Charakterisierung ungeordneter Strukturen anhand von partiellen Strukturfaktoren aus Elementverteilungsbildern

In dieser Arbeit wird eine Methode zur Bestimmung von partiellen Zwei-Teilchen-Strukturfaktoren aus Elementverteilungsbildern am Beispiel der spinodalen Entmischung einer Eisen-Chrom-Legierung vorgestellt. Hierbei wird auf die unterschiedlichen experimentellen Einflüsse durch die energiefilternde Elektronenmikroskopie eingegangen. Insbesondere das Slowscan CCD-Kamerasystem zeichnet sich durch unterschiedliches Verhalten je nach Beleuchtungsintensität aus. Mit dieser Methode lassen sich dann elementaufgelöst die partiellen Zwei-Teilchen-Strukturfaktoren bestimmen. Mit diesen erhält man dann zu Kleinwinkelstreuexperimenten vergleichbare Daten, die nur mit sehr hohem Aufwand elementaufgelöste Daten erlauben. Als Ergänzung hierzu werden die Ergebnisse von Simulationen ungeordneter Strukturen gezeigt. Insgesamt zeigt sich eine hohe Vergleichbarkeit der experimentellen Ergebnisse, so dass diese Methode als wertvolle Ergänzung zu bestehenden Methoden betrachtet werden kann.In this work a method to calculate partial two-particle-structure-factors from energy filtered elemental maps is presented using the example of spinodal decomposition of an alloy consisting of iron and chromium. Special care has to be taken to describe the behavior of a slow-scan CCD camera depending on the illumination intensity during image acquisition.Considering these artifacts, the modulation transfer function of the camera and the inelastic transfer function of specimen and microscope it is then possible to calculate the partial two-particle-structure-factors with elemental sensitivity. The resulting data set is comparable to small angle scattering experiments where considerable effort has to be afforded to achieve elemental sensitivity. Additionally the results of simulated disordered structures are presented to verify the comparability of the presented structure factors with those of small angle. The method presented here is a valuable addition to existing methods measuring partial two-particle- structure-factors

Dissolution and precipitation of copper-rich phases during heating and cooling of precipitation-hardening steel X5CrNiCuNb16-4 (17-4 PH)

Continuous heating transformation (CHT) diagrams and continuous cooling transformation (CCT) diagrams of precipitation-hardening steels have the drawback that important information on the dissolution and precipitation of Cu-rich phases during continuous heating and cooling are missing. This work uses a comparison of different techniques, namely dilatometry and differential scanning calorimetry for the in situ analysis of the so far neglected dissolution and precipitation of Cu-rich phases during continuous heating and cooling to overcome these drawbacks. Compared to dilatometry, DSC is much more sensitive to phase transformation affecting small volume fractions, like precipitation. Thus, the important solvus temperature for the dissolution of Cu-rich phases was revealed from DSC and integrated into the CHT diagram. Moreover, DSC reveals that during continuous cooling from solution treatment, premature Cu-rich phases may form depending on cooling rate. Those quench-induced precipitates were analysed for a broad range of cooling rates and imaged for microstructural analysis using optical microscopy, scanning electron microscopy and transmission electron microscopy. This information substantially improves the CCT diagram

Cascade Synthesis of Pyrroles from Nitroarenes with Benign Reductants Using a Heterogeneous Cobalt Catalyst

A bifunctional 3d-metal catalyst for the cascade synthesis of diverse pyrroles from nitroarenes is presented. The optimal catalytic system Co/NGr-C@SiO2-L is obtained by pyrolysis of a cobalt-impregnated composite followed by subsequent selective leaching. In the presence of this material, (transfer) hydrogenation of easily available nitroarenes and subsequent Paal–Knorr/Clauson-Kass condensation provides >40 pyrroles in good to high yields using dihydrogen, formic acid, or a CO/H2O mixture (WGSR conditions) as reductant. In addition to the favorable step economy, this straightforward domino process does not require any solvents or external co-catalysts. The general synthetic utility of this methodology was demonstrated on a variety of functionalized substrates including the preparation of biologically active and pharmaceutically relevant compounds, for example, (+)-Isamoltane. © 2020 The Authors. Published by Wiley-VCH Gmb

Supported CuII Single-Ion Catalyst for Total Carbon Utilization of C2 and C3 Biomass-Based Platform Molecules in the N-Formylation of Amines

The shift from fossil carbon sources to renewable ones is vital for developing sustainable chemical processes to produce valuable chemicals. In this work, value-added formamides were synthesized in good yields by the reaction of amines with C2 and C3 biomass-based platform molecules such as glycolic acid, 1,3-dihydroxyacetone and glyceraldehyde. These feedstocks were selectively converted by catalysts based on Cu-containing zeolite 5A through the in situ formation of carbonyl-containing intermediates. To the best of our knowledge, this is the first example in which all the carbon atoms in biomass-based feedstocks could be amidated to produce formamide. Combined catalyst characterization results revealed preferably single CuII sites on the surface of Cu/5A, some of which form small clusters, but without direct linking via oxygen bridges. By combining the results of electron paramagnetic resonance (EPR) spin-trapping, operando attenuated total reflection (ATR) IR spectroscopy and control experiments, it was found that the formation of formamides might involve a HCOOH-like intermediate and .NHPh radicals, in which the selective formation of .OOH radicals might play a key role. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH Gmb

Hydrogenation of terminal and internal olefins using a biowaste-derived heterogeneous cobalt catalyst

Hydrogenation of olefins is achieved using biowaste-derived cobalt chitosan catalysts. Characterization of the optimal Co@Chitosan-700 by STEM (scanning transmission electron microscopy), EELS (electron energy loss spectroscopy), PXRD (powder x-ray diffraction), and elemental analysis revealed the formation of a distinctive magnetic composite material with high metallic Co content. The general performance of this catalyst is demonstrated in the hydrogenation of 50 olefins including terminal, internal, and functionalized derivatives, as well as renew-ables. Using this nonnoble metal composite, hydrogenation of terminal C==C double bonds occurs under very mild and benign conditions (water or methanol, 40° to 60°C). The utility of Co@Chitosan-700 is showcased for efficient hydrogenation of the industrially relevant examples diisobutene, fatty acids, and their triglycerides. Because of the magnetic behavior of this material and water as solvent, product separation and recycling of the catalyst are straightforward

Understanding the Performance and Stability of Supported Ni-Co-Based Catalysts in Phenol HDO

Performances of bimetallic catalysts (Ni-Co) supported on different acidic carriers (HZSM-5, HBeta, HY, ZrO2) and corresponding monometallic Ni catalysts in aqueous phase hydrodeoxygenation of phenol were compared in batch and continuous flow modes. The results revealed that the support acidity plays an important role in deoxygenation as it mainly controls the oxygen-removing steps in the reaction network. At the same time, sufficient hydrothermal stability of a solid catalyst is essential. Batch experiments revealed 10Ni10Co/HZSM-5 to be the best-performing catalyst in terms of conversion and cyclohexane yield. Complementary continuous runs provided more insights into the relationship between catalyst structure, efficiency and stability. After 24 h on-stream, the catalyst still reveals 100% conversion and a slight loss (from 100% to 90%) in liquid hydrocarbon selectivity. The observed alloy of Co with Ni increased dispersion and stability of Ni-active sites, and combination with HZSM-5 resulted in a well-balanced ratio of metal and acid sites which promoted all necessary steps in preferred pathways. This was proved by studies of fresh and spent catalysts using various characterization techniques (N2 physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and infrared spectroscopy of adsorbed pyridine (pyr-IR))

Synthesis of Single Atom Based Heterogeneous Platinum Catalysts: High Selectivity and Activity for Hydrosilylation Reactions

Catalytic hydrosilylation represents a straightforward and atom-efficient methodology for the creation of C-Si bonds. In general, the application of homogeneous platinum complexes prevails in industry and academia. Herein, we describe the first heterogeneous single atom catalysts (SACs), which are conveniently prepared by decorating alumina nanorods with platinum atoms. The resulting stable material efficiently catalyzes hydrosilylation of industrially relevant olefins with high TON (≈105). A variety of substrates is selectively hydrosilylated including compounds with sensitive reducible and other functional groups (N, B, F, Cl). The single atom based catalyst shows significantly higher activity compared to related Pt nanoparticles

Development of Highly Stable Low Ni Content Catalyst for Dry Reforming of CH4-Rich Feedstocks

Highly active and coking-resistant Ni catalysts suited for the dry reforming of CH4-rich gases (70 vol %, e. g. biogas or sour natural gas) were prepared starting from a Mg-rich Mg−Al hydrotalcite support precursor. Calcination at 1000 °C yields two phases, MgO and MgAl2O4 spinel. Complexation-deposition of Ni with citric acid on the preformed support as well as lanthanum addition yields a catalyst with remarkably low carbon accumulation over 100 h on stream attributed to both high Ni dispersion and preferred interactions of Ni with MgO on MgAl2O4. © 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Chemical in‐depth analysis of (Ca/Sr)F2 core–shell like nanoparticles by X‐ray photoelectron spectroscopy with tunable excitation energy

The fluorolytic sol–gel synthesis is applied with the intention to obtain two different types of core–shell nanoparticles, namely, SrF2–CaF2 and CaF2–SrF2. In two separate fluorination steps for core and shell formation, the corresponding metal lactates are reacted with anhydrous HF in ethylene glycol. Scanning transmission electron microscopy (STEM) and dynamic light scattering (DLS) confirm the formation of particles with mean dimensions between 6.4 and 11.5 nm. The overall chemical composition of the particles during the different reaction steps is monitored by quantitative Al Kα excitation X-ray photoelectron spectroscopy (XPS). Here, the formation of stoichiometric metal fluorides (MF2) is confirmed, both for the core and the final core–shell particles. Furthermore, an in-depth analysis by synchrotron radiation XPS (SR-XPS) with tunable excitation energy is performed to confirm the core–shell character of the nanoparticles. Additionally, Ca2p/Sr3d XPS intensity ratio in-depth profiles are simulated using the software Simulation of Electron Spectra for Surface Analysis (SESSA). In principle, core–shell like particle morphologies are formed but without a sharp interface between calcium and strontium containing phases. Surprisingly, the in-depth chemical distribution of the two types of nanoparticles is equal within the error of the experiment. Both comprise a SrF2-rich core domain and CaF2-rich shell domain with an intermixing zone between them. Consequently, the internal morphology of the final nanoparticles seems to be independent from the synthesis chronology.European Metrology Programme for Innovation and Research (EMPIR) http://dx.doi.org/10.13039/100014132Peer Reviewe

Chemical in-depth analysis of (Ca/Sr)F2 core–shell like nanoparticles by X-ray photoelectron spectroscopy with tunable excitation energy

The fluorolytic sol–gel synthesis is applied with the intention to obtain two different types of core–shell nanoparticles, namely, SrF2–CaF2 and CaF2–SrF2. In two separate fluorination steps for core and shell formation, the corresponding metal lactates are reacted with anhydrous HF in ethylene glycol. Scanning transmission electron microscopy (STEM) and dynamic light scattering (DLS) confirm the formation of particles with mean dimensions between 6.4 and 11.5 nm. The overall chemical composition of the particles during the different reaction steps is monitored by quantitative Al Kα excitation X-ray photoelectron spectroscopy (XPS). Here, the formation of stoichiometric metal fluorides (MF2) is confirmed, both for the core and the final core–shell particles. Furthermore, an in-depth analysis by synchrotron radiation XPS (SR-XPS) with tunable excitation energy is performed to confirm the core–shell character of the nanoparticles. Additionally, Ca2p/Sr3d XPS intensity ratio in-depth profiles are simulated using the software Simulation of Electron Spectra for Surface Analysis (SESSA). In principle, core–shell like particle morphologies are formed but without a sharp interface between calcium and strontium containing phases. Surprisingly, the in-depth chemical distribution of the two types of nanoparticles is equal within the error of the experiment. Both comprise a SrF2-rich core domain and CaF2-rich shell domain with an intermixing zone between them. Consequently, the internal morphology of the final nanoparticles seems to be independent from the synthesis chronology