MAS Nuclear Magnetic Resonance Research Articles

High-temperature synthesis of stable ordered mesoporous silica materials using mesoporous carbon as a hard template

Replicated mesoporous silica materials from CMK-3 (denoted as RSC-3-X, X stands for synthesis temperature) have been successfully synthesized in acidic media at high temperatures (160–240 °C) and subsequently characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen sorption isotherms, and 29Si nuclear magnetic resonance (NMR) spectroscopy. XRD patterns and nitrogen sorption isotherms exhibit the highly hydrothermal stable mesostructure of RSC-3 samples. Transmission electron microscopy images of RSC-3-220 show ordered hexagonal arrays of mesopores with 1D channels and further confirm the 2D hexagonal ( p6 mm) mesostructure of RSC-3-220. 29Si MAS NMR spectra indicate that as-synthesized RSC-3 samples are primarily made up of fully condensed Q 4 silica units ( δ = −112 ppm) with a small contribution from incompletely cross-linked Q 3 ( δ = −102 ppm) as deduced from the high Q 4/Q 3 ratio of 5.5–9.5, implying the fully condensed walls of RSC-3. Such unique structural features should be attributed directly to the high-temperature synthesis, which could be responsible for the observed highly hydrothermal stability of RSC-3.

Molecular Insight into the Electrostatic Membrane Surface Potential by14N/31P MAS NMR Spectroscopy: Nociceptin−Lipid Association

Exploiting naturally abundant (14)N and (31)P nuclei by high-resolution MAS NMR (magic angle spinning nuclear magnetic resonance) provides a molecular view of the electrostatic potential present at the surface of biological model membranes, the electrostatic charge distribution across the membrane interface, and changes that occur upon peptide association. The spectral resolution in (31)P and (14)N MAS NMR spectra is sufficient to probe directly the negatively charged phosphate and positively charged choline segment of the electrostatic P(-)-O-CH(2)-CH(2)-N(+)(CH(3))(3) headgroup dipole of zwitterionic DMPC (dimyristoylphosphatidylcholine) in mixed-lipid systems. The isotropic shifts report on the size of the potential existing at the phosphate and ammonium group within the lipid headgroup while the chemical shielding anisotropy ((31)P) and anisotropic quadrupolar interaction ((14)N) characterize changes in headgroup orientation in response to surface potential. The (31)P/(14)N isotropic chemical shifts for DMPC show opposing systematic changes in response to changing membrane potential, reflecting the size of the electrostatic potential at opposing ends of the P(-)-N(+) dipole. The orientational response of the DMPC lipid headgroup to electrostatic surface variations is visible in the anisotropic features of (14)N and (31)P NMR spectra. These features are analyzed in terms of a modified "molecular voltmeter" model, with changes in dynamic averaging reflecting the tilt of the C(beta)-N(+)(CH)(3) choline and PO(4)(-) segment. These properties have been exploited to characterize the changes in surface potential upon the binding of nociceptin to negatively charged membranes, a process assumed to proceed its agonistic binding to its opoid G-protein coupled receptor.

Local Structure of Amorphous (PbO)x[(B2O3)1-z(Al2O3)z]y(SiO2)y Dielectric Materials by Multinuclear Solid State NMR

Structural speciation of glasses in the systems PbO−B2O3−SiO2, PbO−B2O3−Al2O3−SiO2, and PbO−Al2O3−SiO2 were studied using solid state 29Si, 27Al, 11B, and 207Pb nuclear magnetic resonance (NMR) and Raman spectroscopy. Application of these methods provided insight into the role of Al2O3 incorporation in the lead borosilicate glass networks. The general composition range studied was (PbO)x[(B2O3)1-z(Al2O3)z]y(SiO2)y where x = 0.35, 0.5, and 0.65, y = (1 − x)/2 and z = 0.0, 0.5, and 1.0. Additional insight was obtained via 27Al 2D-3QMAS experiments. The 207Pb spin−echo mapping spectra showed a transition from ionic (Pb2+) to covalently bound lead species with increased PbO contents in the borosilicate glasses. The addition of aluminum to the glass network further enhanced the lead species transition, resulting in a higher relative amount of covalent lead bonding in the high PbO content alumino-borosilicate glass. The number of BO4 units present in the 11B MAS NMR decreased with increasing PbO contents for both the borosilicate and the alumino-borosilicate glass systems, with the addition of aluminum further promoting the BO3 species. A deshielding of the 11B chemical shifts and the 27Al chemical shifts with increased lead contents (independent of changes in the quadrupolar coupling) was also observed for both glass systems and was attributed to an increasingly homogeneous glass structure. The 29Si spectra of the borosilicate and alumino-borosilicate glasses showed a downfield shift with increased PbO concentrations representing incorporation of Pb into the silicate and aluminosilicate networks. The Raman spectra were characterized by increased intensities of Si−O−Pb peaks and decreased intensities of Q3 peaks with increased PbO contents and showed no evidence of BO3 or BO4 ring species. Both the NMR and the Raman data point toward systems where lead is increasingly incorporated into the B2O3−SiO2 and the B2O3−SiO2−Al2O3 networks at high PbO concentrations, with the addition of Al2O3 enhancing the trend.

Dissolution mechanisms of water in depolymerized silicate melts: Constraints from 1H and 29Si NMR spectroscopy and ab initio calculations

Dissolution of water in magmas significantly affects phase relations and physical properties. To shed new light on the this issue, we have applied 1H and 29Si nuclear magnetic resonance (NMR) spectroscopic techniques to hydrous silicate glasses (quenched melts) in the CaO-MgO-SiO 2 (CMS), Na 2O-SiO 2, Na 2O-CaO-SiO 2 and Li 2O-SiO 2 systems. We have also carried out ab initio molecular orbital calculations on representative clusters to gain insight into the experimental results. The most prominent result is the identification of a major peak at ∼1.1 to 1.7 ppm in the 1H MAS NMR spectra for all the hydrous CMS glasses. On the basis of experimental NMR data for crystalline phases and ab initio calculation results, this peak can be unambiguously attributed to (Ca,Mg)OH groups. Such OH groups, like free oxygens, are only linked to metal cations, but not part of the silicate network, and are thus referred to as free hydroxyls in the paper. This represents the first direct evidence for a substantial proportion (∼13∼29%) of the dissolved water as free hydroxyl groups in quenched hydrous silicate melts. We have found that free hydroxyls are favored by (1) more depolymerized melts and (2) network-modifying cations of higher field strength (Z/R 2: Z: charge, R: cation-oxygen bond length) in the order Mg > Ca > Na. Their formation is expected to cause an increase in the melt polymerization, contrary to the effect of SiOH formation. The 29Si MAS NMR results are consistent with such an interpretation. This water dissolution mechanism could be particularly important for ultramafic and mafic magmas. The 1H MAS NMR spectra for glasses of all the studied compositions contain peaks in the 4 to 17 ppm region, attributable to SiOH of a range of strength of hydrogen bonding and molecular H 2O. The relative population of SiOH with strong hydrogen bonding grows with decreasing field strength of the network-modifying cations. Ab initio calculations confirmed that this trend largely reflects hydrogen bonding with nonbridging oxygens.

1H MAS NMR (Magic-Angle Spinning Nuclear Magnetic Resonance) Techniques for the Quantitative Determination of Hydrogen Types in Solid Catalysts and Supports

Distinct hydrogen species are present in important inorganic solids such as zeolites, silicoaluminophosphates (SAPOs), mesoporous materials, amorphous silicas, and aluminas. These H species include hydrogens associated with acidic sites such as Al(OH)Si, non-framework aluminum sites, silanols, and surface functionalities. Direct and quantitative methodology to identify, measure, and monitor these hydrogen species are key to monitoring catalyst activity, optimizing synthesis conditions, tracking post-synthesis structural modifications, and in the preparation of novel catalytic materials. Many workers have developed several techniques to address these issues, including 1H MAS NMR (magic-angle spinning nuclear magnetic resonance). 1H MAS NMR offers many potential advantages over other techniques, but care is needed in recognizing experimental limitations and developing sample handling and NMR methodology to obtain quantitatively reliable data. A simplified approach is described that permits vacuum dehydration of multiple samples simultaneously and directly in the MAS rotor without the need for epoxy, flame sealing, or extensive glovebox use. We have found that careful optimization of important NMR conditions, such as magnetic field homogeneity and magic angle setting are necessary to acquire quantitative, high-resolution spectra that accurately measure the concentrations of the different hydrogen species present. Details of this 1H MAS NMR methodology with representative applications to zeolites, SAPOs, M41S, and silicas as a function of synthesis conditions and post-synthesis treatments (i.e., steaming, thermal dehydroxylation, and functionalization) are presented.

Water speciation and Sr isotopic exchange during water–melt interaction: a combined NMR–TIMS study on the Cretaio Tephra (Ischia Island, south Italy)

In order to improve the microscopic understanding of the water–magma interaction process during explosive volcanism, volcanic glasses representative of deposits with sedimentological characteristics suggesting different water/melt ratios were studied by a combination of the nuclear magnetic resonance (NMR) and TIMS methods. The glasses were separated from pumices of two surge layers and one fallout bed of the Cretaio Tephra (Ischia Island, Italy), which is the product of an explosive eruption that occurred at Ischia in the second century BC. The 29Si CP–MAS NMR experiments indicate the occurrence of 1H– 29Si dipolar couplings in glasses from the phreatomagmatic activity, suggesting the presence of hydrogen atoms in proximity of silicon atoms. This feature is not detected in the glass from the deposit of the magmatic explosion. 1H MAS NMR spectra reveal different peaks attributed to different hydrous species characterized by different motional properties. These include ‘rigid’ H 2O groups isolated in the glass structure, more mobile water species and possibly structural hydroxyl groups. 1H MAS NMR spectra recorded after deuteration experiments of the glass at a temperature up to 300°C revealed that the exchange reactions of the D 2O vapor with hydrogen were limited to the most mobile water species, possibly on vesicle surfaces or in channels. The hydrogen concentration linearly correlates with the 87Sr/ 86Sr isotope ratio in glasses, suggesting isotopic tracer exchanges between the Sr dissolved in the water vapor and the Sr in the silicon–oxygen network during hydration. It is proposed that the uprising melt interacted with a hydrothermal system of seawater-derived fluids, characterized by relatively high Sr isotopic composition.

The use of solid state nuclear magnetic resonance (NMR) to study the effect of composition on the properties of equilibrium fluid cracking catalysts (FCCs)

Solid state nuclear magnetic resonance (NMR) spectroscopy together with microactivity testing have been used to characterize the changes that occur in a fluid cracking catalyst (FCC) during gas oil cracking in a refinery fluid catalytic cracking unit (FCCU). The 29 Si NMR spectra of fresh FCCs show the well known five peaks pattern attributed to the presence of HY-type crystals. However, after aging, equilibrium FCCs are generated in which the 29 Si NMR spectrum of the zeolitic component is reduced to one main dominant resonance near −107 ppm representative of T[4Si,0Al] sites. Thus, irrespective of composition, extensive dealumination of the cracking component in FCCs occurs during recirculation in a FCCU yielding 29 Si NMR spectra in which the presence of framework Al is no longer visible. Similar conclusions have been obtained from the corresponding 27 Al MAS NMR spectra showing that the dealuminated faujasite structure in equilibrium FCCs contains only extra-framework Al(IV), Al(V), and Al(VI) species. In the presence of tin, vanadium effects on the coordination of Al and Si in equilibrium FCCs, could not be observed by 29 Si or 27 Al NMR spectroscopy.

Two Types of Alzheimer's β-Amyloid (1–40) Peptide Membrane Interactions: Aggregation Preventing Transmembrane Anchoring Versus Accelerated Surface Fibril Formation

The 39–42 amino acid long, amphipathic amyloid-β peptide (Aβ) is one of the key components involved in Alzheimer's disease (AD). In the neuropathology of AD, Aβ presumably exerts its neurotoxic action via interactions with neuronal membranes. In our studies a combination of 31P MAS NMR (magic angle spinning nuclear magnetic resonance) and CD (circular dichroism) spectroscopy suggest fundamental differences in the functional organization of supramolecular Aβ1–40 membrane assemblies for two different scenarios with potential implication in AD: Aβ peptide can either be firmly anchored in a membrane upon proteolytic cleavage, thereby being prevented against release and aggregation, or it can have fundamentally adverse effects when bound to membrane surfaces by undergoing accelerated aggregation, causing neuronal apoptotic cell death. Acidic lipids can prevent release of membrane inserted Aβ1–40 by stabilizing its hydrophobic transmembrane C-terminal part (residue 29–40) in an α-helical conformation via an electrostatic anchor between its basic Lys28 residue and the negatively charged membrane interface. However, if Aβ1–40 is released as a soluble monomer, charged membranes act as two-dimensional aggregation-templates where an increasing amount of charged lipids (possible pathological degradation products) causes a dramatic accumulation of surface-associated Aβ1–40 peptide followed by accelerated aggregation into toxic structures. These results suggest that two different molecular mechanisms of peptide–membrane assemblies are involved in Aβ′s pathophysiology with the finely balanced type of Aβ–lipid interactions against release of Aβ from neuronal membranes being overcompensated by an Aβ–membrane assembly which causes toxic β-structured aggregates in AD. Therefore, pathological interactions of Aβ peptide with neuronal membranes might not only depend on the oligomerization state of the peptide, but also the type and nature of the supramolecular Aβ–membrane assemblies inherited from Aβ′s origin.

Synthesis of dealuminated zeolites NaY and MOR and characterization by diverse methodologies: 27Al and 29Si MAS NMR, XRD, and temperature dependent 129Xe NMR

Zeolites NaY and mordenite have been dealuminated by SiCl 4 and steaming methods and carefully characterized during and after the various synthetic stages by 27Al and 29Si magic angle spinning nuclear magnetic resonance (NMR) and X-ray diffraction (XRD) to ensure sample quality. 129Xe NMR spectra for xenon adsorbed in NaX, siliceous Y, mordenite, and dealuminated mordenite have been obtained for very low xenon loadings and as a function of temperature. Data obtained for faujasites indicate that 129Xe NMR chemical shifts are very sensitive to the Si/Al ratio reflecting the presence or absence of strong adsorption sites. 129Xe NMR chemical shift data for the mordenite samples show that Xe dwells preferentially in the side pockets which do not seem to be affected by the dealumination process. In addition, the 129Xe NMR data clearly reveal information not available from 29Si and 27Al NMR or XRD regarding structural integrity of the zeolites. The findings presented here point to the need for characterization of siliceous zeolites by several techniques before conclusions regarding zeolite structural integrity can be drawn.

Structural and lithium intercalation studies of Mn (0.5− x) Ca xTi 2(PO 4) 3 phases (0≤ x≤0.50)

Materials from the Mn (0.5− x) Ca x Ti 2(PO 4) 3 (0≤ x≤0.50) solid solution were obtained by solid-state reaction in air at 1000 °C. Selected compositions were investigated by powder X-ray diffraction analysis, 31P nuclear magnetic resonance (NMR) spectroscopy and electrochemical lithium intercalation. The structure of all samples determined by Rietveld analysis is of the Nasicon type with the R3̄ space group. Mn 2+/Ca 2+ ions occupy only the M1 sites in the Ti 2(PO 4) 3 framework. The divalent cations are ordered in one of two M1 sites, except for the Mn 0.50Ti 2(PO 4) 3 phase, where a small departure from the ideal order is observed by XRD and 31P MAS NMR. The electrochemical behaviour of Mn 0.50Ti 2(PO 4) 3 and Mn (0.5− x) Ca x Ti 2(PO 4) 3 phases was characterised in Li cells. Two Li ions can be inserted without altering the Ti 2(PO 4) 3 framework. In the 0≤ y≤2 range, the OCV curves of Li//Li y Mn 0.50Ti 2(PO 4) 3 cells show two main potential plateaus at 2.90 and 2.50–2.30 V. Comparison between the OCV curves of Li//Li (1+ y) Ti 2(PO 4) 3 and Li//Li y Mn 0.50Ti 2(PO 4) 3 shows that the intercalation occurs first in the unoccupied M1 site of Mn 0.50Ti 2(PO 4) 3 at 2.90 V and then, for compositions y>0.50, at the M2 site (2.50–2.30 V voltage range). The effect of calcium substitution in Mn 0.50Ti 2(PO 4) 3 on the lithium intercalation is also discussed from a structural and kinetic viewpoint. In all systems, the lithium intercalation is associated with a redistribution of the divalent cation over all M1 sites. In the case of Mn 0.50Ti 2(PO 4) 3, the stability of Mn 2+ either in an octahedral or tetrahedral environment facilitates cationic migration.

Dependence of Ionic Conductivity on Composition of Fast Ionic Conductors Li1+xTi2-xAlx(PO4)3, 0 ≤ x ≤ 0.7. A Parallel NMR and Electric Impedance Study

Materials with nominal compositions Li1+xTi2-xAlx(PO4)3, 0 ≤ x ≤ 0.7, have been prepared and studied with X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and electrical impedance techniques. Substitution of Ti4+ by Al3+ reduces the unit cell dimensions of the NASICON framework but enhances the grain interior conductivity. The overall conductivity is dominated by the grain boundary composition. Detection of new broad peaks in the 31P and 27Al MAS NMR spectra supports the formation of an amorphous Li-conducting phase that accounts for the increase observed in the overall conductivity. In samples with x > 0.5, crystallization of Li4P2O7 as a segregated phase is accompanied by the appearance of a new electrical response. In these samples, a decrease in overall conductivity, associated with a modification of the amorphous phase, is also observed.

Synthesis and characterization of manganese-modified MCM-41

Manganese-modified mesoporous MCM-41 molecular sieves were synthesized at the absence of alkaline metal ions under mild alkaline condition using cetylpyridinium bromide surfactant as a template, and characterized with X-ray diffraction, N 2 adsorption, transmission electron microscopy, electron spin resonance (ESR), and nuclear magnetic resonance (NMR) spectroscopies. The synthesized MnMCM-41 has a high pore volume of 1.30 cm 3 g −1 with a corresponding surface area of 1510 m 2 g −1. The ESR and 29 Si MAS NMR spectra revealed the presence of framework manganese ions in either the as-synthesized or calcined forms.

A 13C and 15N Solid State NMR Study of the Reactions of Acetone Oxime Adsorbed on FeZSM-5

The reactions of acetone oxime, a proposed reaction intermediate for the SCR (Selective Catalytic Reduction) of NO with propane on FeZSM-5, have been studied with 13C and 15N solid state MAS NMR (magic angle spinning nuclear magnetic resonance). FeZSM-5 with three different loading levels was prepared by the sublimation method. The thermal reactions of acetone [2-13C] oxime adsorbed on FeZSM-5 samples with different iron loadings were monitored by 13C MAS NMR by heating to the desired temperature and then cooling to room temperature for data acquisition. For the sample with the lowest iron loading (Fe/Al = 0.11), acetic acid and N-methyl-2-propanamine were formed by the decomposition of acetone oxime. For the samples with the higher iron loadings (Fe/Al = 0.69 and 0.91), acetone, N,N′-methyl-2,2-propanediamine, and N-methyl-2-propanimine were formed by the decomposition of acetone oxime. 15N MAS NMR was used to investigate reactions of 15NO and acetone oxime on the FeZSM-5 samples. The formation of gas phase N2 and N2O was observed.

Gel‐to‐Ceramic Conversion during Hydroxyapatite Synthesis

Conversion of hydroxyapatite (HA, Ca10(PO4)6(OH)2) synthesis from gel to ceramic using solid‐state nuclear magnetic resonance (NMR) spectroscopy and X‐ray diffraction was studied. The sol was prepared by dissolving calcium nitrate tetrahydrate and triethyl phosphate in 2‐methoxyethanol. In solid‐state 31P magic‐angle spinning nuclear magnetic resonance (MAS NMR) spectra, gel calcined at 250°, 350°, and 600°C showed a conversion from gel to glassy phosphate, then HA ceramic. Spin‐lattice relaxation experiments of samples calcined at 600°C indicated that the existence of a CaO impurity might affect OH···O=PO3 linkages in a HA unit cell and result in longer 31P spin‐lattice time.

Magnetic Susceptibility Effects on 13C MAS NMR Spectra of Carbon Materials and Graphite

13C high-resolution solid-state nuclear magnetic resonance (NMR) was employed to study carbon materials prepared through the thermal decomposition of four different organic precursors (rice hulls, endocarp of babassu coconut, peat, and PVC). For heat treatment temperatures (HTTs) above about 600°C, all materials presented 13C NMR spectra composed of a unique resonance line associated with carbon atoms in aromatic planes. With increasing HTT, a continuous broadening of this resonance and a diamagnetic shift in its central frequency were verified for all samples. The evolution of the magnitude and anisotropy of the magnetic susceptibility of the heat-treated carbon samples with HTT explains well these findings. It is shown that these results are better understood when a comparison is made with the features of the 13C NMR spectrum of polycrystalline graphite, for which the magnetic susceptibility effect is also present and is much more pronounced.

Comparative analysis of black carbon in soils

Black carbon (BC), produced by incomplete combustion of fossil fuels and vegetation, occurs ubiquitously in soils and sediments. BC exists as a continuum from partly charred material to highly graphitized soot particles, with no general agreement on clear‐cut boundaries of definition or analysis. In a comparative analysis, we measured BC forms in eight soil samples by six established methods. All methods involved removal of the non‐BC components from the sample by thermal or chemical means or a combination of both. The remaining carbon, operationally defined as BC, was quantified via mass balance, elemental composition or by exploiting benzenecarboxylic acids as molecular markers or applying 13C MAS NMR (magic angle spinning nuclear magnetic resonance) spectroscopy. BC concentrations measured for individual samples vary over 2 orders of magnitude (up to a factor of 571). One possible explanation for this wide range of results is that the individual BC methods rely on operational definitions with clear‐cut but different boundaries and developed for specific scientific questions, whereas BC represents a continuum of materials with widely contrasting physicochemical properties. Thus the methods are inherently designed to analytically determine different parts of the continuum, and it is crucial to know how measurements made by different techniques relate to each other. It is clear from this preliminary comparative analysis that a collection of BC reference materials should be established as soon as possible 1 ) to ensure long‐term intralaboratory and interlaboratory data quality and 2) to facilitate comparative analyses between different analytical techniques and scientific approaches

Firing temperature dependence of Eu diffusion in Eu-Y2O2S studied by 89Y MAS NMR

89 Y MAS NMR (magic angle spinning nuclear magnetic resonance) and powder X-ray diffraction were applied in order to elucidate the crystal growth process, Eu doping process, and Eu distribution in a red phosphor, Eu-doped Y2O2S (Eu-Y2O2S), fired at varying temperatures, as well as the correlation between such material properties and the phosphor quality. The spin–lattice relaxation time (T1) was measured for the main peak at 292 ppm due to Y atoms located far from the paramagnetic Eu and for the satellite peaks due to three types of Y1 atoms [here, Y1 is the Y atom μ-bridged by O and/or S atoms to an Eu atom, such as Y1(–O–,–S–)Eu]. The T1 values for Y1, T1(Y1), were independent of the firing temperature from 900 to 1200°C and depend on the type of μ-bridge, indicating that T1(Y1) is not influenced by crystal characteristics such as crystallite size and degree of lattice disorder, but is influenced by the interatomic distance between Y1 and the doped Eu. The T1 values of the main peak, T1(Yn), were influenced by the Eu distribution. Comparing T1(Yn) to parameters such as the chromaticity coordinates, brightness and intensity of emission, it was found that the substitution of Eu at the Y site in Y2O2S and the random distribution of Eu are accelerated with the elevation of the firing temperature from 900 to 1200°C. The amount of Eu substituted at random into the Y2O2S crystal was evaluated as the effective Eu concentration for monitoring the properties of the phosphor. The interrelation between the brightness, the line-width and T1(Yn) in 89Y NMR, the amount of effective Eu, and the crystallinity of Eu-Y2O2S was elucidated.

Sol–gel synthesis, characterization by solid state NMR and HDS activity of Mo–alumina and Mo–P–alumina based catalysts

The aim of the present study was to prepare different Mo–alumina and Mo–P–alumina catalysts by a sol–gel method. The wishes were to underline the influence of the way to introduce the different Mo and/or P elements in the architecture of the dried and calcined solids and the consequences on their catalytic properties. During the sol–gel alumina synthesis, molybdenum [precursor=(NH 4) 6Mo 7O 24·4H 2O] and phosphorus (precursor=H 3PO 4) can be introduced separately or simultaneously in 2-butanol (step 1) or in water (step 3) to obtain the final mixed oxide. For Mo–alumina, the influence of the amount of molybdenum (Mo/Al ratio=0.1, 0.2 or 0.3) has been studied, whereas for the Mo–P–Al solids, four combinations have been prepared with a fixed Mo/Al ratio at 0.2 and P/Al ratio at 0.03 and 0.2. The dried and calcined samples have been extensively characterized by 27Al, 31P MAS NMR and 27Al Multiple Quantum Magic Angle Spinning NMR (MQMAS NMR). After sulfidation, the solids have been tested in hydrodesulfurization (HDS) of thiophene. It appears that the activity of Mo–Al catalysts increases when the molybdenum amount increases and when molybdenum is dissolved in 2-butanol during the synthesis. A promotor effect of phosphorus has been observed in some cases, particularly, when the molybdenum and the phosphorus precursors are both dissolved in water. Moreover, this study has shown the importance of the step of introduction of phosphorus for the catalytic performances of the Mo–P–Al catalysts. These catalytic results are correlated with some nuclear magnetic resonance (NMR) characterizations, which evidence the formation of different aluminium phosphates.

Electronic and structural properties of reduced-charge montmorillonites

Solid state silicon ( 29 Si ) and aluminum ( 27 Al ) nuclear magnetic resonance (NMR) spectroscopies were applied to a series of reduced-charge montmorillonites (RCMs) to discern changes in electronic and structural properties that are induced by Li fixation. Room temperature 29 Si MAS NMR spectra revealed a consistent chemical shift to more negative values and increased line width of the main Q 3(0Al) Si resonance with increasing levels of Li fixation in the RCM series. A decreased line width of the octahedral Al (Al [6]) environment was observed and may be attributed to formation of a more uniform electronic environment surrounding Al [6] as charge reduction occurs. No appreciable changes in the tetrahedral Al (Al [4]) peak were observed for the series, except for line broadening. Correlations of 29 Si NMR chemical shifts with layer charge and infrared-active structural vibrations indicated that distortions in the Si–O–T bond angles (T=tetrahedral Si or Al) occurred, with the mean Si–O–T bond angle increasing, following charge reduction. These results are interpreted as evidence of a redistribution both of layer charge and an abatement of the fit between octahedral and tetrahedral sheets following Li fixation and charge reduction. Our results are consistent with the formation of pyrophyllite-like character in reduced-charge montmorillonite.

Characterization of Polyalkylvinyl Ether Phases by Solid-State and Suspended-State Nuclear Magnetic Resonance Investigations

Pure organic polyalkylvinyl ether phases were synthesized by suspension polymerization using different ratios and compositions of n-butylvinyl ether (C4VE) and n-octadecylvinyl ether (C18VE) with triethylene glycol divinyl ether or divinylbenzene as crosslinkers, respectively. These phases were investigated by means of solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance (NMR) spectroscopy and 1H high-resolution magic angle spinning (HR MAS) NMR spectroscopy in suspended-state. A comparison of these two methods showed the substantial advantages of 1H HR MAS NMR measurements. Structure elucidation was achieved using a 2D H,H-COSY NMR experiment performed under MAS conditions enabling full peak assignment of the 1H NMR spectra of these phases. The dynamic behavior of the polyalkylvinyl ether phases was determined by employing temperature-dependent measurements of spin–lattice relaxation times (T1) as well as accumulation of a 2D wide line separation NMR spectrum.