Luc Delmotte

Synthesis and characterization of cloverite: a novel gallophosphate molecular sieve with three-dimensional 20-membered ring channels

Abstract Cloverite, a novel cubic microporous gallophosphate, with three-dimensional channels circumscribed by 20-membered rings in the shape of a four-leafed clover, was synthesized in the presence of fluoride ions and quinuclidine. It is stable to at least 500°C in a dry atmosphere and shows high adsorption capacity for n -hexane, xylene, and mesitylene. By 13 C n.m.r., it was found that quinuclidine is protonated, thus compensating the negative charge of fluoride located in the double four-rings. The 31 P and 71 Ga MAS n.m.r. results are in agreement with the crystal structure analysis.

Influence of synthesis conditions and postsynthesis treatments on the nature and quantity of structural defects in highly siliceous MFI zeolites: A high-resolution solid-state 29Si n.m.r. study

The formation and annealing of various kinds of defects in the framework of highly siliceous MFI-type zeolites, as evidenced by high-resolution solid-state 29 Si n.m.r., can be explained by considering the systematic influence of synthesis parameters and postsynthesis treatments. High pH values and high concentrations of alkali metal and fluoride ions prevent a complete polycondensation of the silicate species and generate materials that contain significant levels of nonbonding point defects. By contrast, a high crystallization temperature results in the ready hydrolysis of the terminal Si-O − groups, leading to structures containing fewer defects. A large number of T vacancies (hydroxyl nests) are created in zeolites crystallized at low temperatures in the presence of high Pr 4 N + concentations and in the absence of F − or Na + ions. Such conditions favor the formation of double-5-ring silicate anions. The hypothesis, that such species may further condense, conducting to frameworks with an important number of empty T-sites, is proposed. On the basis of these findings, ideal synthesis conditions can be proposed to produce (Si) MFI zeolites that contain a minimum number of defects. Various postsynthesis treatments, namely, different calcination conditions followed, or preceded, by selected ionic (akali cation) exchanges, result in a partial or a nearly total healing of these defects in the final materials.

27Al MAS NMR characterization of AlPO4-14 enhanced resolution and information by MQMAS Dr. Hellmut G. Karge on the occasion of his 65th birthday

Abstract The crystalline microporous aluminophosphate AlPO4-14 was studied using 27Al NMR spectroscopy, with both conventional MAS and two-dimensional multiple-quantum MAS (MQMAS) techniques. Data obtained for the four non-equivalent framework aluminum atoms detected in AlPO4-14 are reported. They are found to occur with the ratio 1:1:1:1 according to the proposed crystal structure. The aim of this paper is also to compare the NMR methods used in this work with those found in literature. It is concluded that the new MQMAS method is by now the best approach to distinguish easily the non-equivalent Al atoms in the structure of such materials. It is also very efficient to obtain rapidly the necessary information about distribution of chemical shifts and quadrupolar interactions.

19F MAS n.m.r. studies of crystalline microporous solids synthesized in the fluoride medium

Abstract Highly siliceous TON-, MTT-, and MFI-type zeolites, alumino-, gallo-, titano-, and germanosilicates of MFI-type structure, and aluminophosphates and silicoaluminophosphates of AFI-, AEL-, FAU-, and CHA-type structure, containing various alkylammonium species R + , and synthesized in fluoride medium, were studied by 19 F MAS n.m.r. The as-synthesized samples, with a fluorine weight content up to 1.7% were characterized by a single main peak attributed to fluorine anions balancing the charge of the organic cation. The variations of chemical shifts with the nature of the templates were very small. The values ranged from −64 to −75 ppm in silicates and from −119 to −123 ppm in aluminophosphates. After calcination in dry gas, the remaining fluorine (0.1-0.3%) is bonded to Si (peak close to −155 ppm) or to T III elements (peak close to −140 ppm). When the samples were heated in moist atmosphere, no trace of F was found.

High-resolution solid-state 29Si and 13C n.m.r. on highly siliceous MFI-type zeolites synthesized in nonalkaline fluoride medium

Abstract Highly resolved 29 Si and 13 MAS -n.m.r. spectra of pure silica zeolites of the MFI-type synthesized according to a new route reveal new features, which are indicative of the very low defect content and the very high crystallinity of these materials.

High resolution solid-state n.m.r. investigation of the filler-rubber interaction: 1. High speed 1H magic-angle spinning n.m.r. spectroscopy in carbon black filled styrene-butadiene rubber

Abstract This present work, dealing with filler/rubber interactions, provides a new approach for investigating the behaviour of elastomeric chains (styrene-butadiene rubber, SBR) in the close vicinity of carbon black surfaces. Pulsed nuclear magnetic resonance measurements have been carried out on pure SBR, and on carbon gels obtained by solvent extraction of the carbon black filled elastomers. The initial concentration of carbon black in the filler/rubber mixtures was varied between 20 and 100 parts per hundred parts by weight (phr). The high resolution proton spin-spin relaxation time, T 2 , has been measured for each of the individual resonance species belonging to the SBR chain. High resolution was achieved by rapidly spinning the sample at the magic angle. It has been observed that a very high magic-angle spinning (MAS) rate (> 18 kHz) is necessary to achieve a fully resolved spectrum of SBR. However, at a spinning rate of ∼ 15 kHz it is possible to avoid all of the spinning side bands and to deconvolute, unambiguously, the different resonance peaks that are present in the spectrum. In the unfilled elastomer, at temperatures much higher than the T g , the chain segmental motions are anisotropic and deviate from true liquid-like behaviour. The adsorbed rubber chains are found to consist of loosely and tightly immobilized segments. The relative immobilization of the different protons has evidenced the methine 1 H to be much more immobilized than the aromatic or methylene species. Therefore, the olefinic part of the butadiene segment of the elastomeric chain appears to be the most affected by the carbon black surface. Moreover, T 2 is found to be independent of the filler concentration in the 30–80 phr range, and the relative concentration of the tightly bound rubber in the composite shows a maximum at a filler content of ∼ 50 phr, where maximum reinforcement is normally observed. As far as the molecular dynamics is concerned, highly filled systems (> 80 phr carbon black) behave differently from low and medium filled systems (

19 F MAS-NMR study of structural fluorine in some natural and synthetic 2:1 layer silicates

High-resolution solid-state, fluorine-19, magic-angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR) was used to study natural and synthetic fluorinated 2:1 layer silicates of known composition. This technique enabled us to determine directly the coordination of structural fluorine and it was found to be sensitive to both the chemical nature of the octahedral elements (Al, Mg, Li) and the type of octahedral sheet (di- or trioctahedral). The observed chemical shifts at −132, −152, −176 and −182 ppm (relative to CFC13) were assigned to different environments of fluorine. The results were then used to characterize synthetic 2:1 layer silicates with unknown octahedral composition.

19F/29Si distance determination in fluoride-containing octadecasil by Hartmann–Hahn cross-polarization under fast magic-angle spinning

19F/29Si Hartmann-Hahn continuous wave cross-polarization (CP) has been applied under fast magic-angle spinning (MAS) to a powder sample of octadecasil. Strong oscillations occur during CP on a sideband matching condition between the isolated 29Si-19F spin pairs formed by the silicons in the D4R units and the fluoride anions. The magnitude of the dipolar coupling constant was deduced directly from the line-splitting between the intense singularities of the Pake-like patterns obtained by Fourier transformation of the oscillatory polarization transfer. The corresponding Si-F internuclear distance, r = 2.62 +/- 0.05 A, is found to be in very good agreement with the X-ray crystal structure and the value of 2.69 +/- 0.04 A recently reported from rotational echo double resonance (REDOR) and transferred echo double resonance (TEDOR) nuclear magnetic resonance (NMR) experiments. Furthermore, the CP technique is still reliable under fast MAS where both REDOR and TEDOR sequences suffer from severe artefacts due to finite pulse lengths. In octadecasil, a spinning frequency of approximately 14 kHz is shown to be necessary for an effective suppression of 19F-19F spin diffusion. The influences of experimental missettings and radiofrequency (RF) field inhomogeneity are taken into account.

Fast crystallization of alumino- and silicoaluminophosphates with a VFI framework topology

Abstract A fast crystallization method for VPI-5-like products is reported. The method allows, for the first time, the full crystallization in less than 1 h of pure aluminophosphates and silicoaluminophosphates. This method requires a high rate of temperature increase of the hydrogel. Products are characterized by X-ray diffraction patterns, scanning electron microscopy, electronic microprobe analysis, 27Al MAS n.m.r., 29Si MAS n.m.r., and 31P MAS and CPMAS n.m.r.. N.m.r. spectra are unique and this is due to the high crystallinity of the products. These spectra are compared to the literature and are briefly commented on.

High resolution solid state 2D NMR analysis of biomass and biochar.

Solid state NMR methods are required to analyze biomass as a function of its chemical or biological treatment for biofuels, chemicals, or biochar production. The native polymers network in lignocellulosic biomass and other solid materials, such as coal, coke, or biochar, can hardly be analyzed by liquid state NMR due to their poor swelling ability without chemical modification. A (1)H-(13)C two-dimensional heteronuclear correlation (HETCOR) experiment with frequency-switched Lee-Goldburg (FSLG) irradiation is performed on a high field spectrometer (750 MHz). This method leads to previously unattained resolution for biomass and biochar and offers a unique ability to reveal their chemical composition. The formation of aromatic moieties from carbohydrates and lignin thermal conversion is clearly distinguished. This method can be applied to all other carbonaceous materials.