New synthesis of mullite. Structural evolution study by 17O, 27Al and 29Si MAS NMR spectroscopy

Mullite has been prepared from a new combination of precursors. An aluminum alkoxide, aluminium isopropoxide, and silicon tetrachloride, are hydrolysed in tetrahydrofuran solution by ¹⁷O enriched water. The resulting powder is chemically homogeneous, crystallizing into mullite at 980°C. The structural evolution has been studied by DTA, TGA, XRD and ¹⁷O, ²⁷Al and ²⁹Si MAS NMR spectroscopy.     

Reactivity of Extra‐framework Species of USY Zeolites in Alkaline Medium

Zeolites of type USY (ultra‐stable Y) were obtained by steaming of NH₄NaY modification. Samples were modified by subsequent alkaline treatment in KOH solution. USY and USY‐KOH were characterised by chemical element analysis, XRD, IR, ²⁹Al and ²⁹Si MAS NMR spectroscopic measurements. Correct silicon to aluminium ratios (Si/Al) were determined by XRD and IR (double ring vibration w_DR) data whereas values calculated according to data of ²⁹Si MAS NMR and IR spectroscopy (asymmetrical TOT valence vibration w_TOT) appeared to be too high., In the latter case, the signals of the zeolite framework were strongly superimposed by that of extra‐framework silica gel (EFSi) formed during steaming. It was found that alkaline leaching induces desilication of silicon‐rich area of the zeolite framework and partial dissolution of EFSi. Silicate ions of both react with likewise dissolved extra‐framework aluminium (EFAl) to form X‐ray amorphous aluminosilicate. Consequently, the superposition of the ²⁹Si MAS NMR signals of the zeolite framework by silica gel was reduced for Q⁴(0Al) but increased for Q⁴ (2Al) and Q⁴(3Al) structure units. A reinsertion of EFAl into the zeolite framework has not been observed.     

Ω型分子筛脱铝的核磁共振研究

在不同投料比（ＳｉＯ２／Ａｌ２Ｏ３＝１３．８，１９及２１）条件下，合成了三种Ω型分子筛原粉．对投料比为１３．８的原粉样品进行了四种不同方式的脱铝处理，即水热、ＳｉＣｌ４、ＥＤＴＡ和（ＮＨ４）２ＳｉＦ６处理，而形成了系列脱铝Ω型分子筛样品．对原粉及其脱铝样品进行了２９Ｓｉ和２７ＡｌＭＡＳＮＭＲ测试，确定出样品骨架硅铝比和铝在两种晶体学不等价Ｔ位上的占据比率，以探索四种脱铝方法的效果．实验结果与分析表明：在所有样品中，铝原子的占据具有择优Ｂ位的倾向；且铝在ＴＡ与ＴＢ位上的占据比率与合成条件有关；四种处理方式对Ω型分子筛的脱铝效果不尽相同．     

Magic-Angle-Spinning NMR (MAS-NMR) Spectroscopy and the Structure of Zeolites

After outlining the chemical features and properties which make zeolites such an important group of catalysts and sorbents, the article explains how high-resolution solid-state NMR with magic-angle spinning reveals numerous new insights into their structure. ²⁹Si-MAS-NMR readily and quantitatively identifies five distinct Si(OAl)_n(OSi)_4-n structural groups in zeolitic frameworks (n = 0, 1,….4), corresponding to the first tetrahedral coordination shell of a silicon atom. Many catalytic and other chemical properties of zeolites are governed by the short-range Si, Al order, the nature of which is greatly clarified by ²⁹Si-MAS-NMR. It is shown that, as expected from Pauling's electroneutrality principle and Loewenstein's rule, both in zeolite X and in zeolite A (with Si/Al = 1.00) there are no ? Al? O? Al? linkages. In zeolite A and zeolite X with Si/Al = 1.00 there is strict alternation of Si and Al on the tetrahedral sites. Ordering models for Si/Al ratios up to 5.00 (in zeolite Y) may also be evaluated by a combination of MAS-NMR experiments and computational procedures. ²⁹Si-MAS-NMR spectra reveal the presence of numerous crystallographically distinct Si(OSi)₄ sites in silicalite/ZSM-5, suggesting that the correct space group for these related porosilicates is not Pnma. ²⁷Al-MAS-NMR clearly distinguishes tetrahedrally and octahedrally coordinated aluminum, proving that, contrary to earlier claims, Al in silicalite is tetrahedrally substituted within the framework. In combination, ²⁹Si- and ²⁷Al-MAS-NMR is a powerful tool for monitoring the course of solid-state processes (such as ultrastabilization of synthetic faujasites) and of gas-solid reactions (dealumination of zeolites with silicon tetrachloride vapor at elevated temperatures). They also permit the quantitative determination of framework Si/Al ratios in the region 1.00 < Si/Al < 10 000. Since most elements in the periodic table may be accommodated within zeolite structures, either as part of the exchangeable cations or as building units of the anionic framework, there is immense scope for investigation by MAS-NMR and its variants (cross-polarization, multiple pulse and variable-angle spinning) of bulk, surface and chemical properties. Some of the directions in which future research in zeolite science may proceed are adumbrated.     

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.     

High magnetic field solid‐state NMR analyses by combining MAS,MQ‐MAS,homo‐nuclear and hetero‐nuclear correlation experiments

A general strategy of structural analysis of alumina silicate by combining various solid‐state NMR measurements such as single pulse, multi‐quantum magic angle spinning, double‐quantum homo‐nuclear correlation under magic angle spinning (DQ‐MAS), and cross‐polarization hetero‐nuclear correlation (CP‐HETCOR) was evaluated with the aid of high magnetic field NMR (800 MHz for ¹H Larmor frequency) by using anorthite as a model material. The high magnetic field greatly enhanced resolution of ²⁷Al in single pulse, DQ‐MAS, and even in triple‐quantum magic angle spinning NMR spectra. The spatial proximities through dipolar couplings were probed by the DQ‐MAS methods for homo‐nuclear correlations between both ²⁷Al–²⁷Al and ²⁹Si–²⁹Si and by CP‐HETCOR for hetero‐nuclear correlations between ²⁷Al–²⁹Si in the anorthite framework. By combining various NMR methodologies, we elucidated detailed spatial correlations among various aluminum and silicon species in anorthite that was hard to be determined using conventional analytical methods at low magnetic field. Moreover, the presented approach is applicable to analyze other alumina‐silicate minerals. Copyright © 2012 John Wiley & Sons, Ltd.     

Solid-state Al and Si NMR characterization of hydrates formed in calcium aluminate-silica fume mixtures

Partially deuterated Ca₃Al₂(SiO₄)_y(OH)_12−4y-Al(OH)₃ mixtures, prepared by hydration of Ca₃Al₂O₆ (C₃A), Ca₁₂Al₁₄O₃₃ (C₁₂A₇) and CaAl₂O₄ (CA) phases in the presence of silica fume, have been characterized by ²⁹Si and ²⁷Al magic-angle spinning-nuclear magnetic resonance (MAS-NMR) spectroscopies. NMR spectroscopy was used to characterize anhydrous and fully hydrated samples. In hydrated compounds, Ca₃Al₂(OH)₁₂ and Al(OH)₃ phases were detected. From the quantitative analysis of ²⁷Al NMR signals, the Al(OH)₃/Ca₃Al₂(OH)₁₂ ratio was deduced. The incorporation of Si into the katoite structure, Ca₃Al₂(SiO₄)_3−x(OH)_4x, was followed by ²⁷Al and ²⁹Si NMR spectroscopies. Si/OH ratios were determined from the quantitative analysis of ²⁷Al MAS-NMR components associated with Al(OH)₆ and Al(OSi)(OH)₅ environments. The ²⁹Si NMR spectroscopy was also used to quantify the unreacted silica and amorphous calcium aluminosilicate hydrates formed, C-S-H and C-A-S-H for short. From ²⁹Si NMR spectra, the amount of Si incorporated into different phases was estimated. Si and Al concentrations, deduced by NMR, transmission electron microscopy, energy dispersive spectrometry, and Rietveld analysis of both X-ray and neutron data, indicate that only a part of available Si is incorporated in katoite structures.     

Phase Transformations in Alkaline and Acid Leached Y Zeolites Dealuminated by Steaming

The steaming of zeolite Y (here at 873 K for 7 hours) leads to the formation of an amorphous aluminium aluminosilicate in addition to the dealuminated zeolite (DAY). An alkaline treatment of DAY causes the transformation of the non‐framework phase into an alkali aluminosilicate and the partial desilication of the DAY framework. The alkali aluminosilicate is decomposed by a moderate acid leaching under the formation of silica gel. The ²⁹Si MAS NMR and IR spectra of DAY and its chemically treated modifications are superimposed by the signals of the crystalline zeolite framework and the amorphous non‐framework materials whereas XRD measurements only characterize the current state of the framework.     

The substitution of germanium for silicon in AST-type zeolite

The substitution of silicon by germanium in the AST zeolite framework type, [Si_nGe_40−nO₈₀]*4(SDA⁺F⁻) expressed as unit cell content in its cubic F-centered symmetry, has been studied. Three different kinds of templates, dimethyldiethylammonium, dimethyldiisopropylammonium and isopropyltrimethylammonium cations, were used in the hydrothermal synthesis process in fluoride medium. The products were identified with XRD, MAS NMR, SEM and thermal analysis. The analysis of the X-ray powder diagrams shows that AST crystallizes in different space group symmetries depending on the nature of the SDA and the degree of Ge-substitution. The resonance signals of ¹⁹F in MAS NMR experiments for the pure Si- and Ge-end members are at −38.2 and −15 ppm, respectively, indicating that the F⁻-anion is located as co-template in the double-four-ring (D4R) of the tetrahedral framework. This is confirmed by Rietveld analysis of powder diffraction data of the pure Ge-end member. The peak splitting of the ¹⁹F NMR signal in pure GeO₂AST-type material is related to the displacement of F⁻ location inside the D4R. Two more distinct signals at −8 and −19 ppm, respectively, are observed for X-ray pure AST-samples of intermediate compositions and assigned to fluoride in D4R built of 4[GeO₄]- and 4[SiO₄]-tetrahedra (4Ge, 4Si) and to (2Ge, 6Si)-D4R, respectively. An ordered distribution of Ge in the AST-framework is proposed for cubic AST with compositions around Si/Ge=1.5–1 by correlating the intensities of ¹⁹F NMR signals and the results from chemical analysis. This model is further confirmed by the quantitative analyses of the corresponding ²⁹Si MAS NMR spectra.     

^29Si（^27Al）MAS NMR考察镧离子在LaDAlY型沸石中的作用

用~(29)Si(~(27)Al)MAS NMR和辅加乙酰丙酮(acac)处理样品的静态~(27)Al NMR研究了镧离子对脱铝Y型沸石(DAIY)骨架硅、铝和非骨架铝(EFAL)的影响.结果表明,~(29)Si MAS谱的化学位移及其形状不仅取决于连接[SiO_4]四面体的[AlO]-四面体数目,而且还与引入镧离子的量有关.镧离子的引入导致~(27)Al MAS谱的明显宽化和不对称形变.另外,还讨论了镧离子对非骨架铝的影响.     

Solid-state NMR studies of framework defects in thermally treated zeolite Ca-A

²⁹Si, ²⁷Al and ¹H magic-angle-spinning NMR and relaxation measurements on thermally treated zeolite Na_3.2Ca_4.4-A have been carried out in order to study framework defects responsible for, and surface barriers to, molecular diffusion. Various possible mechanisms for the formation of such defects are considered in detail. We conclude that no framework dealumination takes place and no acidic hydroxyl groups are present in the zeolite. Excess aluminium occluded in the as-prepared zeolite A is responsible for the production of aluminium hydroxide during hydrothermal treatment.     

IR and29Si NMR investigation of the influence of alkaline modification on the structure of hydrothermally dealuminated Y zeolites

The change in the structure of NH₄NaY zeolite (53 % NH₄ ⁺, Si/Al = 2.37) after hydrothermal treatment at 873 K followed by modification with aqueous KOH solution at 353 K was studied by IR and²⁹Si NMR spectroscopy. It has been shown that hydrolytic cleavage of the Al-O bond of the deammoniated zeolite sites by hydrothermal treatment predominates in the framework groups Si(OAl) _n (OSi)_4–n ,n=2, 3. Molecular water adsorbed on such a sample exists as hydrogen-bonded associates with hydrogen bonds of various strengths reaching that in ice-like structures (the band at 2468 cm^–1). Treatment with an alkali results in partial regeneration of the normal bridge bonds. The exchange of the protons of the terminal silanol groups with the alkaline cation prevents those groups from participating in the regeneration process.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 387–391, March, 1994.     

Hybrid Organic-Inorganic Materials by Nonhydrolytic Sol-Gel Processes: Organosilsesquioxane-Metal Oxide Hybrids

Organosilsesquioxane-metal oxide hybrid materials prepared by the Sol-Gel process are mainly heterogeneous. In this paper we report the preparation of methylsilsesquioxane-titanium oxide, and methylsilsesquioxane-aluminium oxide hybrid materials by a nonhydrolytic sol-gel process involving the etherolysis-condensation of a mixture of methyltrichlorosilane and metal chloride. The Si/M ration in the xerogels were very closed to the one of the starting solutions. ²⁹Si MAS NMR study has revealed that the methylsilsesquioxane-titanium oxide xerogel was heterogeneous at the atomic level. The spectrum of the hybrid containing aluminium, has shown beside a peak at –66 ppm corresponding to MeSi(OSi)₃ environment, another peak at –47 ppm which was ascribed to MeSi(OAl)₃ environment. The presence of only these two sites might be due to their stability.     

焙烧对HZSM－5分子筛结构的影响

运用魔角自转固态核磁共振谱（ＭＡＳ－ＮＭＲ），研究了焙烧对ＨＺＳＭ－５分子筛结构的影响．结果表明，高温焙烧将引起ＨＺＳＭ－５分子筛骨架的脱铝，当焙烧温度从５００℃增加到７００℃时，ＨＺＳＭ－５的骨架Ｓｉ／Ａｌ比由１６．７增加至２２．７；而当焙烧温度由７００℃到８００℃时，骨架Ｓｉ／Ａｌ比则由２２．７增加到了４８．５．２７Ａｌ－ＭＡＳＮＭＲ结果表明，从骨架上脱下来的铝，部分地形成了ＮＭＲ不可见的无定形态．随着焙烧温度的升高，ＮＭＲ不可见铝增多     

Solid-state nuclear magnetic resonance investigation of synthetic phlogopite and lepidolite samples

In the present work, our aim is to decipher the cationic ordering in the octahedral and tetrahedral sheets of two Al-rich synthetic materials, namely, phlogopites of nominal composition K(Mg_3-xAl_x)[Al_1+xSi_3-xO₁₀](OH)_yF_2-y and lepidolites in the system trilithionite–polylithionite with composition K (Li_xAl_3-x)[Al_4-2xSi_2xO₁₀](OH)_yF_2-y, by directly probing the aluminium distribution through ²⁷Al and ¹⁷O magic-angle spinning, multiple-quantum magic-angle spinning, and ²⁷Al-²⁷Al double-quantum single-quantum nuclear magnetic resonance (NMR) experiments. Notably, ²⁷Al-²⁷Al double-quantum single-quantum magic-angle spinning NMR spectra, recorded at 9.34 and/or 20.00 T, show the spatial proximity or avoidance of the Al species inside or between the sheets. In both studied minerals, the ensemble of NMR data suggests a preference for ^[4]Al in the tetrahedral sheet to occupy position close to the ^[6]Al of the octahedral sheets.     

直接法合成ZSM—5型分子筛的物理化学表征

用高分辨~(29)Si、~(27)Al和~(23)Na NMR对直接法合成的不同硅铝比ZSM-5型分子筛局域结构作了表征,用~(29)Si和~(27)Al魔角旋转核磁共振研究了经不同温度水蒸气处理ZSM-5型分子筛的骨架脱铝,对不同条件下ZSM-5型分子筛中发生的正交-单斜晶型变化进行了系统的X射线衍射实验研究。     

Characterisation of Siliceous Extra‐Framework Species in DAY Zeolites by 29Si MAS NMR and IR Spectroscopic Measurements

Dealuminated Y zeolites (DAY) were obtained by steaming of NH₄NaY at temperatures between 450 °C and 700 °C. They were characterised by means of ²⁷Al and ²⁹Si MAS NMR, IR spectroscopic and XRD measurements. The Si/Al framework ratios of samples were calculated using the ²⁹Si MAS NMR signal intensities, the wave numbers of the double‐ring vibration band w_DR and the asymmetrical TOT valence vibration w_TOT of IR spectra as well as the XRD lattice constant a₀. In contrast to actual Si/Al ratio obtained from w_DR and a₀, the NMR spectroscopic and w_TOT values were determined to be too high because of the superposition of the signals coming from dealuminated zeolite framework and silica gel which forms in the zeolite as a result of steaming. The differently determined Si/Al ratios characterise the siliceous extra‐framework species.     

Structural characterization of C-S-H and C-A-S-H samples—Part II: Local environment investigated by spectroscopic analyses

Spectroscopic studies (¹H, ²³Na and ²⁷Al MAS NMR and Raman spectroscopy) have been used to characterize three series of C-S-H samples (0.8<Ca/Si<1.7): one C-S-H series, one aluminum inserted C-S-H series (named C-A-S-H series), and one sodium and aluminum inserted C-S-H series (named C-N-A-S-H series). Previous Rietveld analyses have been performed on the two first series and have clearly shown that (1) a unique ‘tobermorite M defect’ structural model allows to describe the C-S-H structure whatever the Ca/Si ratio and (2) the insertion of aluminum into the C-S-H structure led to the degradation of the crystallinity and to a systematic increase of the basal spacing of about 2 Å regardless the Ca/(Si+Al) ratio (at a constant Al/Si ratio of 0.1). Spectroscopic investigations indicate that the main part of the Al atoms is readily incorporated into the interlayer region of the C-S-H structure. Al atoms are mainly inserted as four-fold coordinated aluminates in the dreierketten silicate chain (either in bridging or paired tetrahedra) at low Ca/Si ratio. Four-fold aluminates are progressively replaced by six-fold coordinated aluminates located into the interlayer region of the C-S-H structure and bonded to silicate chains. Investigation of the hydrogen bonding in C-S-H indicates that the main part of the hydrogen bonds is intra-main layer, and thus explains the low stacking cohesion of the C-S-H structure leading to its nanometric crystal size and the OD character of the tobermorite like structures.     

How Water and Ion Mobility Affect the NMR Fingerprints of the Hydrated JBW Zeolite: A Combined Computational-Experimental Investigation

An important aspect within zeolite synthesis is to make fully tunable framework materials with controlled aluminium distribution. A major challenge in characterising these zeolites at operating conditions is the presence of water. In this work, we investigate the effect of hydration on the ²⁷Al NMR parameters of the ultracrystalline K,Na-compensated aluminosilicate JBW zeolite using experimental and computational techniques. The JBW framework, with Si/Al ratio of 1, is an ideal benchmark system as a stepping stone towards more complicated zeolites. The presence and mobility of water and extraframework species directly affect NMR fingerprints. Excellent agreement between theoretical and experimental spectra is obtained provided dynamic methods are employed with hydrated structural models. This work shows how NMR is instrumental in characterising aluminium distributions in zeolites at operating conditions.     

Structural studies on thorium(IV)-titriplex IV-interacted 13X zeolite

A new zeolite derivative has been prepared by interacting Th(IV) and complexone in HCl medium and neutralising with aqueous ammonia. The amorphous and siliceous derivative showed a total mass loss of 29.25% in TG for stepwise dehydration, dehydroxylation and decomposition. Heats of reaction were 1167.6 J g^–1 at 88.7°C and 75.167 J g^–1 at 492.5°C for loss of volatile components and decomposition respectively.²⁹Si and²⁷Al MAS NMR spectra as well as XRD data of the derivative before and after calcination indicate presence of both four-coordinated and six-coordinated Al in varying ratios and the total loss of crystallinity.The author is grateful to Dr. Alan Dyer of the Department of Chemistry and Applied Chemistry, Salford University and to Dr. Jacek Klinowski of the Department of Chemistry, Cambridge University for providing the thermal data and NMR spectra respectively. He also acknowledges the comments received from Dr. N. Suryaprakash of the Sophisticated Instrument Facility, I.I.Sc., Bangalore on the²⁷Al and²⁹Si spectra of the derivatives.