丝光沸石水蒸气/酸浸渍脱铝的多核固体核磁共振研究

采用¹H,²⁹Si,²⁷Al魔角旋转固体核磁共振(MASNMR)及¹H-²⁹Si交叉极化(CP)技术研究丝光沸石水蒸气/酸浸渍脱铝过程中各种铝物质的结构与性质.结果表明,丝光沸石上骨架铝原子在水分子作用下,生成非骨架四配位铝物质[Al(OH)₃(H₂O)],分别在²⁷Al谱δ45和¹H谱δ3.0处出现共振信号,这种铝物质不同于扭曲四配位铝,在高温下进一步水合生成Al(OH)₃(H₂O)₂和Al(OH)₃(H₂O)₃,即非骨架五配位和六配位铝物质.¹H-²⁹SiCP和¹H谱证实,水蒸气脱铝使丝光沸石产生了大量的硅羟基和铝羟基.     

High-pressure delta-Al(OH)3 and delta-AlOOH phases and isostructural hydroxides/oxyhydroxides: new structural insights from high-resolution 1H and 27Al NMR

In order to shed light on the proton distributions and order/disorder in high-pressure delta-Al(OH)3 and delta-AlOOH phases, two-dimensional, high-resolution 1H CRAMPS (FSLG)-MAS NMR and 27Al 3QMAS NMR spectra have been obtained. For delta-Al(OH)3, the 1H CRAMPS-MAS NMR revealed two peaks with an intensity ratio close to 2:1. The 27Al MAS and 3QMAS NMR suggest a single Al site with a well-defined local structure. For delta-AlOOH, the 1H and 27Al NMR indicate the presence of a single H and Al site each. These results are consistent with crystal structures refined from X-ray diffraction. For comparison, 1H MAS and CRAMPS-MAS NMR spectra were also obtained for several other hydroxides/oxyhydroxides, including In(OH)3 and InOOH that have similar structures to delta-Al(OH)3 and delta-AlOOH, respectively. These data not only provide additional insights into the proton distributions in these important crystal structure classes but also together provide a better defined quantitative correlation between 1H chemical shift and hydrogen-bonding O...O distance.     

Indium and aluminium-doped ZnO thin films deposited onto FTO substrates: nanostructure,optical, photoluminescence and electrical properties

The microstructure, optical, photoluminescence and electrical properties of ZnO based films deposited onto FTO glass substrates by ultrasonic spray pyrolysis have been investigated. For comparison and a better understanding of physical properties of indium- and aluminum-doped ZnO and undoped ZnO thin films, X-ray diffraction analysis, photoluminescence spectra, optical, SEM texture and electrical conductivity analyses were performed. The AZO and IZO films exhibit the nanofiber structure with diameters 260 and 400 nm. X-ray diffraction showed all samples to be polycrystalline with hexagonal ZnO. The optical band gaps of the films were varied by Al and In dopants. The photoluminescence spectra of the films show a weak broad in the visible range and shifted to green emission for indium doping and to the green blue emission for aluminum as dopant. The width of the PL spectra for aluminum-doped films is too large compared to those of the indium-doped ones. The electrical conductivity of the ZnO film changes with Al and In dopants. The position of donor levels changes with In and Al dopants and approaches the conduction band level with the metal dopants. The obtained results suggest that the metal doping has a clear effect upon the growth, optical, photoluminescence and electrical conductivity properties of the ZnO films.     

Multinuclear solid-state high-resolution and 13C -{27Al} double-resonance magic-angle spinning NMR studies on aluminum alkoxides

A combination of 27Al magic-angle spinning (MAS)/multiple quantum (MQ)-MAS, 13C-1H CPMAS, and 13C-{27Al} transfer of population in double-resonance (TRAPDOR) nuclear magnetic resonance (NMR) were used for the structural elucidation of the aluminum alkoxides aluminum ethoxide, aluminum isopropoxide, and aluminum tertiarybutoxide. Aluminum alkoxides exist as oligomers with aluminum in different coordinations. High-resolution 27Al MAS NMR experiments with high-spinning speed distinguished the aluminum atoms in different environments. The 27Al MAS NMR spectrum gave well-resolved powder patterns with different coordinations. Z-filter MQ-MAS was performed to obtain the number and types of aluminum environments in the oligomeric structure. 13C-1H CPMAS chemical shifts resolved the different carbon species (-CH3, =CH2, =CH-, and =C=) in the structures. 13C-{27Al} TRAPDOR experiments were employed to obtain relative Al-C dipolar interactions and to distinguish between terminal and bridging alkoxides in the crystallographic structures. The complete characterization of selected aluminum alkoxides using advanced NMR methods has evidenced the tetrameric structure for aluminum isopropoxide and the dimeric structure for aluminum tertiary-butoxide, as reported in the literature, and proposed a polymeric structure for aluminum ethoxide.     

Solid-state NMR detection, characterization, and quantification of the multiple aluminum environments in US-Y catalysts by (27)Al MAS and MQMAS experiments at very high field.

The detection of all of the aluminum present in steamed zeolite H-Y catalysts by (27)Al MAS NMR at 14.4 T (600 MHz for (1)H) and 18.8T (800 MHz for (1)H) is reported. Further, it is shown that it is possible by (27)Al MAS and MQMAS NMR measurements to clearly identify four separate aluminum environments which are characteristic of these materials and to unambiguously assign their coordinations. Average chemical shift and quadrupolar coupling parameters are used to accurately simulate the (27)Al MAS NMR spectra at 9.4 T (400 MHz for (1)H), 14.4 T (600 MHz for (1)H) and 18.8 T (800 MHz for (1)H) in terms of these four aluminum environments. In addition, these average chemical shift and quadrupolar coupling parameters are used to calculate peak positions in the (27)Al MQMAS isotropic dimension that are in good agreement with the experimental data acquired at 9.4 and 18.8 T.     

层状磷酸铝UT-4的固体核磁共振研究

用吡啶代替四乙二醇作为溶剂, 在Al2O3-H3PO4-C6H11NH2-Py体系下合成出层状阴离子骨架磷酸铝［Al2P3O12H］2-·2［C6H11NH+3］(UT-4)的纯晶相, 采用一维27Al， 31P MAS NMR , 1H→31P CP(Cross Polarization)以及二维27Al- 31P HETCOR(Heteronuclear Correlation)高分辨固体核磁共振技术对其骨架结构进行了表征. 采用两种方法对 27Al信号进行了归属, 并通过分析27Al-31P HETCOR谱对31P 信号进行了归属.     

New crystalline aluminum alkoxide oxide fluorides: evidence of the mechanism of the fluorolytic sol-gel reaction

This study reports three new crystalline aluminum isopropoxide oxide fluorides with molar ratios of Al:F equal to 1:1 and 1:1.25. These are the first three representatives isolated without the incorporation of external donor molecules. Compound 1 Al(4)F(4)(μ(4)-O)(μ-O(i)Pr)(5)[H(O(i)Pr)(2)] contains a tetranuclear unit consisting of two different five fold coordinated AlFO(4)-units, with F exclusively in the terminal position. Compound 2, Al(4)F(4)(μ(4)-O)(μ-O(i)Pr)(5)[H(O(i)Pr)(2)]·Al(5)F(5)(μ(5)-O)(μ-O(i)Pr)(8), contains both a tetranuclear unit (as in 1) and a pentanuclear Al-unit. Al-atoms in the latter are five- and six fold coordinated. Compound 3, Al(16)F(20)(μ(4)-O)(4)(μ-O(i)Pr)(20)·2((i)PrOH), exhibits a slightly higher fluorination degree and contains an oligomeric chain of four F-linked tetranuclear Al-units. In addition to X-ray structure analysis, compound 1 was characterized by different solid state MAS NMR techniques, including (27)Al triple quantum MAS NMR and (1)H, (1)H→(13)C CP, (19)F and (27)Al MAS NMR. On the basis of the collected data, a reliable decomposition of (27)Al single pulse MAS NMR spectra and an unambiguous assignment of the resonances to the respective structural AlFO(4)-units are given. The new crystalline aluminum isopropoxide oxide fluorides are direct evidence of the fluorolytic sol-gel mechanism previously discussed.     

Incorporation of aluminum in the calcium silicate hydrate (C-S-H) of hydrated portland cements: a high-field 27Al and 29Si MAS NMR investigation

The calcium silicate hydrate (C-S-H) phase resulting from hydration of a white Portland cement (wPc) in water and in a 0.3 M NaAlO(2) solution has been investigated at 14 and 11 hydration times, respectively, ranging from 6 h to 1 year by (27)Al and (29)Si MAS NMR spectroscopy. (27)Al MAS NMR spectra recorded at 7.05, 9.39, 14.09, and 21.15 T have allowed a determination of the (27)Al isotropic chemical shift (delta(iso)) and quadrupolar product parameter (P(Q) = C(Q)) for tetrahedrally coordinated Al incorporated in the C-S-H phase and for a pentacoordinated Al site. The latter site may originate from Al(3+) substituting for Ca(2+) ions situated in the interlayers of the C-S-H structure. The spectral region for octahedrally coordinated Al displays resonances from ettringite, monosulfate, and a third aluminate hydrate phase (delta(iso) = 5.0 ppm and P(Q) = 1.20 MHz). The latter phase is tentatively ascribed to a less-crystalline aluminate gel or calcium aluminate hydrate. The tetrahedral Al incorporated in the C-S-H phase has been quantitatively determined from (27)Al MAS spectra at 14.09 T and indirectly observed quantitatively in (29)Si MAS NMR spectra by the Q(2)(1Al) resonance at -81.0 ppm. A linear correlation is observed between the (29)Si MAS NMR intensity for the Q(2)(1Al) resonance and the quantity of Al incorporated in the C-S-H phase from (27)Al MAS NMR for the different samples of hydrated wPc. This correlation supports the assignment of the resonance at delta(iso)((29)Si) = -81.0 ppm to a Q(2)(1Al) site in the C-S-H phase and the assignment of the (27)Al resonance at delta(iso)((27)Al) = 74.6 ppm, characterized by P(Q)((27)Al) = 4.5 MHz, to tetrahedrally coordinated Al in the C-S-H. Finally, it is shown that hydration of wPc in a NaAlO(2) solution results in a C-S-H phase with a longer mean chain length of SiO(4) tetrahedra and an increased quantity of Al incorporated in the chain structure as compared to the C-S-H phase resulting from hydration of wPc in water.     

Structural insights into aluminum chlorofluoride (ACF)

The structure of the very strong solid Lewis acid aluminum chlorofluoride (ACF, AlCl(x)F(3-x), x = 0.05-0.3) was studied by IR, ESR, Cl K XANES, (19)F MAS NMR, and (27)Al SATRAS NMR spectroscopic methods and compared with amorphous aluminum fluoride conventionally prepared by dehydration of alpha-AlF(3) x 3H(2)O. The thermal behavior of both compounds was investigated by DTA and XRD. In comparison to ACF, amorphous AlF(3) prepared in a conventional way is not catalytically active for the isomerization reaction of 1,2-dibromohexafluoropropane, which requires a very strong Lewis acid. Both compounds are mainly built up of corner-sharing AlF(6) octahedra forming a random network. The degree of disorder in ACF is higher than in amorphous AlF(3). Terminal fluorine atoms were detected in ACF by (19)F NMR. The chlorine in ACF does not exist as a separate, crystalline AlCl(3) phase. Additionally, chlorine-containing radicals, remaining from the synthesis, are trapped in cavities of ACF. These radicals are stable at room temperature but do not take part in the catalytic reaction.     

Characterization of nanosized ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> spinel synthesized by the sol–gel method

Single-phase zinc aluminate (ZnAl₂O₄) nanoparticles with the spinel structure was successfully obtained by the sol–gel method. The nanoparticles are crystalline with no impurities related to ZnO or Al₂O₃ residues. The microstructural environment of aluminum ions changes with heat treatment temperature, as observed by FT-IR and also by ²⁷Al solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) spectra. The photoluminescence spectra show that the emission of pristine ZnAl₂O₄ may change depending on the calcining temperature due to the quantum size effect.     

HZSM-5分子筛焙烧脱铝的27Al MQMAS NMR研究

用29Si、27Al魔角旋转固体核磁共振(MAS NMR)结合二维多量子魔角旋转(2D MQMAS)技术对焙烧脱铝的HZSM-5分子筛中铝的配位状态进行了研究.结果表明,HZSM-5分子筛经焙烧后,在化学位移(δ)45处出现一宽峰信号,其主要来自扭曲四配位铝.通过二维三量子铝谱计算出扭曲四配位铝的四极作用常数约为5.2 MHz.对700和750 ℃焙烧样品的铝谱进行分峰拟合,发现在δ 30处又出现一个小峰,归属为非骨架五配位铝.同时,在750 ℃焙烧样品的二维多量子铝谱中直接观察到非骨架五配位铝的信号.焙烧温度低于700 ℃,脱铝不明显；高于700 ℃,引起分子筛骨架的显著脱铝.焙烧还造成部分骨架铝的信号变得“不可观测”.     

Aluminum orthovanadate (AlVO4): synthesis and characterization by (27)Al and 51V MAS and MQMAS NMR spectroscopy

Polycrystalline samples of AlVO(4) have been prepared by two methods of synthesis and characterized by (27)Al and (51)V MAS NMR spectroscopy at 14.1 T. The MAS NMR spectra clearly reveal that essentially pure samples with minor impurities of V(2)O(5) and alumina have been obtained. From these samples, (27)Al quadrupole coupling parameters and isotropic chemical shifts as well as the magnitudes and relative orientations of the (51)V quadrupole coupling and chemical shift tensors have been determined with high precision for AlVO(4). These data have been obtained from a combined analysis of multiple-quantum (MQ) MAS NMR spectra and MAS NMR spectra of the central and satellite transitions. The (27)Al and (51)V NMR data show that the asymmetric unit for AlVO(4) contains three isolated VO(4) tetrahedra, one pentacoordinated Al site, and two AlO(6) octahedra. This is in agreement with the supposition that AlVO(4) is isostructural with FeVO(4) and with a recent structure refinement for AlVO(4) based on powder X-ray diffraction (XRD) data. The favorable agreement between the refined crystal structure from powder XRD and the NMR parameters is apparent from a convincing correlation between experimental (51)V quadrupole tensor elements and calculated (51)V electric field gradient tensor elements obtained by the point-monopole approach. An assignment of the (27)Al NMR data is obtained from similar calculations of the (27)Al electric field gradients and by estimation of the distortion of the AlO(6) octahedra.     

Solid-state NMR spectra of paramagnetic silica-based materials: observation of 29Si and 27Al nuclei in the first coordination spheres of manganese ions

Some silica-based solids, prepared by the sol/gel method in the presence of high Mn2+ concentrations, have been characterized by the 29Si, 27Al MAS NMR spectra and 29Si T1 measurements. The single-pulse 29Si and 27Al MAS NMR spectra have shown broad spinning sideband patterns that are interpreted in terms of anisotropic bulky magnetic susceptibility (BMS) and dipole-field effects. In the absence of paramagnetic isotropic shifts, the 29Si and 27Al nuclei observed in the single-pulse NMR spectra have been assigned to nuclei remote from paramagnetic centers. It has been demonstrated that the 29Si and 27Al nuclei, which are in the vicinity of the manganese ions, can be detected by the Hahn-echo MAS NMR experiments at different carrier frequencies.     

Multinuclear solid-state NMR spectroscopy of doped lanthanum fluoride nanoparticles

Multinuclear solid-state NMR spectroscopy and powder X-ray diffraction (XRD) experiments are applied to comprehensively characterize a series of pure and lanthanide-doped LaF3 nanoparticles (NPs) that are capped with di-n-octadectyldithiophosphate ligands (Ln3+ = diamagnetic Y3+ and Sc3+ and paramagnetic Yb3+ ions), as well as correlated bulk microcrystalline materials (LaF3, YF3, and ScF3). Solid-state 139La and 19F NMR spectroscopy of bulk LaF3 and the LaF3 NPs reveal that the inorganic core of the NP retains the LaF3 structure at the molecular level; however, inhomogeneous broadening of the NMR powder patterns arises from distributions of 139La and 19F NMR interactions, confirming a gradual change in the La and F site environments from the NP core to the surface. 139La and 19F NMR experiments also indicate that low levels (5 and 10 mol %) of Ln3+ doping do not significantly change the LaF3 structure in the NP core. Similar doping levels of paramagnetic Yb3+ ions severely broaden 19F resonances, but only marginally effect 139La powder patterns, suggesting that the dopant ions are uniformly distributed throughout the NP core and occupy vacant La sites. Measurements of 139La T1 and T2 relaxation constants are seen to vary between the bulk material and NPs and between samples with diamagnetic and paramagnetic dopants. 45Sc NMR experiments confirm that the dopants are integrated into the La sites of the LaF3 core. Solid-state 1H and 31P magic-angle spinning (MAS) NMR spectra aid in probing the nature of the capping ligands and their interactions at the NP surface. 31P cross-polarization (CP)/MAS NMR experiments identify not only the dithiophosphate head groups but also thiophosphate and phosphate species which may form during NP synthesis. Finally, 19F-31P CP/MAS and 1H MAS experiments confirm that ligands are coordinated to the NP surface.     

Factor analysis of 27Al MAS NMR spectra for identifying nanocrystalline phases in amorphous geopolymers

Nanostructured materials offer enhanced physicochemical properties because of the large interfacial area. Typically, geopolymers with specifically synthesized nanosized zeolites are a promising material for the sorption of pollutants. The structural characterization of these aluminosilicates, however, continues to be a challenge. To circumvent complications resulting from the amorphous character of the aluminosilicate matrix and from the low concentrations of nanosized crystallites, we have proposed a procedure based on factor analysis of ²⁷Al MAS NMR spectra. The capability of the proposed method was tested on geopolymers that exhibited various tendencies to crystallize (i) completely amorphous systems, (ii) X‐ray amorphous systems with nanocrystalline phases, and (iii) highly crystalline systems. Although the recorded ²⁷Al MAS NMR spectra did not show visible differences between the amorphous systems (i) and the geopolymers with the nanocrystalline phase (ii), the applied factor analysis unambiguously distinguished these materials. The samples were separated into the well‐defined clusters, and the systems with the evolving crystalline phase were identified even before any crystalline fraction was detected by X‐ray powder diffraction. Reliability of the proposed procedure was verified by comparing it with ²⁹Si MAS NMR spectra. Factor analysis of ²⁷Al MAS NMR spectra thus has the ability to reveal spectroscopic features corresponding to the nanocrystalline phases. Because the measurement time of ²⁷Al MAS NMR spectra is significantly shorter than that of ²⁹Si MAS NMR data, the proposed procedure is particularly suitable for the analysis of large sets of specifically synthesized geopolymers in which the formation of the limited fractions of nanocrystalline phases is desired. Copyright © 2013 John Wiley & Sons, Ltd.     

Heteronuclear NMR Spectroscopy as a Surface‐Selective Technique: A Unique Look at the Hydroxyl Groups of γ‐Alumina.

The surface hydroxyl groups of γ‐alumina dehydroxylated at 500 °C were studied by a combination of one‐ and two‐dimensional homo‐ and heteronuclear ¹H and ²⁷Al NMR spectroscopy at high magnetic field. In particular, by harnessing ¹H–²⁷Al dipolar interactions, a high selectivity was achieved in unveiling the topology of the alumina surface. The terminal versus bridging character of the hydroxyl groups observed in the ¹H magic‐angle spinning (MAS) NMR spectrum was demonstrated thanks to ¹H–²⁷Al RESPDOR (resonance‐echo saturation‐pulse double‐resonance). In a further step the hydroxyl groups were assigned to their aluminium neighbours thanks to a {¹H}‐²⁷Al dipolar heteronuclear multiple quantum correlation (D‐HMQC), which was used to establish a first coordination map. Then, in combination with ¹H–¹H double quantum (DQ) MAS, these elements helped to reveal intimate structural features of the surface hydroxyls. Finally, the nature of a peculiar reactive hydroxyl group was demonstrated following this methodology in the case of CO₂ reactivity with alumina.     

Structural characterization of moganite-type AlPO4 by NMR and powder X-ray diffraction

Structural characterization of a new high-pressure AlPO(4) phase synthesized at 5 GPa and 1500 °C is reported. The phase is monoclinic (P2/a) with a = 8.7437(1) ?, b = 4.8584(1) ?, c = 10.8600(2) ?, β = 90.124(1)° (Z = 6). (31)P MAS NMR and two-dimensional (2D) (27)Al triple-quantum (3Q) MAS NMR revealed that it contains two tetrahedral P sites of 1:2 abundance ratio, and two tetrahedral Al sites with 1:2 ratio. 2D (31)P dipolar-recoupled double-quantum (DQ) MAS NMR and (27)Al → (31)P dipolar-based (through-space) and J coupling-based (through-bond) 3Q-heteronuclear correlation (HETCOR) experiments provided direct information on the linkages of these sites. The crystal structure was solved and refined from synchrotron powder X-ray diffraction data utilizing the information from NMR. The phase is isostructural to moganite, a rare SiO(2) polymorph, and its structure can be derived from the latter via an ordered replacement of tetrahedral Si sites by Al and P. The NMR parameters of the phase were also calculated by first-principles method, which are consistent with those observed. Contrary to the other moganite phases known to date (i.e., SiO(2) and PON), moganite-AlPO(4) has a higher-pressure stability field than the corresponding quartz phase. This is the first moganite-type phase found in the ABX(4) system.     

Towards guest-zeolite interactions: an NMR spectroscopic approach

Guest(metal)-zeolite interactions in a two component heterogeneous catalyst have been investigated by high-field and high-speed (27)Al MAS NMR, and two-dimensional (27)Al MQ MAS NMR experiments as well as ab initio DFT methods. It was established that strong interactions between guest and zeolite occur in a metal/zeolite system, with the metal anchored to the tetrahedral aluminum framework site through two oxygen bridges. It disturbs the tetrahedral environment of associated aluminum framework, changing AlO(4) geometry from near T(d) to C(2v); this enables us to resolve this species from the undisturbed aluminum framework species in high-field (27)Al MAS NMR and two-dimesional (27)Al MQ MAS NMR experiments.     

Hydrogen bonds and local symmetry in the crystal structure of gibbsite

First‐principles quantum mechanical calculations of NMR chemical shifts and quadrupolar parameters have been carried out to assign the ²⁷Al MAS NMR resonances in gibbsite. The ²⁷Al NMR spectrum shows two signals for octahedral aluminum revealing two aluminum sites coordinated by six hydroxyl groups each, although the crystallographic positions of the two Al sites show little difference. The presence of two distinguished ²⁷Al NMR resonances characterized by rather similar chemical shifts but quadrupolar coupling constants differing by roughly a factor of two is explained by different character of the hydrogen bonds, in which the hydroxyls forming the corresponding octahedron around each aluminum site, are involved. The Al‐I site characterized by a C_Q = 4.6 MHz is surrounded by OH? groups participating in four intralayer and two interlayer hydrogen bonds, while the Al‐II site with the smaller quadrupolar constant (2.2 MHz) is coordinated by hydroxides, of which two point toward the intralayer cavities and four OH‐bonds are aligned toward the interlayer gallery. In high‐resolution solid‐state ¹H CRAMPS (combination of rotation and multiple‐pulse spectroscopy) four signals with an intensity ratio of 1:2:2:1 are resolved which allow to distinguish six nonequivalent hydrogen sites reported in the gibbsite crystal structure and to ascribe them to two types of structural OH groups associated with intralayer and interlayer hydrogen bonds. This study can be applied to characterize the gibbsite‐like layer—intergallery interactions associated with hydrogen bonding in the more complex systems, such as synthetic aluminum layered double hydroxides. Copyright © 2010 John Wiley & Sons, Ltd.