27Al MAS Research Articles

Coalification and coal alteration under mild thermal conditions

Coalification temperatures are often considered to be approximately 100–170 °C for bituminous coal and 170–275 °C for anthracite. However, our micropetrographic observations, solid state 27Al magic-angle spinning nuclear magnetic resonance measurements, interpretation of δ13C values for whewellite in pelosiderite concretions from Carboniferous sediments, and assessment of whewellite thermal stability show that coalification temperatures can be significantly lower. Also the temperatures of coal alteration may be substantially lower than is stated. Ordinarily, high-temperature alteration is reported, but microthermometric measurements of fluids temperatures and micropetrographic observations show that the coal alteration can take place at low temperatures. For this reason, coals from the Kladno–Rakovník Basin, part of Late Paleozoic continental basins of the Czech Republic, were analyzed. Regarding coalification, micropetrographic characterizations of unaltered coals, the presence of thermally unstable Al complexes in the coal organic mass documented using 27Al MAS NMR method, and proven occurrence of whewellite in pelosiderite concretions suggest a lower coalification temperature, max. ~ 70 °C. Regarding coal alteration, micropetrographic observations revealed (a) the weaker intensity of fluorescence of liptinite, (b) mylonitic structures and microbreccia with carbonate fluid penetration, and (c) high oxygen content in coals (37–38 wt.%). These phenomena are typical for thermal and oxidative alteration of coal. As the temperature of carbonate fluids inferred from fluid inclusion analysis was evaluated as ~ 100–113 °C, the temperature of coal alteration was suggested as ~ 113 °C; the alteration was caused by hot hydrothermal fluids.

Novel ionic liquid-templated ordered mesoporous aluminosilicates: Synthesis, characterization and catalytic properties

Abstract Highly crystalline ordered mesoporous aluminosilicates with hexagonal AlIITM-41 and cubic AlIITM-48 pore symmetries with varying silicon-to-aluminium ratios were hydrothermally synthesized, for the first time, using long-chain ionic-liquid (IL) such as 1-hexadecyl-3-methylimidazolium chloride (HDMIC), as structure directing agent. The prepared materials were systematically characterized by various analytical, spectroscopic and imaging techniques, viz., XRD, BET, TEM and XRF. In addition, the extent of aluminium incorporation and the nature of acid sites were deduced from 27 Al MAS-NMR and NH 3 -TPD measurements. The structural and physico-chemical properties of both AlIITM-41 and AlIITM-48 were compared with analogous AlMCM-41 and AlMCM-48, respectively prepared using hexadecyltrimethylammonium bromide (CTAB). It was found that all the ionic liquid-templated materials, viz., AlIITM-41 and AlIITM-48, and exhibited large surface area, high crystallinity and thicker pore walls. The observed superior orderness of AlIITM-41 and AlIITM-48 could attribute to a well distributed positive charge and π-π stacking of aromatic imidazolium head group of ionic-liquid. In addition, it also assisted in the incorporation of all the aluminium species exclusively in the tetrahedral silicate framework even after the calcination as confirmed by 27 Al MAS NMR. AlIITM-41 and AlIITM-48 possess more medium and strong Bronsted acid sites due to their thicker walls, high crystallinity and presence of tetrahedral aluminium in the framework, due to which they exhibited higher catalytic activity towards tertiary butylation of phenol with a good Para tertiary butyl phenol selectivity compared to commonly used aluminosilicates, H-AlMCM-41 and H-AlMCM-48.

Development and Characterization of Inorganic-Organic (Si-O-Al) Hybrid Geopolymeric Precursors via Solid State Method

In this study, an innovative one part, solution free concept applied for the development of hybrid inorganic–organic geopolymeric precursors having Si-O-Al networks at the precursor stage only. For the process development, fly ash, sodium hydroxide along with rice husk were together mechano-chemically dry grinded for a period of 8, 16 and 24 hours and ‘organic in-organic hybrid geopolymeric precursors’ in solid powder form is obtained. Mechanico-chemically derived tailored organic in-organic hybrid geopolymeric precursors were characterized by different techniques like XRD, 29Si MAS NMR, 27Al MAS NMR, SEM and FESEM. XRD results revealed presence of inorganic phases and organic phase in organic in-organic hybrid geopolymeric precursors. 29Si MAS NMR spectra revealed partial transformation of tertracoordinated Si into pentacoordinated silica due to presence of organic moiety.27Al MAS NMR spectra indicated presence of peaks centered at δ 52 to δ 66 ppm confirmed the formation of geopolymeric precursors. Developed geopolymeric precursor overcome the process drawbacks of conventional geopolymerization process via solution chemistry by making it user friendly as geopolymer from these geopolymeric precursor is obtained by addition of water only unlike conventional geopolymerization process which involves addition of hazardous alkaline solution to aluminosilicate raw material like fly ash. Further, the development of geopolymeric precursor utilize two environmentally unsafe waste materials and resulted in development of material with improved mechanical properties.

Fluorine Modified TAPO-5: Synthesis and Catalytic Performance in Cyclohexanone Ammoximation

A series of fluorine modified TAPO-5 molecular sieves was synthesized by one-pot method using ammo-nium hexafluorotitanate as titanium and fluorine sources. The XPS and DRS UV-Vis results indicated that the exis-tence of F could promote the formation of tetrahedrally coordinated framework Ti and Al, meanwhile, inhibit the formation of anatase TiO2 in TAPO-5 sieves due to the unique role of F in the sol-gel process of metal ions. Further-more, TG, contact angle test, Py-FTIR and 27Al MAS NMR results revealed that fluorine modification increased the surface hydrophobicity and the Lewis acidity of Ti active sites through forming Al x F y units in the neighborhood. All these factors make these fluorine modified TAPO-5 sieves exhibit good catalytic performance in the ammoximation of cyclohexanone.

29Si and 27Al MAS NMR Characterization of the Structural Evolution of a Lateritic Clay under Acidic and Alkaline Treatments

In the present work the modifications induced by the geomimetic processing on the environment of silicon and aluminum atoms are finely characterized by solid state MAS NMR. The raw clay (Lat), a lateritic clay from Yaounde (Cameroon), contains kaolinite, quartz, hematite and goethite as major mineral phases. This material is treated under acidic conditions during 24 h (LatAF) and then under alkaline conditions during 18 days, leading to the final consolidated “geomimetic” product (LatAFCH). The samples have been characterized by 29Si and 27Al solid state NMR at each step of the process.The NMR spectra obtained for the starting clay indicate the presence of AlIV and AlVI populations together with silicon Q2 (0 or 1Al) and Q3 (0 or 1Al) environments located at δiso=-83 ppm and δiso=-91 ppm respectively.The acidic reaction during 24 h, does not significantly affect the silicon-rich layers. It induces a conversion of part of AlIV population into AlVI environment mainly related to the occurrence of six-fold organo-aluminum complexes when using fulvic acid. With inorganic acid, Al dissolution prevails.The neutralization (using lime) of the medium, followed by ageing for 18 days, promotes clay interactions with available calcium ions. The newly formed phases are cementitious CSH, CASH and CAH phases.

The distribution of reactive Ni2+ in 2D Mg2-xNixAl-LDH nanohybrid materials determined by solid state 27Al MAS NMR spectroscopy.

Layered double hydroxides (LDHs), especially (doped) with transition metals, as well as nanohybrid and 2D materials derived from these structures, are interesting materials due to their catalytic and electrochemical properties. Their reactivity is determined by the atomic level distribution of the transition metal in the LDH cation layer, which is essential to control the design of LDHs with optimized properties. However, low crystallinity, absence of long range order, and/or isoelectronic ions often prevent atomic level structural characterization. A series of poorly crystalline Mg2-xNixAl-NO3 LDH materials were investigated by ultrafast 27Al MAS NMR spectroscopy to determine the distribution of Ni2+ in these as well as possible superstructures and their miscibility gaps. Four Ni2Al-LDH samples with interlayer distances ranging from 7.6 to 17.5 Å were prepared to assess the contribution of inter- and intralayer magnetic interactions. The effects of the Ni2+ content and the atomic level distribution of Ni2+ were probed by ultrafast 27Al MAS NMR spectroscopy: the Al distribution can be modeled using a binomial distribution and neither a superstructure was identified for the MgNiAl-LDH sample nor a miscibility gap. The 27Al isotropic shift, δiso(27Al), is a very sensitive probe for a number of neighboring Ni2+ in the first metal ion sphere, but to a smaller degree it is also affected by the intercalated anion (interlayer distance). These results were used for detailed characterization of an exfoliated (2D)-restacked Mg1.83Ni0.17Al-LDH nanohybrid material and a Mg1.83Ni0.17Al-LDH-alginate nanohybrid material, in which 27Al MAS NMR showed how the structure and partial dissolution of the LDHs were retained. In contrast, both powder X-ray diffraction and vibrational spectroscopies (IR and Raman) reflected only the overall change in sample composition.

Tailoring Hierarchical Zeolites with Designed Cationic Surfactants and Their High Catalytic Performance.

Three hierarchical porous zeolites (H-*BEA, H-MTW, and H-*MRE) were successfully synthesized with the assistance of designed cationic surfactants under hydrothermal synthesis conditions. The as-synthesized zeolite samples can be easily regulated by changing the number of long hydrophobic n-alkyl chains. Also, we investigated the relationship between the length of the surfactant and the formation of the microporous structure of the zeolite. Furthermore, the alkylation of benzene with propene was performed as a probe reaction to evaluate the catalytic performance of the synthesized hierarchical zeolites. The resulting materials were characterized by using a complementary combination of techniques, that is, X-ray powder diffraction, N2 adsorption-desorption isotherms, scanning electron microscopy, transmission electron microscopy, Fourier transform IR spectroscopy, 28 Si and 27 Al MAS NMR spectroscopies, thermogravimetric analysis, and computer simulation. These analysis results indicated that quaternary ammonium surfactants acted as organic structure-directing agents (OSDAs) in the formation of these hierarchical zeolite samples, whether the surfactant had long hydrophobic tail groups or not. The simulation results indicated that the organic molecules with no long hydrophobic chain could lead to the synthesis of zeolite through charge control, and the hydrophobic molecules with long hydrophobic chains could form zeolites through orbital control. These hierarchical zeolites showed improved catalytic activity towards the industrially relevant alkylation of benzene with propene compared with conventional zeolites with the same frameworks. More importantly, the success of using quaternary ammonium surfactants with no hydrophobic n-alkyl tail group in the synthesis of hierarchically structured mesoporous zeolites provides a new pathway for the synthesis of hierarchical porous materials by a soft-templating method.

Structural characterization of marine nano-quartz in chalk and flint from North Sea Tertiary chalk reservoirs for oil and gas

A new type of quartz, a nano-quartz consisting of spherical particles, is assumed to have formed by crystallization in the sea during sedimentation of the chalk in the North Sea and to have remained largely intact during burial diagenesis. The presence and nature of this nano-quartz have not been identified until recently, despite the fact that this quartz is the type present in the Upper Cretaceous-Danian chalk reservoir for oil and gas in the North Sea, both in the flint and as dispersed particles. In the present work detailed structural analysis of the nano-quartz has been carried out by X-ray diffraction, solid-state 29 Si and 27 Al MAS NMR, thermal analysis including water release, IR-absorption spectroscopy, and elemental analysis supplemented with analysis of oxygen isotope composition. It is found that IV Al substitutes for Si and that VI Al probably is bonded to hydroxyls on the particle surface of the nano-quartz structures. The charge compensation of tetrahedral Al 3+ , in addition to its conventional way of compensation by formation of the local structural arrangement [AlO 4 /M + ]° defects (M + = H + , Na, K, Li), can occur at the expense of the OH − group coordinating one of the four tetrahedral Si 4+ nearest to the Al 3+ tetrahedron. The most significant feature of the North Sea nano-quartz deduced in the present investigation is the presence of [4H] Si defects, also known as hydrogarnet defects. This defect is present in up to 5% of the tetrahedral sites, whereas Al 3+ occupies less than 1% of the tetrahedral sites. Two types of distribution of the [4H] Si defects were determined. In one of them the [4H] Si defects aggregates parallel to the (0001) plane to form platelets as cracks with hydroxylated surfaces on both sides. The second type of [4H] Si defect occurs in the form of isolated tetrahedral vacant sites.The formation of the aggregated [4H] Si platelets lying in the (0001) plane mostly increases the c parameters of the structure, whereas the isolated [4H] Si defects and K+Na impurities contribute to increasing the a parameters. The remarkable correlation of the positional distribution of the samples revealed from the relationships between a and c parameters and between amount of OH − groups responsible for formation of [4H] Si defects and a and c parameters can be considered as evidence for the validity of the structural formulas and, in general, of the main structural features of the studied samples. The unusually high content of [4H] Si defects in the nano-quartz samples may be related to their formation by precipitation in waters of the Danish North Sea.

Apply 29Si, 27Al MAS NMR and selective dissolution in identifying the reaction degree of alkali activated slag-fly ash composites

Abstract This paper characterizes the phase composition and reaction degree of alkali activated slag, fly ash and their blends by using 29 Si, 27 Al MAS NMR and selective dissolution; with special emphasis on the effect of activator modulus and the usage of blended binders. The results revealed that in alkali activated slag systems, the increase of the activator modulus leads to a reduction of slag reactivity, together with significantly increased Q3(1Al) and reduced Q2(1Al) groups. Selective dissolution contributes to distinguish the unreacted fly ash and reaction products; 29 Si, 27 Al MAS NMR analyses were carried out on both components and their compositions were quantified in detail. Both polymerized Q4 structures and Q3 to Q0 sites were formed, and increasing the activator modulus resulted in an increased content of Q4 groups. When a blended system was applied, the slag reactivity was reduced with the increased fly ash reaction degree, the blended binder exhibited higher contents of newly formed Q4 groups with reduced Si/Al, reduced Q0 sites, shifted mean chain length and Si/Al of the formed C-A-S-H type gels, indicating gel interaction. Applying these two testing methods together brings new insights in understanding the structural composition of alkali activated slag, fly ash and their composites.

Crystal structures of two oxygen-deficient perovskite phases in the CaSiO3–CaAlO2.5 join

The crystal structures of Ca(Al0.5Si0.5)O2.75 and Ca(Al0.4Si0.6)O2.8 ordered oxygen-deficient perovskite phases are synthesized at 7 and 11 GPa, respectively, and 1500 °C, and were studied using NMR and synchrotron powder X-ray diffraction. 29Si MAS NMR, 27Al MAS and 3Q MAS NMR measurements revealed a single tetrahedral Si and single octahedral Al peak for the Ca(Al0.5Si0.5)O2.75 phase, and a tetrahedral and an octahedral Si peak and a single octahedral Al peak for the Ca(Al0.4Si0.6)O2.8 phase. Using this structural information as constraints, the crystal structures were solved from synchrotron X-ray diffraction data by the structure determination from powder diffraction (SDPD) technique. To double-check the structures, first-principles calculations of NMR parameters (chemical shifts and electric field gradients) were also conducted after relaxing the obtained structures. The calculated NMR parameters of both phases are consistent with the observed NMR spectra. The crystal structures of both phases consist of a perovskite-like layer of (Al,Si)O6 octahedra and a double-layer of SiO4 tetrahedra that are stacked alternatively in the [111] direction of ideal cubic perovskite. The perovskite-like layer is made of a double-layer of Al octahedra for the Ca(Al0.5Si0.5)O2.75 phase, and a triple-layer with a Si octahedral layer sandwiched between two Al octahedral layers for the Ca(Al0.4Si0.6)O2.8 phase. A unique feature common to both structures is that each SiO4 tetrahedron has one terminal oxygen that is not shared by other Si or Al. Homologous relation among these phases and merwinite (Ca3MgSi2O8) in terms of different numbers (1–3) of octahedral layers within the perovskite-like layer is noted.

Ethylbenzene disproportionation and p -xylene selectivity enhancement in xylene isomerization using high crystallinity desilicated H-ZSM-5

Abstract Desilication accompanied with minimum loss of crystallinity effect of a high alumina ZSM-5 zeolite on the isomerization reaction of ethylbenzene/xylene mixtures has been considered. Desilication was assessed through XRF, XRD, FTIR, TEM, nitrogen adsorption/desorption, NH 3 -TPD, 29 Si and 27 Al MAS NMR analytical techniques. Desilication was accompanied with the creation of super acid sites. There exists a limit (Si/Al molar ratio of 9.67) for keeping high crystallinity and obtaining improved catalytic performance. Desilication promotes ethylbenzene conversion by disproportionation and trans-alkylation reactions while the same reactions are limited for the xylene isomers. The p -xylene approach to equilibrium improves by more than 7% at 400 °C and a WHSV of 2 h − 1 for the optimum sample with respect to the parent zeolite. At the same conditions, the optimum sample exhibits the maximum ethylbenzene conversion of 89%, i.e. more than 40% w.r.t. of the parent zeolite. However, the xylene yield decreases only 3%.

Solid-state MAS NMR investigations for pentavalent cation-replaced pollucite compounds with a negative thermal expansion coefficient

Pollucite compounds with an aluminosilicate structure, V-replaced pollucite, Cs0.7V0.1Al0.8Si2.1O6 (CVAS), P-replaced pollucite, Cs0.7P0.1Al0.8Si2.1O6 (CPAS), and Nb-replaced pollucite, Cs0.7Nb0.1Al0.8Si2.1O6 (CNbAS), were synthesized by a multistep heat treatment of 550–1200 °C. CVAS exhibited the superior thermal expansion with thermal expansion coefficients of 0.9 × 10−6 °C−1 (30–500 °C), −0.9 × 10−6 °C−1 (30–150 °C), and −0.4 × 10−6 °C−1 (30–100 °C). Solid-state 29Si MAS NMR spectroscopy clarified that the number of Si–O–Si bonds of tetrahedra in the framework of CVAS was larger than those of CPAS and CNbAS. The chemical shift for peaks of the 29Si MAS NMR spectrum of CVAS was larger than those of CPAS and CNbAS, suggesting that the bond angle of tetrahedra was enlarged by the V replacement. Solid-state 27Al MAS NMR spectroscopy implied that CVAS had a small amount of sixfold coordinated Al species, which resulted in an increase in the number of Si–O–Si bonds of tetrahedra of CVAS.

Crystal structure, thermal decomposition mechanism and catalytic performance of hexaaquaaluminum methanesulfonate

Hexaaquaaluminum methanesulfonate crystals, [Al(H2O)6][CH3SO3]3 were synthesized by a hydrothermal reaction of Al(OH)3 with methanesulfonic acid. Single-crystal diffraction determination revealed that Al3+ was coordinated by six water molecules in octahedral geometry, while the CH3SO3– anion connected with Al3+ through coordinated water molecules by hydrogen bonds. The six-coordinate environment of Al was also determined by 27Al MAS NMR measurement. Thermogravimetric analysis and Fourier transform infrared spectroscopy showed that the decomposition intermediate at 265–365 °C was Al2(μ-OH)(CH3SO3)5 and the final product was amorphous Al2O3 residue with about 0.8 wt% SO3 at 520–800 °C. A pure phase of [Al(H2O)6][CH3SO3]3 was confirmed by powder X-ray diffraction analysis. Esterification of n-butyric acid with n-butanol and ketalization of cyclohexanone with glycol catalyzed by [Al(H2O)6][CH3SO3]3 and Al2(μ-OH)(CH3SO3)5, respectively, proceeded in 100% yield by continuously removing the produced water. In the case of tetrahydropyranylation of n-butanol at room temperature in dichloromethane, the catalytic activity of [Al(H2O)6][CH3SO3]3 was much lower than that of Al2(μ-OH)(CH3SO3)5. Furthermore, both [Al(H2O)6][CH3SO3]3 precursor and Al2(μ-OH)(CH3SO3)5 catalysts could be recycled.

Resolution of the Two Aluminum Sites in Ettringite by 27Al MAS and MQMAS NMR at Very High Magnetic Field (22.3 T)

Ettringite (Ca6[Al(OH)6]2(SO4)3·26H2O) is the first hydration product formed during Portland cement hydration. 27Al MAS NMR has been used in a wide number of studies to detect and quantify ettringite in hydrated cement blends by the observation of a single, narrow resonance at 13–14 ppm. This work reports the first observation of resonances from two distinct Al sites in octahedral coordination for ettringite, employing 27Al MAS and MQMAS NMR at an ultrahigh magnetic field (22.3 T). Thereby, the 27Al NMR spectra are in agreement with the most accepted trigonal model for the ettringite structure. 27Al quadrupole coupling parameters and isotropic chemical shifts for the two Al sites are determined from simulations and least-squares optimization of slow-speed 27Al MAS NMR spectra of the satellite transitions. These data reveal that the local environments for the two octahedral Al sites are very similar, in accord with the most recent XRD refinements of the ettringite structure. Finally, the significant improv...

Structural analysis of mesoporous vermiculite modified with lanthanum

Clays have demonstrated an important role in many industrial processes and its modification have been a promising line of research, such as its intercalation and pillaring. The synthesis of vermiculite modified with aluminum and aluminum-lanthanum has great relevance, since the materials obtained can be used in separation processes by adsorption and catalysis. For characterization of the crystallographic phases of the synthesized materials were obtained diffraction patterns (XRD) that confirmed the effectiveness of the methodology used, and to evaluate the morphology were carried out nitrogen adsorption analysis (BET), where the results confirmed the mesoporosity of the synthesized materials. 27Al MAS NMR spectrometry was applied to distinguish between tetrahedrally coordinated aluminum and octahedrally coordinated.

Characterization of Al30 in commercial poly-aluminum chlorohydrate by solid-state 27Al NMR spectroscopy

Investigation of commercially produced hydrolysis salts of aluminum by solid-state 27Al NMR spectroscopy and size-exclusion chromatography (SEC) reveals well-defined and distinct Al environments that can be related to physicochemical properties. 27Al MAS and MQ-MAS NMR spectroscopic data show that the local structure of the solids is dominated by moieties that closely resemble the Al30 polyoxocation (Al30O8(OH)56(H2O)2618+), accounting for 72–85% of the total Al. These Al30-like clusters elute as several size fractions by SEC. Comparison of the SEC and NMR results indicates that the Al30-like clusters includes intact isolated clusters, moieties of larger polymers or aggregates, and possibly fragments resembling δ-Al13 Keggin clusters. The coagulation efficacy of the solids appears to correlate best with the abundance of intact Al30-like clusters and of smaller species available to promote condensation reactions.

Aluminum environments in synthetic Ca-Tschermak clinopyroxene (CaAlAlSiO6) from Rietveld refinement,27Al NMR, and first-principles calculations

27 Al magic-angle spinning nuclear magnetic resonance (MAS NMR) and 27 Al triple quantum (3Q) MAS NMR spectroscopy have been performed at 21.1 Tesla (T), as a direct probe of environment around Al in synthetic Ca-Tschermak’s clinopyroxene, CaAlAlSiO 6 , henceforward referred to as CaTs. For comparison, 27 Al MAS NMR of CaTs has also been performed at 14.1 T. The 27 Al 3QMAS NMR spectrum of CaTs has revealed various local environments around octahedral and tetrahedral Al, both ordered and disordered, symmetrical, and distorted. Rietveld refinement of powder X-ray diffraction data has confirmed the high-temperature, long-range disordered C 2/ c structure for this sample. The 27 Al MAS NMR spectra of CaTs look broadly similar at 14.1 and 21.1 T. Both spectra exhibit two distinct peaks at the octahedral site and an irregularly shaped, broad tetrahedral site. The line widths are significantly broader at lower field and the 27 Al 3QMAS NMR spectrum at 21.1 T exhibits several additional peaks. At least three peaks were resolved at the octahedral site (in both the MAS spectrum along F2 and the 3Q spectrum along F1), whereas two peaks are clearly resolved at the tetrahedral site at 21.1 T. One tetrahedral peak, observed at both fields, is broad in F1 and narrow in F2, spread along the isotropic shift diagonal, indicating a highly disordered but relatively symmetric environment. The second peak, newly observed at 21.1 T, is narrow in F1 but very broad in F2, indicating an ordered but highly distorted environment. This peak has not been observed at lower magnetic field strengths. Octahedral peak assignments have been made according to the number of Al atoms in the six tetrahedral sites around M1, where an increasing number of NNN tetrahedral Al (2Al, 3Al, and 4Al) is correlated with displacement of the chemical shift to higher frequency. Assigned sites are similar to the local tetrahedral environments around M1 in ordered P 2 1 / n or C 2 structures, suggesting the presence of ordered domains in this otherwise disordered C 2/ c structure. To aid in the interpretation of these tetrahedral Al environments, density functional theory (DFT) calculations have been performed using two approximations of the CaTs crystal structure: fully ordered tetrahedral chains or fully disordered tetrahedral chains. These calculations suggest that the tetrahedral Al site is a sensitive indicator of order-disorder in CaTs. Tetrahedral Al sites in ordered tetrahedral chains (Si-O-Al-O-Si…) are predicted to have only large C Q , whereas tetrahedral Al sites in disordered systems (Al-O-Al-O-Al…) are predicted to have only small C Q . Both environments appear to exist in the synthetic CaTs sample in this study. Cation order-disorder has implications for thermobarometry based on CaTs-containing pyroxenes. The discovery of the new highly distorted tetrahedral site at ultrahigh magnetic field suggests that highly distorted Al sites in silicate minerals may be NMR-invisible in 27 Al 3QMAS NMR spectra acquired at lower fields, and these will have been systematically overlooked. This underscores the necessity to collect 27 Al NMR spectra of silicates at the highest available magnetic field strength.

An investigation of local Fe2 + order-disorder in a mantle grospydite garnet using paramagnetically shifted 27Al and 29Si MAS NMR resonances

An attempt is made for the first time to measure the local (short-range) distribution of the X-cations in a ternary almandine-pyrope-grossular garnet solid solution using paramagnetically shifted NMR resonances. Initial 27 Al MAS NMR measurements made on an almandine-rich garnet of composition Alm 45 Prp 42 Grs 13 proved to be uninterpretable because of the high Fe 2+ concentration. Thus, a grossular-rich and almandine-poorer garnet occurring in a mantle grospydite xenolith taken from the Roberts Victor kimberlite, South Africa, was chosen for detailed 27 Al and 29 Si MAS NMR spectroscopic study. The crystals are compositionally homogeneous based on electron microprobe analysis, showing no measurable zoning, and have the formula Alm 23 Prp 30 Grs 47 [(Fe 0.23 Mg 0.30 Ca 0.47 ) 3 Al 2 Si 3 O 12 ]. The garnet is cubic with the conventional space group Ia 3 d . The composition and, also importantly, the lack of measurable zoning or compositional heterogeneity, as well as the mode of occurrence, make this garnet a key sample for investigating the possible presence of short-range X cation order. The 27 Al MAS NMR spectrum shows a very broad asymmetric resonance located between about 100 and −50 ppm. It consists of a number of individual closely overlapping paramagnetically shifted resonances, which are difficult to analyze quantitatively. The 29 Si MAS NMR spectrum, showing better resolution, has two broad but observable resonances termed S0 and S4. S0 is located between about −60 ppm and −160 ppm and S4 is centered at roughly 95 ppm. Both S0 and S4 are composite resonances containing many overlapping individual peaks. S0 contains information on local X-cation configurations, where an isolated SiO 4 group in the garnet structure does not have any edge-shared Fe 2+ -containing dodecahedra. S4 involves various local configurations where there is one edge-shared dodecahedron containing Fe 2+ . The measured intensity of the resonances S0 and S4 are roughly similar to calculated intensities assuming random Fe 2+ -cation mixing. These first results do not indicate any overt short-range X-cation order in grospydite garnet.

Nuclear Magnetic Resonance to investigate inorganic porous materials of interest in the cultural heritage field

Nuclear Magnetic Resonance (NMR) can be successfully applied to a wide number of organic, inorganic, and hybrid materials regarding cultural heritage. High-resolution solid-state NMR provides information on the structure of materials, and portable NMR devices allow non-destructive and non-invasive in situ investigation of variably sized objects. This result is possible by combining open magnets and surface radiofrequency coils to generate a sensitive volume external to the sensor and inside the object under investigation. In this paper we focus on the application of NMR to investigate inorganic porous materials such as pottery, plasters, and stones from cultural heritage sites. 27 Al MAS and 3QMAS, and 29 Si MAS high-resolution solid-state NMR along with spectral deconvolution allowed for the investigation of the chemical structure of ancient pottery. Portable unilateral NMR was used to investigate, in a non-invasive and non-destructive way, the porous structure of pottery. The effect of protective-consolidating treatments on plaster was carefully investigated by 1 H NMR depth profiles that allowed for scanning with micrometric resolution of plaster specimens. Changes occurring in the total open porosity after treatments were also evaluated. NMR diffusion measurements provided information on the restricted geometry of the porous structure of two types of biocalcarenite and tuff. A suitable processing of collected data enabled us to define the average pore radius and pores’ interconnection in these materials.

Development of the CON-type Aluminosilicate Zeolite and Its Catalytic Application for the MTO Reaction

The CON-type aluminosilicate zeolites, which consist of a three-dimensional pore system with 12-, 12-, and 10-membered ring pores have been prepared by postsynthesis and the newly developed direct-synthesis methods. We first found that the CON-type aluminosilicate zeolites exhibited a higher catalytic performance in the methanol to olefins (MTO) reaction in terms of duration and propene selectivity than the MFI and *BEA-type aluminosilicate zeolites. They exhibited high propene selectivity, low ethene selectivity, and a very long catalytic life compared to Beta and ZSM-5; the selectivity for C3–C4 olefins reached 80%. Interestingly, the CON-type aluminosilicate zeolite synthesized by the direct-synthesis method showed a much longer catalytic lifetime than the one obtained by the postsynthesis method. The 27Al MAS and 27Al MQMAS NMR spectra suggest that there is a significant difference in the state of tetrahedrally coordinated Al species between the directly and postsynthesized zeolites, leading to the ma...