Homonuclear decoupled INADEQUATE NMR methods with improved sensitivity and resolution in solid-state NMR.

The two-dimensional (2D) refocused INADEQUATE NMR experiment, which correlates double-quantum (DQ) and single-quantum (SQ) coherences, is widely used to probe the chemical connectivities in solids. Nevertheless, the multiplets along the F dimension reduce the resolution and sensitivity of this experiment. The Composite-Refocusing (CR) technique with two excitation pulses has been proposed to suppress these multiplets in 2D INADEQUATE spectra of liquids.

Photocatalytic dihydroxylation of light olefins to glycols by water.

Aliphatic diols such as ethylene and propylene glycol are the key products in the chemical industry for manufacturing polymers. The synthesis of these molecules usually implies sequential processes, including epoxidation of olefins using hydrogen peroxide or oxygen with subsequent hydrolysis to glycols. Direct hydroxylation of olefins by cheap and green oxidants is an economically attractive and environmentally friendly route for the synthesis of diols.

Liquid metals for boosting stability of zeolite catalysts in the conversion of methanol to hydrocarbons.

Methanol-to-hydrocarbons (MTH) process has been considered one of the most practical approaches for producing value-added products from methanol. However, the commonly used zeolite catalysts suffer from rapid deactivation due to coke deposition and require regular regeneration treatments. We demonstrate that low-melting-point metals, such as Ga, can effectively promote more stable methanol conversion in the MTH process by slowing coke deposition and facilitating the desorption of carbonaceous species from the zeolite.

Direct Identification of Zeolite Beta Polymorphs by Solid-State Si Nuclear Magnetic Resonance Spectroscopy.

Stacking disorder and polymorphism in zeolite and zeolite-like materials hinder their structural characterization. In this work, we propose an advanced approach based on applying "pure shift" solid-state Si nuclear magnetic resonance (NMR) spectroscopy for the structural investigation of zeolitic materials containing intergrown polymorphs. The approach developed in the case study of zeolite beta allows for the resolution of 21 Si signals, attributing them to non-equivalent T sites in polymorphs A, B, and C, reconstruction of individual Si magic angle spinning NMR spectra for each polymorph, and determination of the polymorph composition with higher accuracy than X-ray diffraction.

Variations in the chemical structure and Carbon-13 natural abundance in water-stable macro- and microaggregates in Haplic Chernozem under the contrasting land use variants.

Water-stable macro- (WSA) and free microaggregates (WSA) were isolated from the 2-1 mm air-dry macroaggregates from the surface horizons of Haplic Chernozem in contrasting variants of land use: the steppe and the bare fallow. The C NMR data and the C natural abundance of the Occluded organic matter (OM) (LF) and Clay within WSAs in the steppe obviously indicate a lower degree of microbiological processing of OM within WSA as compared with WSA. This is reflected in lower degrees of decomposition (DI) and aromaticity (ARI) of OM and the C/N ratio, as well as lower C enrichment.

Evaluation of Zeolite Acidity by P MAS NMR Spectroscopy of Adsorbed Phosphine Oxides: Quantitative or Not?

P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy of adsorbed alkyl-substituted phosphine oxides has witnessed tremendous progress during the last years and has become one of the most informative and sensitive methods of zeolite acidity investigation. However, quantitative evaluation of the number of sites is still a challenge. This study clarifies the main origin of errors occurring during NMR experiments, introduces the appropriate standards (both internal and external), and determines the relaxation parameters and the conditions for the acquisition and integration of spectra.

Relation between Morphology and Porous Structure of SAPO-11 Molecular Sieves and Chemical and Phase Composition of Silicoaluminophosphate Gels.

The formation of silicoaluminophosphate gels using boehmite, Al isopropoxide, and di-n-propylamine as a template of silicoaluminophosphate gels as well as their subsequent crystallization into SAPO-11 molecular sieves was studied in detail using X-ray fluorescence spectroscopy (XRF), powder X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N adsorption-desorption methods. The effect of the chemical and phase composition of silicoaluminophosphate gels on the physicochemical properties of SAPO-11 molecular sieves was shown. The secondary structural units that the AEL lattice is composed of were found to be formed at the initial stage of preparation involving aluminum isopropoxide.

Application of Multinuclear MAS NMR for the in situ Monitoring of Hydrothermal Synthesis of Zeolites.

In situ MAS NMR studies on the monitoring of hydrothermal synthesis of zeolites are reviewed. The first part of the review contains information on the experimental techniques used for the in situ NMR studies in static and MAS conditions. In the second part, the main capabilities of the in situ H, B, C, N, F, Na, Al, Si and P MAS NMR for the elucidation of the mechanism of hydrothermal synthesis of zeolites are examined and the data on NMR lines identification are summarized.

Features of the chemical structure of different organic matter pools in Haplic Chernozem of the Streletskaya steppe: C MAS NMR study.

The aim of the current research was to study structural features of four organic matter (OM) pools isolated by the modified method of granulo-densimetric fractionation from two Сhernozems. We purposed to relate these features to the OM allocation and the transformation processes. The pools included: 1) free light fraction located in an inter-aggregate space, 2) light fraction occluded inside the microaggregates, 3) OM bound with clay particles, and 4) OM bound with a residual heavy fraction left after light fractions and clay separation.

Ni-Based Nanoparticles on Mesoporous Silica Supports for Single-Stage Arsenic and Chlorine Removal during Diesel Fraction Hydrotreating.

As- and Cl-containing impurities are highly detrimental to sulfided catalysts in hydrotreating processes. To prevent the irreversible loss of activity of the main sulfide catalysts by As and Cl contaminants, a protective double-layered guard bed catalyst is applied. Two types of mesoporous silica supports (SBA-15 and MCF) were used to obtain sorption-catalytic materials.

Direct Observation of Tin in Different T-Sites of Sn-BEA by One- and Two-Dimensional Sn MAS NMR Spectroscopy.

The direct and quantitative identification of active sites is crucial for the development of zeolite catalysts and their implementation in industry. Herein we report on the application of one-dimensional Sn direct polarization (DP) and rotational echo double-resonance (REDOR) and two-dimensional Sn magic-angle tuning (MAT) NMR spectroscopy for the identification of different Sn sites in fully dehydrated Sn-BEA zeolite. It is demonstrated that Sn magic-angle spinning (MAS) NMR techniques, modified by Carr-Purcell-Meiboom-Gill (CPMG) echo-train acquisition allow to resolve three groups of NMR signals, which can be attributed to three groups of nonequivalent T-sites based on the existing theoretical predictions: (I) T9, T4, and T3; (II) T2, T1, and T8; and (III) T7, T5, and T6.

Time-Resolved In Situ MAS NMR Monitoring of the Nucleation and Growth of Zeolite BEA Catalysts under Hydrothermal Conditions.

Time-resolved C, Na, Al, and Si MAS NMR has been applied in situ for monitoring the hydrothermal synthesis of zeolite BEA. Isotopic labelling with Si and C isotopes has been used to follow the fate of siliceous species and structure directing agent (( CH -CH ) NOH). Two mechanistic pathways, namely solution-mediated and solid-solid hydrogel rearrangement have been distinguished for two synthesis procedures studied.

Application of (119)Sn CPMG MAS NMR for Fast Characterization of Sn Sites in Zeolites with Natural (119)Sn Isotope Abundance.

(119)Sn CPMG MAS NMR is demonstrated to be a fast and efficient method for characterization of Sn-sites in Sn-containing zeolites. Tuning of the CPMG echo-train sequence decreases the experimental time by a factor of 5-40 in the case of as-synthesized and hydrated Sn-BEA samples and by 3 orders of magnitude in the case of dehydrated Sn-BEA samples as compared to conventional methods. In the latter case, the reconstruction of the quantitative spectrum without the loss of sensitivity is shown to be possible.

Effect of soil properties on pure and formulated mesotrione adsorption onto vertisol (Limagne plane, Puy-de-Dôme, France).

The fate of ionisable pesticides in the environment is complex as it is importantly related to many soil properties: pH, mineralogy, organic matter content and other soil characteristics. The adsorption of a weak acid herbicide, mesotrione, was studied in detail on whole and peroxide-treated vertisol topsoil and also on its granulometric fractions (clay, silt, sand) to evaluate the role of mineralogy and different organic matter pools. The soil studied is alkaline silty loam with smectite as the main clay mineral.

Catalysis by coke deposits: synthesis of isoprene over solid catalysts.

A help rather than a hindrance: Carbonaceous deposits have been found to play a key role in the selective synthesis of isoprene from formaldehyde and isobutene over solid catalysts. They accumulate on the catalyst surface during the induction period and promote the interaction of the substrates at the steady state. The proposed mechanism shows the way forward for the design of efficient solid catalysts for the synthesis of isoprene.