Chemists of all fields currently publish about 50 000 crystal structures per year, the vast majority of which are X‐ray structures. We determined two molecular structures by employing electron rather ...than X‐ray diffraction. For this purpose, an EIGER hybrid pixel detector was fitted to a transmission electron microscope, yielding an electron diffractometer. The structure of a new methylene blue derivative was determined at 0.9 Å resolution from a crystal smaller than 1×2 μm2. Several thousand active pharmaceutical ingredients (APIs) are only available as submicrocrystalline powders. To illustrate the potential of electron crystallography for the pharmaceutical industry, we also determined the structure of an API from its pill. We demonstrate that electron crystallography complements X‐ray crystallography and is the technique of choice for all unsolved cases in which submicrometer‐sized crystals were the limiting factor.
Electrons instead of X‐rays: An electron diffractometer was tailored and employed for de novo structure determination from submicrometer‐sized crystals. A new methylene blue derivative was analysed together with a microcrystalline extract of an active pharmaceutical ingredient from a pill. The results obtained on submicrometer‐sized samples complement X‐ray crystallography.
Unveiling the coke formation in zeolites is an essential prerequisite for tackling the deactivation of these catalysts in the transformations of hydrocarbons. Herein, we present the direct mapping of ...coke in the micropores of ZSM‐5 catalysts used in methanol‐to‐hydrocarbons conversion by single‐crystal electron diffraction analysis. The latter technique revealed a polycyclic aromatic structure along the straight channel, wherein the high‐quality data permit refinement of its occupancy to about 40 %. These findings were exploited to analyze the evolution of micropore coke during the reaction. Herein, coke‐associated signals, which correlate with the activity loss, indicate that the nucleation of coke commences in the intersections of sinusoidal and straight channels, while the formation of coke in the straight pores occurs in the late stages of deactivation. The findings uncover an attractive method for analyzing coke deposition in the micropore domain.
Electron diffraction was demonstrated here as a powerful tool to localize coke in the micropore domain of the ZSM‐5 catalyst that is deactivated in methanol‐to‐hydrocarbon conversion. The results show that the formation of coke is initiated in the channel intersections, while its deposition in the straight pores occurs in the late deactivation stages.
3D electron crystallography has recently attracted much attention due to its complementarity to X-ray crystallography in determining the structure of compounds from submicrometre sized crystals. A ...big obstacle lies in obtaining complete data, required for accurate structure determination. Many crystals have a preferred orientation on conventional, flat sample supports. This systematically shades some part of the sample and prevents the collection of complete data, even when several data sets are combined. We introduce two types of three-dimensional sample supports that enable the collection of complete data sets. In the first approach the carbon layer forms coils on the sample support. The second approach is based on chaotic nylon fibres. Both types of grids disrupt the preferred orientation as we demonstrate with a well suited crystal type of MFI-type zeolites. The easy-to-obtain three-dimensional sample supports have different features, ensuring a broad spectrum of applications for these 3D support grids.
Acid or base leaching are well‐established tools in the synthesis of mesoporous zeolites. Previous studies suggest an inherent link between the structure‐property relationship of mesoporous zeolites, ...that is, chemical resistance, pore diameter and distribution, with zeolite synthesis or crystallization conditions. The exact nature and/or origin of this link is currently however, poorly established. Here, we provide evidence how zeolite crystallization conditions influence the leaching behavior and thus structure of mesoporous zeolites. Electron microscopy and in situ small angle X‐ray scattering both confirmed the crystallization of ZSM‐5 to utilize both nanoparticles and oligomers as elemental building blocks. Utilization of these species is highly depended on supersaturation. The precursor solution of decreased water content favored a faster consumption of nanoparticles compared to its oligomers at the early stage of crystallization. Then the addition of oligomers can heal the surface imperfections and thus the resulting zeolite showed a higher resistance against acid leaching. In contrast, within the precursor solution of increased water content the slower consumption of nanoparticles led to crystals with a less robust rim. Defects existed in the rim due to limited healing by oligomers and, as such, mesopores can be created by the following post‐treatment. Precise control over selected crystallization conditions can therefore further aid the design of optimized mesoporous zeolites.
Crystal growth and crystal leaching: The crystal growth of ZSM‐5 zeolites depend on the consumption of nanoparticles and oligomers. The variation in the consumption rates of each species leads to crystals with different properties, which can be reflected by crystal leaching. Hollow zeolites with microporous or mesoporous shells can be produced by optimizing the synthesis and post‐synthetic conditions.
In this study, the synergistic behavior of Ni species and bimodal mesoporous undoped SnO2 is investigated in oxygen evolution reactions (OERs) under alkaline conditions without any other modification ...of the compositional phases or using noble metals. An efficient and environmentally friendly hydrothermal method to prepare bimodal mesoporous undoped SnO2 with a very high surface area (>130 m2 g–1) and a general deposition–precipitation method for the synthesis of well-dispersed Ni species on undoped SnO2 are reported. The powders were characterized by adsorption–desorption isotherms, TG-DTA, XRD, SEM, TEM, Raman, TPR-H2, and XPS. The best NiSn composite generates, under certain experimental conditions, a very high TOF value of 1.14 s–1 and a mass activity higher than 370 A g–1, which are remarkable results considering the low amount of Ni deposited on the electrode (3.78 ng). Moreover, in 1 M NaOH electrolyte, this material produces more than 24 mA cm–2 at an overpotential value of approximately +0.33 V, with only 5 wt % Ni species. This performance stems from the dual role of undoped SnO2, on the one hand, as a support for active and well-dispersed Ni species and on the other hand as an active player through the oxygen vacancies generated upon Ni deposition.
The simple perrhenate salt N(hexyl)
4
(ReO
4
) acts as a catalyst for the reduction of organic carbonyls and carbon dioxide by primary and secondary hydrosilanes. In the case of CO
2
, this results ...in the formation of methanol equivalents
via
silylformate and silylacetal intermediates. Furthermore, the addition of alkylamines to the reaction mixture favours catalytic amine
N
-methylation over methanol production under certain conditions. DFT analysis of the mechanism of CO
2
reduction shows that the perrhenate anion activates the silylhydride forming a hypervalent silicate transition state such that the CO
2
can directly cleave a Si–H bond.
3D electron diffraction has reached a stage where the structures of chemical compounds can be solved productively. Instrumentation is lagging behind this development, and to date dedicated electron ...diffractometers for data collection based on the rotation method do not exist. Current studies use transmission electron microscopes as a workaround. These are optimized for imaging, which is not optimal for diffraction studies. The beam intensity is very high, it is difficult to create parallel beam illumination and the detectors used for imaging are of only limited use for diffraction studies. In this work, the combination of an EIGER hybrid pixel detector with a transmission electron microscope to construct a productive electron diffractometer is described. The construction not only refers to the combination of hardware but also to the calibration of the system, so that it provides rapid access to the experimental parameters that are necessary for processing diffraction data. Until fully integrated electron diffractometers become available, this describes a setup for productive and efficient operation in chemical crystallography.
Installation of the EIGER X 1M detector onto an electron microscope and system calibration for data collection turns a transmission electron microscope into an electron diffraction instrument. Data can be collected and processed with a throughput that meets the requirements of a modern X‐ray facility. The setup described here offers access to single‐crystal structure determination from microcrystalline powder when large single crystals cannot be produced.
The crystal structure of a chemical compound serves several purposes: its coordinates represent three-dimensional information about the connectivity between the atoms; it is the only technique that ...determines the absolute configuration of chiral molecules; it enables determining structure–function relations; and crystallographic data at atomic resolution distinguish between element types and serve as a confirmation of synthesis protocols. Here, we collected electron diffraction data from albite and from a Linde Type A (LTA) type zeolite. Both compounds are aluminosilicates with well-defined silicon and aluminum crystallographic sites. Data were recorded with the “adJUstiNg Gain detector FoR the Aramis User station” (JUNGFRAU detector) and we made use of its capability of energy discrimination to suppress noise. For both compounds, crystallographic refinement distinguishes correctly between silicon and aluminum, even though these elements have very similar electron scattering factors. These results highlight the quality of the electron diffraction data and the reliability of the models for chemical interpretation. Further development in this direction will provide enormous opportunities for structure–function studies by diffraction.
Heterogeneity of nano-sized zeolite crystals Wennmacher, Julian T.C.; Li, Teng; Zaubitzer, Christian ...
Microporous and mesoporous materials,
03/2020, Volume:
294
Journal Article
Peer reviewed
Open access
Analytical characterization and evaluation of performance of zeolite catalysts are normally done under the assumption of a homogeneous batch. However, it is known that in the same batch particles of ...the zeolite ZSM-5 can be very different one from another, regarding their aluminum content and catalytic performance. Here, we quantify the extent of this heterogeneity within a singular synthesis batch of nanocrystalline ZSM-5, through the analysis of single crystalline individua. We found that the overall aluminum content was distributed unequally between two kinds of crystal populations. Cornered crystals contained three times more aluminum than round-shaped crystals. This observation connects morphological differences to the chemical composition of each zeolite crystal for the first time. This finding could provide a means for performance optimization in zeolite synthesis.
Display omitted
•A singular synthesis batch of nano-ZSM-5 crystals can yield very different crystals.•The aluminium content of some crystalline individua was up to threefold higher than the overall determined aluminium content.•Morphology was linked to chemical composition: Cornered crystals contained more aluminium than round-shaped crystals.
In this study, the synergistic behavior of Ni species and bimodal mesoporous undoped SnO
is investigated in oxygen evolution reactions (OERs) under alkaline conditions without any other modification ...of the compositional phases or using noble metals. An efficient and environmentally friendly hydrothermal method to prepare bimodal mesoporous undoped SnO
with a very high surface area (>130 m
g
) and a general deposition-precipitation method for the synthesis of well-dispersed Ni species on undoped SnO
are reported. The powders were characterized by adsorption-desorption isotherms, TG-DTA, XRD, SEM, TEM, Raman, TPR-H
, and XPS. The best NiSn composite generates, under certain experimental conditions, a very high TOF value of 1.14 s
and a mass activity higher than 370 A g
, which are remarkable results considering the low amount of Ni deposited on the electrode (3.78 ng). Moreover, in 1 M NaOH electrolyte, this material produces more than 24 mA cm
at an overpotential value of approximately +0.33 V, with only 5 wt % Ni species. This performance stems from the dual role of undoped SnO
, on the one hand, as a support for active and well-dispersed Ni species and on the other hand as an active player through the oxygen vacancies generated upon Ni deposition.
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