丝光沸石催化剂的固体高分辨核磁共振研究

利用²⁹Si MAS NMR及²⁷Al MAS NMR技术研究了丝光沸石催化剂制备过程中的结构变化,并利用Al的四极作用大小来区分重叠在一起的不同的Al物种.     

Y型沸石脱铝机制和铝状态的NMR研究

对Y型沸石原粉及几种不同脱铝样品进行了几种不同NMR方法的测量,确定了不同处理过程的脱铝机制和骨架内外铝状态的变化,²⁹Si MAS NMR谱给出了骨架Si、Al分布的信息,反映了不同方法处理样品其脱铝机制的差异,据此可以控制Y沸石脱铝过程获得更高的硅铝比,²⁷Al MAS NMR谱、二维章动NMR及¹H-²⁷Al CP/MAS NMR测量表明:水热处理的Y沸石中存在4种不同的铝状态。综合²⁹Si和²⁷Al MAS NMR观测,可相当程度地推断Y型沸石分子筛脱铝改性所发生的内部过程。     

Multinuclear NMR studies on the sol-gel preparation of sodium aluminophosphate glasses

Sodium aluminophosphate gels and glasses in the system NaPO₃–Al₂O₃ with P/Al ratios ranging from 9:1 to 1:1 have been synthesized by a novel sol–gel route based on the reaction of aluminum lactate with sodium polyphosphate in aqueous solution. The route from the solution to the gel and the final glass was monitored in situ by liquid and solid state NMR techniques, characterizing the influence of composition and pH on the hydrolysis, polymerization, and vitrification processes. The site distribution in the xerogels is strongly influenced by the gel-processing temperature. At temperatures near 150°C ligation with lactate groups can be nearly suppressed, resulting in maximum Al/P connectivity in the gel. Annealing the gels at temperatures near 400°C produces significant structural rearrangements, resulting in a glassy network that has close structural similarity to the glasses derived from the usual melt-cooling procedure at 1100–1450°C. This has been confirmed by extensive ²⁷Al, ³¹P and ²³Na MAS NMR as well as ²⁷Al{³¹P} and ²⁷Al {¹H} double resonance experiments. Compared to melt-cooling, the sol–gel process permits a significant extension of the glass-forming region towards higher alumina contents.     

27Al NMR study in ZrNiAl

We have studied the microscopic properties of the hexagonal ZrNiAl, a model compound for a wide family of intermetallic compounds crystallizing in this type of structure, by using ²⁷Al NMR spectroscopy. We have investigated the lineshape of static and MAS NMR spectra as a function of magnetic field strength (4.7–9.4 T) and temperature (5–300 K). Our data indicate that the ²⁷Al NMR spectra result from a combined effect of quadrupole and anisotropic shift interactions. The ²⁷Al nuclei are in an environment characterized by the quadrupole coupling constant e²qQ/h of 3.3 MHz, asymmetry parameter η_Q of 0.42, isotropic shift δ_iso of 393 ppm, shift anisotropy δ_anis = δ_zz − (δ_xx + δ_yy)/2 of 150 ppm, and asymmetry factor η_S of 0.5. They are found to be temperature independent. The spin–lattice relaxation rate measured at 7.05 T is proportional to the temperature with T₁T = 135 s K. The mechanisms responsible for observed values of δ_iso, δ_anis, T₁T, and the enhanced Korringa constant are discussed.     

The surface structure of catalysts activated with hydrogen donors as elucidated by multinuclear solid-state NMR

¹H, ²⁷Al and ³¹P MAS, and ¹³C and ²⁹Si CP/MAS NMR spectroscopies, were used to characterize catalysts of Pd supported on various solids including SiO₂, AlPO₄ and Mg₃(PO₄)₂ that were activated with the chiral hydrogen-donor limonene. The above-mentioned techniques were used to check for the formation of an organopalladium complex between Pd²⁺ atoms and the olefin bonds in the limonene molecule on the catalyst surface. The results are compared with those obtained for catalysts activated in a hydrogen stream.     

Solid-state NMR investigation on the interactions between a synthetic montmorillonite and two homopolypeptides

Interactions of two homopolypeptides (polylysine and polyglutamic acid) with a synthetic montmorillonite were studied by ¹H MAS, ¹H–²⁷Al HETCOR and ¹H–¹³C CP-MAS NMR experiments. ¹H–²⁷Al HETCOR with ¹H spin-diffusion NMR appears to be a powerful probe for the identification of the polypeptide fragments, which interact with the montmorillonite interlayer surfaces. In particular, selective interactions were observed between the polypeptide side-chains and the montmorillonite octahedral aluminum atoms. ¹H–¹³C CP-MAS NMR experiments were used to assess the dynamics of the two polypeptides through the measurement of the t_1/2 characteristic time of selected carbons. Results indicate that the local mobility of the side chains and their interaction with the montmorillonite layers depend on the nature of the adsorbed polypeptides.     

27Al and 65Cu NMR study in UCu5Al.

We have studied the microscopic properties of the tetragonal UCu₅Al Kondo compound by ²⁷Al and ^63,65Cu NMR in the paramagnetic state. NMR and susceptibility measurements performed on the powdered sample, but oriented along the applied field, showed χ>χ. Plots of K(T) against χ(T) at temperatures T≥100 K yield the transferred hyperfine fields of +5.9 kOe/μ_B for ²⁷Al nuclei, and +5.3 and −7.0 kOe/μ_B for ⁶⁵Cu nuclei in crystallographically inequivalent Cu(2) and Cu(1) sites, respectively. The Knight shift vs. susceptibility plots for T<100 K exhibit a deviation from the linear behaviour (absolute values of shifts become smaller than expected). We attribute this finding to the crystalline electric field effect in similar way as it was reported for several Ce-based compounds. The random distribution of the Al and Cu(2) atoms in the crystal lattice we consider as a reason of an unusual broadening of the NMR spectra, particularly at low temperatures.     

1D and 2D solid state NMR investigations of the framework structure of As-synthesized AlPO4-14

The framework structure of As-synthesized A1PO₄-14 has been investigated with a combination of different one-dimensional ²⁷Al and ³¹P solid state NMR techniques and ²⁷Al/³¹P double resonance methods. The results are found to be fully consistent with the assumed structural model. ²⁷Al MAS and DOR experiments at three different magnetic field strengths together with simulations show the presence of two tetrahedral sites, one pentacoordinated and one octahedral aluminum site. The ²⁷Al quadrupolar coupling constants and the ³¹P isotropic chemical shifts of the tetrahedral sites correlate well with tetrahedral shear-strain parameters and mean P-O-A1 bond angles, respectively. These correlations allow one to assign all of the NMR resonances to specific T-sites in the proposed framework structure. The assignments are then further confirmed by the application of three different two-dimensional heteronuclear correlation methods (i.e., ²⁷Al → ³¹P TEDOR, CP, and INEPT) which reveal the connectivities between AlO_x and PO₄ polyhedra. The two-dimensional INEPT experiment is applied here for the first time in the solid state.     

A Al MAS, MQMAS and off-resonance nutation NMR study of aluminium containing silica-based sol-gel materials

Aluminium containing hybrid materials were prepared via the sol-gel method using aluminium sec-butoxide complexed with ethylacetoacetate (Al(OBu^s)₂EAA or Al(OBu^s)₃/EAA mixtures). As silanes, phenyltrimethoxysilane (PhTMS) or phenyltriethoxysilane (PhTES), 3-glycidoxypropyl trimethoxysilane (Glymo) and tetraethylorthosilicate (TEOS) were used. After room temperature drying of the samples the ²⁷Al single pulse excitation (SPE) magic angle spinning (MAS) NMR shows that octahedral (5 ppm) and tetrahedral (55 ppm) coordinated aluminium species are present in the materials. The relative amount of these two species depends on the preparation method. However, the Al(IV)/Al(VI) ratio is lower than 3 (typically 2.3) in all materials, indicating the presence of a small amount of an aluminate phase. Annealing of the samples at 100, 150 and 200 °C results in the formation of an extra signal at 30 ppm (peak maximum measured at 11.7 T). Based on the resonance frequency this signal is generally assigned to a pentahedrally coordinated aluminium species. Hydration/dehydration processes of annealed samples were studied with ²⁷Al SPE MAS NMR, multiple-quantum MAS NMR (MQMAS) and off-resonance nutation NMR. Upon hydration of the annealed sample the signal intensity around 30 ppm decreases in intensity and at the same time the intensity of the signal around 55 ppm increases by the same amount (tetrahedrally coordinated aluminium). The MQMAS spectra reveal that the signal around 30 ppm is not caused by a fivefold-coordinated aluminium species but mainly by tetrahedrally coordinated aluminium species in a distorted environment, experiencing large quadrupole induced shifts and small chemical shifts due to conformational changes in the polymeric network. From the MQMAS NMR spectra it can be concluded that the linebroadening observed in the ²⁷A1 MAS NMR spectra is due to both a distribution in isotropic chemical shifts and a distribution in quadrupole coupling constants (C_qcc = e²qQ/h). Hydration of the sample results in a decrease of the average C_qcc for the tetrahedrally coordinated aluminium from 6 to 4 MHz, whereas the average C_qcc of the octahedrally coordinated aluminium is hardly influenced (4 MHz). These MQMAS results are confirmed by off-resonance nutation experiments.     

Li1+2xTi2-xMgxP3O12固溶体系统结构31P NMR研究

本文应用固体高分辨³¹P NMR技术,以P原子作为结构探针,对以LiTi2P₃O₁₂为基质的Mg掺杂固溶体系统快离子导体的结构进行了研究。并利用P原子第二配位层阳离子场强与其化学位移的关系,确定了不同化学位移³¹P NMR谱线与固溶体结构中P原子局部结构单元Q°之间的关系,解释了Mg的掺入所引起的晶体结构的变化。     

NMR study of solid C60(γ-cyclodextrin)2

A solid complex of C₆₀ with γ-cyclodextrin (γ-CyD) was examined with NMR spectroscopic methods in order to understand the dynamics of C₆₀, and the interaction between C₆₀ and γ-CyD. A ¹³C solid-state cross-polarization magic angle spinning (CP/MAS) NMR spectra shows C₆₀ resonance at 142.6 ppm. This provides the evidence of interaction between ¹³C spins in C₆₀ and ¹H spins in the γ-CyD host. Ambient temperature experiments on the ¹³C CP/MAS NMR, with varying contact time, shows that the water associated with γ-CyDs plays an important role in the nuclear relaxation processes. The dynamics of C₆₀ in γ-CyD was investigated using temperature and field-dependent ¹³C spin-lattice relaxation time measurements. The influence of water on the dynamics of C₆₀ was less significant below 250 K.     

Adsorption of Na onto γ-alumina studied by solid-state Na and Al nuclear magnetic resonance spectroscopy

The adsorption of Na⁺ on γ-alumina surfaces at four coverages of Na₂CO₃ [5, 10, 15 and 20% (w/w)] was characterized by solid-state ²³Na and ²⁷Al nuclear magnetic resonance (NMR) spectroscopy. The experimental results suggest that two distinct adsorbed species are present on the alumina surface: surface species and surface salts. At the lower coverages of Na₂CO₃ (5 and 10%), the surface species is predominant, in which the Na⁺ cations are associated with the oxygen atoms of γ-alumina. Increasing the loading level to 15% results in the appearance of a second adsorbed species that is attributed to the surface salt, Na₂CO₃, deposited on the solid surface. Further adsorption of Na₂CO₃ leads to an increase in the amount of surface salt while the amount of surface species remains unchanged. ¹H---²⁷Al Cross-polarization magic angle spinning (CP-MAS) experiments give the evidence that some Na⁺ cations in the form of surface species are coordinated with the Brönsted acid sites of γ-alumina. This may be the main driving force that improves appreciably the catalytic efficiency of an Na₂CO₃---Al₂O₃ catalyst.     

X-ray and high resolution selenium-77 solid state NMR spectroscopy as complementary probes to structural studies of organophosphorus diselenides

high resolution solid state NMR spectroscopy was employed to study structural properties of bis(diisopropoxyphosphorothioyl) diselenide 1 and bis(dineopentoxyphosphorothioyl) diselenide 2. The principal elements T_ii of effective dipolar/chemical shift tensor were calculated from spinning sideband intensities employing the WIN-MAS program. The values of anisotropy and asymmetry parameters reflect the distortion of the selenium environment. It was found that the T₃₃ component mostly contributes to changes in the isotropic chemical shifts. CP/MAS experiments were used to decide the assignment of space group by counting the number of crystallographically unique selenium centers in the unit cell. Crystals of diselenide 1 are triclinic, space group P with a=8.485(3) Å, b=8.508(1) Å, c=8.511(2) Å, =98.835(15)°, β=111.653(24)°, γ=93.524(21)°, V=559.5(3) ų, D_c=1.544(2) g/cm³ and Z=1. Refinement using 2222 reflections for 157 variables gives R=0.037. Crystals of diselenide 2 are triclinic, space group P1 with a=9.1418(8) Å, b=9.1465(8) Å, c=9.9200(9) Å, =74.751(8)°, β=74.629(7)°, γ=82.216(7)°, V=769.7(1) ų, D_c=1.365(2) g/cm³ and Z=1. Refinement using 3316 reflections for 297 variables gives R=0.0272.     

Determination of the (Na+) Sternheimer antishielding factor by 23Na NMR spectroscopy on sodium oxide chloride, Na3OCl

The (Na⁺) Sternheimer antishielding factor γ_∞ (Na⁺) was determined by ²³Na NMR spectroscopy on sodium oxide chloride, Na₃OCl. The quadrupolar coupling constant of the sodium ion in Na₃OCl was determined to QCC=11.34 MHz, which presents the largest coupling constant of a sodium nucleus observed so far. Applying a simple point charge model, the largest principal value of the electric field gradient at the sodium site was calculated to V_zz=−6.76762·10²⁰ V/m². From these values we calculated the (Na⁺) Sternheimer antishielding factor to γ_∞ (Na⁺)=−5.36. In sodium oxide, Na₂O, we observed an isotropic chemical shift of δ_CS=55.1 ppm, referenced to 1 M aqueous NaCl (δ=0 ppm).     

27Al NMR study in UNiAl

The ternary compound UNiAl exhibiting an antiferromagnetic order below T_N = 19.3 K has been studied in the paramagnetic state using the ²⁷Al NMR technique and different magnetically oriented samples. The quadrupole coupling constant e²qQ/h = 1.56 MHz is temperature independent. The dominant, longitudinal component of the Knight shift with respect to the hexagonal c axis, K, is positive and increases upon lowering the temperature down to 50 K. Much smaller in magnitude, the transverse component, K_±, is also positive and only slightly temperature dependent. The plots of the Knight shift vs magnetic susceptibility K(χ) and K_±(χ_±) form the same line, which implies that the transferred hyperfine field of 9.2 kOe/μB for ²⁷Al nuclei should be considered isotropic.     

29Si and 19F MAS NMR spectra of isolated 29Si(19F)2 and 29Si(19F)3 spin systems: experiments and simulations

We consider ²⁹Si and ¹⁹F MAS NMR spectra of isolated ²⁹Si(¹⁹F)₂ and ²⁹Si(¹⁹F)₃ spin systems in two organosilicon compounds of the type RR’SiF₂ and RSiF₃(R,R′=organic ligands). Experimental spectra are analysed by means of numerical simulations. It is found that the SiF₃ group in RSiF₃ is reorienting rapidly around the molecular Si–C bond direction in the solid state. The two ¹⁹F shielding tensors in RR’SiF₂ have strongly differing orientations relative to the two Si–F bond directions in the molecule. Possibilities and limitations of straightforward MAS NMR approaches for the full characterisation of ²⁹Si(¹⁹F)₂ and ²⁹Si(¹⁹F)₃ spin systems and other dipolar coupled two and three-spin systems are discussed.     

Unusual observation of nitrogen chemical shift anisotropies in tetraalkylammonium halides by 14N MAS NMR spectroscopy

¹⁴N Magic-angle spinning (MAS) NMR spectra for a number of polycrystalline, symmetrical tetraalkylammonium halides with short alkyl chains (C₂H₅– to n-C₄H₉–) have been recorded following a careful setup of the experimental conditions. Analysis of the spectra demonstrates the presence of ¹⁴N chemical shift anisotropies (CSAs) on the order of |δ_σ|=10–30 ppm along with ¹⁴N quadrupole coupling constants in the range of 10–70 kHz. The magnitude and sign of the CSAs determined from ¹⁴N MAS NMR are confirmed by recording and analysis of the corresponding slow-speed spinning (500–650 Hz) ¹⁵N CP/MAS NMR spectra. Most interestingly, it is observed experimentally and demonstrated theoretically and by simulations, that these CSAs are reflected in the spinning sideband (ssb) intensities of the ¹⁴N MAS spectra at much higher spinning speeds than can be applied to retrieve the corresponding ¹⁵N CSAs from the ssb pattern in the ¹⁵N CP/MAS spectra.     

From crystalline to glassy gallium fluoride materials: an NMR study of Ga and Ga quadrupolar nuclei

Owing to the implementation of acquisition techniques specific for nuclei with very large quadrupolar interaction (full shifted echo and variable offset cumulative spectra (VOCS)), NMR spectra of ⁶⁹Ga and ⁷¹Ga are obtained in crystallised (PbGaF₅, Pb₃Ga₂F₁₂, Pb₉Ga₂F₂₄ and CsZnGaF₆) and glassy (PbF₂–ZnF₂–GaF₃) gallium fluorides. Simulations of both static (full echo or VOCS) and 15 kHz MAS spectra allow to obtain consistent determinations of isotropic chemical shifts and very large quadrupolar parameters (ν_Q up to 14 MHz). In the crystalline compounds whose structures are unknown, the number and the local symmetry of the different gallium sites are tentatively worked out. For the glassy systems, a continuous Czjzek's distribution of the NMR quadrupolar parameters accounts for the particular shape of the NMR spectrum.     

H MAS and H[Na] double resonance NMR studies on the modification of surface hydroxyl groups of γ-alumina by sodium

The modification of surface hydroxyl groups with sodium in a series of Na₂CO₃-γ-Al₂O₃ catalysts was investigated as a function of both the Na₂CO₃ loading and the calcination temperature by means of ¹H magic angle spinning (MAS) and ¹H[²³Na] spin-echo double resonance NMR techniques. The ¹H NMR experiments revealed that sodium ions are homogeneously distributed over the alumina surface and closely coordinated with the surface hydroxyl groups. In the catalysts calcined at 250 °C, the acidic hydroxyl groups (with a chemical shift of 2.0 ppm) are preferentially associated with sodium ions at low Na₂CO₃ coverages (5 and 10%), while both the acidic and the basic (0 ppm) hydroxyl groups are accessible for sodium ions at high coverages (15 and 20%). The coordination causes a low-field shift of about 2 ppm in the ¹H MAS spectra, and a broad signal at 4.5 ppm appears. It is interesting that the 4.5 ppm signal is completely suppressed in the ¹H[²³Na] MAS experiments, providing direct evidence that a strong interaction exists between adsorbed sodium ions and the surface hydroxyl groups. Increasing the calcination temperature to 450 °C results in preferential removal of the acidic hydroxyl groups, and only the most basic hydroxyl groups remain when the calcination temperature is raised to 600 °C. This is attributed to the formation of the coordinated species which enhances the acidity of the surface hydroxyl groups and prompts their dehydroxylation, especially at high calcination temperature. Correlation of the ¹H MAS NMR results and catalytic activity measurements indicates that the basic hydroxyl groups are essential for the carbonyl sulfide hydrolysis reaction.     

Short-range order and F ion diffusion inside the Pb1 − xAlxF2 + x solid solution Part II: Al NMR investigation and proposal of clustering process

A ²⁷Al nuclear magnetic resonance (NMR) investigation at room temperature of the Pb_{1 − x}Al_xF_{2 + x} (0 ≤ x ≤ 0.12) solid solution and of the ordered Pb₉Al₂F₂₄ phase is carried out. Two different types of aluminium ions are identified and their ratio is determined as a function of x. A clustering process based on the formation of column clusters, more and more extended when x increases, is proposed on the basis of results issued from the ¹⁹F (Part I) and ²⁷Al NMR investigations.