D. A. Matthijs de Winter

Morphology-dependent zeolite intergrowth structures leading to distinct internal and outer-surface molecular diffusion barriers

Zeolites play a crucial part in acid-base heterogeneous catalysis. Fundamental insight into their internal architecture is of great importance for understanding their structure-function relationships. Here, we report on a new approach correlating confocal fluorescence microscopy with focused ion beam-electron backscatter diffraction, transmission electron microscopy lamelling and diffraction, atomic force microscopy and X-ray photoelectron spectroscopy to study a wide range of coffin-shaped MFI-type zeolite crystals differing in their morphology and chemical composition. This powerful combination demonstrates a unified view on the morphology-dependent MFI-type intergrowth structures and provides evidence for the presence and nature of internal and outer-surface barriers for molecular diffusion. It has been found that internal-surface barriers originate not only from a 90 degrees mismatch in structure and pore alignment but also from small angle differences of 0.5 degrees-2 degrees for particular crystal morphologies. Furthermore, outer-surface barriers seem to be composed of a silicalite outer crust with a thickness varying from 10 to 200 nm.

Tomography of insulating biological and geological materials using focused ion beam (FIB) sectioning and low‐kV BSE imaging

Tomography in a focused ion beam (FIB) scanning electron microscope (SEM) is a powerful method for the characterization of three‐dimensional micro‐ and nanostructures. Although this technique can be routinely applied to conducting materials, FIB–SEM tomography of many insulators, including biological, geological and ceramic samples, is often more difficult because of charging effects that disturb the serial sectioning using the ion beam or the imaging using the electron beam. Here, we show that automatic tomography of biological and geological samples can be achieved by serial sectioning with a focused ion beam and block‐face imaging using low‐kV backscattered electrons. In addition, a new ion milling geometry is used that reduces the effects of intensity gradients that are inherent in conventional geometry used for FIB–SEM tomography.

Superplastic nanofibrous slip zones control seismogenic fault friction

Understanding the internal mechanisms controlling fault friction is crucial for understanding seismogenic slip on active faults. Displacement in such fault zones is frequently localized on highly reflective (mirrorlike) slip surfaces, coated with thin films of nanogranular fault rock. We show that mirror-slip surfaces developed in experimentally simulated calcite faults consist of aligned nanogranular chains or fibers that are ductile at room conditions. These microstructures and associated frictional data suggest a fault-slip mechanism resembling classical Ashby-Verrall superplasticity, capable of producing unstable fault slip. Diffusive mass transfer in nanocrystalline calcite gouge is shown to be fast enough for this mechanism to control seismogenesis in limestone terrains. With nanogranular fault surfaces becoming increasingly recognized in crustal faults, the proposed mechanism may be generally relevant to crustal seismogenesis. Nanogranular microstructures found in simulated carbonate faults control the physical sliding mechanism during rupture. Nanofibers involved in fault rupture Changing fault properties during rupture dictates the size and extent of an earthquake. Faulting leads to well-known microstructures that may play a role in how natural faults slip during rupture. Verberne et al. investigated tiny, nanogranular fibers found in microstructures generated on simulated carbonate faults. A microphysical model was able to account for how the small and aligned fiber produced runaway fault slip, similar to that seen in natural faults. These small structures play a role in carbonate faulting and similar microstructures could control fault rupture in other types of rocks. Science, this issue p. 1342

The Porosity, Acidity, and Reactivity of Dealuminated Zeolite ZSM-5 at the Single Particle Level: The Influence of the Zeolite Architecture

A combination of atomic force microscopy (AFM), high-resolution scanning electron microscopy (HR-SEM), focused-ion-beam scanning electron microscopy (FIB-SEM), X-ray photoelectron spectroscopy (XPS), confocal fluorescence microscopy (CFM), and UV/Vis and synchrotron-based IR microspectroscopy was used to investigate the dealumination processes of zeolite ZSM-5 at the individual crystal level. It was shown that steaming has a significant impact on the porosity, acidity, and reactivity of the zeolite materials. The catalytic performance, tested by the styrene oligomerization and methanol-to-olefin reactions, led to the conclusion that mild steaming conditions resulted in greatly enhanced acidity and reactivity of dealuminated zeolite ZSM-5. Interestingly, only residual surface mesoporosity was generated in the mildly steamed ZSM-5 zeolite, leading to rapid crystal coloration and coking upon catalytic testing and indicating an enhanced deactivation of the zeolites. In contrast, harsh steaming conditions generated 5-50 nm mesopores, extensively improving the accessibility of the zeolites. However, severe dealumination decreased the strength of the Brønsted acid sites, causing a depletion of the overall acidity, which resulted in a major drop in catalytic activity.

The making of frozen-hydrated, vitreous lamellas from cells for cryo-electron microscopy

There has been a long standing desire to produce thick (up to 500 nm) cryo-sections of fully hydrated cells and tissue for high-resolution analysis in their natural state by cryo-transmission electron microscopy. Here, we present a method that can successfully produce sections (lamellas in FIB-SEM terminology) of fully hydrated, unstained cells from high-pressure frozen samples by focused ion beam (FIB) milling. The samples are therefore placed in thin copper tubes and vitrified by high-pressure freezing. For transfer, handling and subsequent milling, the tubes are placed in a novel connective device (ferrule) that protects the sample from devitrification and contamination and passes through all operation steps. A piezo driven sample positioning stage (cryo-nano-bench, CNB) with three degrees of freedom was additionally developed to enable accurate milling of frozen-hydrated lamellas. With the CNB, high-pressure frozen samples can be milled to produce either thin lamellas (<100 nm), for direct imaging by high-resolution cryo-TEM or thicker lamellas (300-500 nm) for cryo-electron tomography. The sample remains vitreous throughout the process by using the presented tools and methods. The results are an important step towards investigating larger cells and even tissue in there natural state which in the end will enable us to gain better insights into cellular processes.

Intergrowth Structure of Zeolite Crystals and Pore Orientation of Individual Subunits Revealed by Electron Backscatter Diffraction/Focused Ion Beam Experiments

Zeolites are of tremendous scientific and technological importance, since a number of processes in modern chemical industry, such as crude oil refining, rely on their unique combination of catalytic activity and shape selectivity.[1–3] Consequently, significant efforts have been directed at obtaining in-depth insight into the molecular processes taking place within zeolite pores during catalysis.[4–6] A popular strategy is to investigate large zeolite crystallites, which are well-defined, ordered, and reproducible and can be used as model systems for diffusion and catalysis studies.[7–15] However, this taskis complicated by the complex structure of zeolite crystals comprising several intergrown building blocks. The interfaces of these subunits may constitute diffusion boundaries due to potential mismatch in the alignment of the microporous network,[16] and this can render certain regions of the zeolite crystals inaccessible for reactant molecules and consequently affect the catalytic activity of the material.[8, 10, 17]

Nanocrystalline slip zones in calcite fault gouge show intense crystallographic preferred orientation: Crystal plasticity at sub-seismic slip rates at 18–150 °C

A central aim in fault mechanics is to understand the microphysical mechanisms controlling aseismic-seismic transitions in fault gouges, and to identify microstructural indicators for such transitions. We present new data on the slip stability of calcite fault gouges, and on microstructural development down to the nanometer scale. Our experiments consisted of direct shear tests performed dry at slip rates of 0.1–10 μm/s, at a constant normal stress of 50 MPa, at 18–150 °C. The results show a transition from stable to (potentially) unstable slip above ~80 °C. All samples recovered showed an optical microstructure characterized by narrow, 30–40-μm-wide, Riedel and boundary shear bands marked by extreme grain comminution, and a crystallographic preferred orientation (CPO). Boundary shear bands, sectioned using FIB-SEM (focused ion beam scanning electron microscopy), revealed angular grain fragments decreasing from 10 to 20 μm at the outer margins to ~0.3 μm in the shear band core, where dense aggregates of nanograins also occurred. Transmission electron microscopy, applied to foils extracted from boundary shears using FIB-SEM, combined with the optical CPO, showed that these aggregates consist of calcite nanocrystals, 5–20 nm in size, with the (104)[201] dislocation glide system oriented parallel to the shear plane and direction. Our results suggest that the mechanisms controlling slip include cataclasis and localized crystal plasticity. Because crystal plasticity is strongly thermally activated, we infer that the transition to velocity-weakening slip is likely due to enhanced crystal plasticity at >80 °C. This implies that tectonically active limestone terrains will tend to be particularly prone to shallow-focus seismicity.

NanoSelect Pd Catalysts: What Causes the High Selectivity of These Supported Colloidal Catalysts in Alkyne Semi‐Hydrogenation?

In recent years, many articles describing the preparation of supported colloidal catalysts have been published. The semi‐hydrogenation of alkynes to yield cis‐alkenes is often used as a test reaction in these publications. Many highly selective catalysts are described. However, a satisfactory explanation for the high reported selectivity has never been shown. Here we report a study on the possible effects that lead to the large selectivity differences between current commercial Pd/C catalysts and our newly developed NanoSelect catalysts. The focus is on differences in chemical composition as well as catalyst characteristics. We use a focused ion beam scanning electron microscope (FIB‐SEM) to locate the metal particle with respect to the surface of the support. FIB‐SEM analysis clearly shows the absence of the active component inside the support material, which could explain the high observed selectivity. Nevertheless, an effect of the stabilizer cannot be ruled out.

Architecture-Dependent Distribution of Mesopores in Steamed Zeolite Crystals as Visualized by FIB-SEM Tomography†

Break on through: Steaming-induced mesopores of individual ZSM-5 crystals were studied by a combination of focused ion beam (FIB) and scanning electron microscopy (SEM) tomography (see picture). In this manner, quantitative insight into the width, length, morphology, and distribution of mesopores generated within zeolite crystals has been obtained. Keywords:crystal intergrowth;scanning probe microscopy;mesoporosity;tomography;zeolites

Coke Formation in a Zeolite Crystal During the Methanol-to- Hydrocarbons Reaction as Studied with Atom Probe Tomography

Abstract Understanding the formation of carbon deposits in zeolites is vital to developing new, superior materials for various applications, including oil and gas conversion processes. Herein, atom probe tomography (APT) has been used to spatially resolve the 3D compositional changes at the sub‐nm length scale in a single zeolite ZSM‐5 crystal, which has been partially deactivated by the methanol‐to‐hydrocarbons reaction using 13C‐labeled methanol. The results reveal the formation of coke in agglomerates that span length scales from tens of nanometers to atomic clusters with a median size of 30–60 13C atoms. These clusters correlate with local increases in Brønsted acid site density, demonstrating that the formation of the first deactivating coke precursor molecules occurs in nanoscopic regions enriched in aluminum. This nanoscale correlation underscores the importance of carefully engineering materials to suppress detrimental coke formation.