tools (XML and XSLT) for constructing cogwheel phase cycles is extended to the selection of two symmetrical coherence transfer pathways in the case of an amplitude-modulated z-filter MQMAS sequence. For all spins (I=3/2, 5/2, 7/2 and 9/2) and all MQ experiments we compare cogwheel phase cycling with the traditional "nested" phase cycling. The principal difference in the number of phase cycling steps lies in the use of digitizer phase. For nested phase cycling, this number depends on the use of reference receiver phase or digitizer phase, while cogwheel phase cycling does not. As an illustration we consider the case of a+/-3QMAS experiment for spin I=7/2 system applied to cobalt-59 in [Co(NH3)6]Cl3 powder. We also explore the selection of two non-symmetrical coherence transfer pathways in the case of an amplitude-modulated shifted-echo MQMAS sequence.

In solid-state NMR, multiple-quantum MAS (MQMAS) and satellite-transition MAS (STMAS) experiments are well-established techniques to obtain high-resolution spectra of half-integer quadrupolar nuclei. In 2004 and 2005, a soft-pulse-added-mixing (SPAM) concept was introduced by Gan and Amoureux to enhance the S/N ratio of MQMAS and STMAS experiments. Despite their robustness and simplicity, SPAM approaches have not yet been widely applied. Here, we further exploit SPAM concepts for sensitivity enhancement upon acquisition of two-dimensional MQMAS and STMAS spectra and also establish a general procedure upon implementation of SPAM-MQMAS and SPAM-STMAS NMR. Its effectiveness and ease in experimental setup are demonstrated using simulations and experiments performed on I ​= ​3/2 (23Na, 87Rb), 5/2 (27Al, 85Rb) and 9/2 (93Nb) nuclei with a variety of quadrupolar coupling constants (CQ). Compared to the conventional z-filter methods, sensitivity enhancements in between 2 and 4 are achievable with SPAM. We recommend to use SPAM with a ratio of 4:1 for the number of echoes and antiechoes to safely maximize the sensitivity and resolution simultaneously. In addition, a comparison of the experimental approaches is made in the context of SPAM-MQMAS and SPAM-STMAS NMR with respect to repetition delay and spinning frequency, aiming to discuss the precautions upon making a judicious choice of high-resolution NMR methods of half-integer quadrupolar nuclei.

The selection of correct coherence transfer pathways is an essential component of an NMR pulse sequence. This article describes a new method based on the use of web tools (eXtensible Markup Language and eXtensible Stylesheet Language Transformation) to generate a cogwheel phase cycle for selecting coherence transfer pathways. We illustrate this method with the three-pulse phase-modulated shifted-echo or split-t(1) MQMAS sequences for triple-quantum spin-3/2 systems. After generalization to the different half-integer quadrupole spins, we use the SIMPSON program to confirm our results. Finally, we apply our method to the case of the z-filter 3QMAS sequence for I=3/2 systems.

Ti x SiBEA zeolites (x = 1.5, 3.2 and 5.8 Ti wt%) are prepared by a two-step postsynthesis method involving (1) dealumination of TEABEA zeolite by nitric acid leading to nests of SiO–H groups in vacant T-atom sites and (2) incorporation of Ti into SiBEA zeolite by reacting TiCl4 vapor with those silanol groups. The incorporation of Ti into the SiBEA framework is evidenced by XRD, 29Si MAS NMR, 1H–29Si CP MAS NMR and 1H MAS NMR. DR UV–vis and XPS investigations show that, for low Ti content, mainly framework tetrahedral Ti(IV) ions are present in Ti x SiBEA zeolites. On the basis of XPS data, the quantification of framework tetrahedral Ti(IV) and framework and/or extra-framework octahedral Ti(IV) ions is followed as a function of Ti content.

The method (Dzwigaj, S., et al. Chem. Commun. 1998,87) proposed earlier to incorporate V(V) ions into the BEA zeolite framework at the solid-liquid interface from V precursors in aqueous solution has been successfully extended to the solid-gas interface and titanium, with TiCl4 vapor as the precursor. The use of TiCl4 vapor has the advantage to restrict the speciation of titanium to this single species and to lead to a significant amount of Ti (similar to 5 Ti wt %) determined by chemical analysis. The incorporation of Ti into the SiBEA zeolite framework is evidenced by XRD. The reaction of TiCl4 vapor with H-bonded and terminal SiO-H groups of vacant T-atom sites is monitored by FTIR, Si-29 MAS NMR, H-1-Si-29 CP MAS NMR and H-1 MAS NMR. The presence of tetrahedral Ti(IV) as the main titanium species is evidenced by diffuse reflectance UV-vis. A possible pathway for the formation of framework tetrahedral Ti(IV) in TiSiBEA is proposed.

The dealumination of BEA zeolite by treatment with concentrated nitric acid is evidenced by X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. Two-dimensional Al-27 3Q and 5Q magic-angle-spinning (MAS) NMR allow the detection of two kinds of tetrahedral Al atoms whose relative amounts depend on the Si/Al ratio and which correspond to two specific T-sites. Si-29 MAS NMR and H-1 MAS NMR measurements confirm these results. 29Si MAS NMR spectra evidence two resonances at around -114 and -111 ppm ascribed to Si sites of the Si(OSi)(4) environment of two different crystallographic sites. Moreover, the presence of Si atoms associated with hydroxyl groups is confirmed by a resonance at -102 ppm when H-1-Si-29 CP is applied. The Bronsted and Lewis acidic sites in dealuminated BEA zeolites are evidenced by FTIR spectra of adsorbed pyridine which show two kinds of bridging hydroxyl groups (Si-O(H)-Al) of different acid strength. V-51 MAS NMR confirms the incorporation of vanadium atoms into vacant T-atom sites of a fully dealuminated SiBEA zeolite leading to two kinds of tetrahedral V(V) sites (delta(iso) = - 708 and - 766 ppm), with a V=O double bond and linked by V-OSi bonds to the framework. The two types of tetrahedral V(V) sites are in line with the two kinds of tetrahedral Al sites initially present in the zeolite. Moreover, the two bands at 3620 and 3645 cm(-1) suggest that VSiBEA also contains V(V) sites with V(V)O-H groups, which exhibit Bronsted acidic character as shown by FTIR of adsorbed pyridine. Possible ways for the formation of tetrahedral V(V) in the BEA structure are proposed.

Since the discovery of the MQMAS method applied to quadrupolar nuclei with half-integer spin by Frydman and coworkers, this method has been considerably developed. Recently, Malicki and coworkers combined the multiplex phase cycling approach with the new SPAM method. This multiplex SPAM MQMAS sequence increases the signal-to-noise ratio by about a 2.5 factor. Additionally, this sequence can simultaneously record 3Q and 5QMAS spectra with the same acquisition. However, it is not easy to obtain experimentally, at the same time, a good signal-to-noise ratio in the two spectra. We propose a procedure for optimizing the pulse durations and finding a good compromise to record the two MQMAS spectra without peak aliasing in the F1 dimension. For this, we simulate the echo and the anti-echo amplitudes of a spin I with increasing pulse durations in a powder rotating at the magic angle, using Mathematica and SIMPSON. We apply this method to obtain the 3Q and 5QMAS spectra of Al-27 in TEABEA-11 zeolite. The latter spectrum shows two tetrahedral sites for the aluminium atoms.

Nuclei are characterized by an atomic number Z, a mass number A, and a nuclear spin I. The value of I depends on those of A and Z (Table 1). Nuclei with spin I > 2 are multiple energy level systems and are called quadrupolar nuclei. They represent more than 70% of those in the Periodic Table. However, they are not as frequently investigated in NMR as other elements, because of their quadrupole moments Q, which interact with the electric field gradient (EFG) generated by their surroundings. This coupling, called the quadrupolar interaction and denoted by HQ, may be much stronger than the amplitude of the rf excitation pulse. As a result, it affects the line intensity and alters the lineshape. These effects make the interpretation of spectra more difficult. Usually, only the first two expansion terms of HQ are considered: the first-order, (H [1] Q ), and second-order, (H [2] Q ), quadrupolar interactions, in the vocabulary of standard perturbation theory. H [1] Q splits the spectrum of a half-integer quadrupole spin system in a single crystal into 2I − 1 satellite lines, but the central line remains at the Larmor frequency ω0. The additional effect of H [2] Q is to shift further all the lines, including the central line. When the sample is in powder form, as it usually is, it is mainly the central line that is observed. Moreover, its lineshape becomes nonsymmetrical when H [2] Q is large. In favorable cases, the powder pattern of the satellite spinning sidebands is detected using the popular MAS technique (see Magic Angle Spinning and Rotating Solids). The powder pattern of the central line is characterized by three parameters: the quadrupolar coupling constant χ = e2qQ/h̄, which is the product of a nuclear property (eQ) and a crystal property (eq), the asymmetry parameter η and the center of gravity of the experimental line, δ CG (in ppm). χ is a measure of the strength of the quadrupolar interaction and η a measure of the deviation of the EFG from axial symmetry. The true chemical shift δCS of the central line is related to these three parameters:1,2

Mesoporous aluminas of controlled pore sizes were synthesized by multiple grafting of Al isopropoxide in organic solvents on mesoporous silica SBA-15. These materials were characterized by N2 physisorption, TEM, XRD, 27Al NMR and their surface chemical properties were probed by DRIFT, cumene cracking and MoO3 thermal spreading. The results show that the chemical nature of the Al-grafted materials varies continuously with the number of grafting from pure silica to pure alumina. Typically, after three graftings, this original method of synthesis allows one to prepare ordered mesoporous aluminas with specific surface areas above 300m2g−1 and a narrow pore size distribution centered on ca. 60Å. In addition to the characterizations, different models were developed to understand the evolution of the specific surface area and to discard a possible pore blocking.

The density matrix of a spin I = 7/2, excited by a radiofrequency pulse, is calculated in taking into account the first order quadrupolar interaction during the excitation. Therefore, the results are valid for any ratio of the quadrupolar coupling omega(Q) to the pulse amplitude omega(RF). The behaviour of the central line intensity versus the pulse length is discussed both in time and frequency domains. The quadrupolar coupling constant e(2)qQ/h = 8.24 MHz of the Co-59(III) nucleus in a polycrystalline sample of Na-3[Co(NO2)(6)] is determined using this one-dimensional nutation method, and the lineshape reveals mainly the presence of chemical shift anisotropy with axial symmetry.