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A screening study of the catalytic performance of ternary alloy nanoparticles containing nickel, iron and gallium supported on silica for methanol synthesis from CO2 and H2 was performed. Catalysts were prepared by incipient wetness impregnation and subsequently reduced in H2 before catalytic testing. Ni2FeGa showed the best performance of the tested catalysts in terms of methanol yield. An optimization of the preparation was done to improve activity and selectivity, reaching performance close to that of prepared commercially available Cu/ZnO/Al2O3/MgO at low reaction temperatures and pressure. Extensive in situ characterisation using environmental TEM, in situ XRD and in situ EXAFS of the formation of the Ni2FeGa catalyst explains an optimal reduction temperature of 550°C: warm enough that the three atomic species will form an alloy while cold enough to prevent the catalyst from sintering during the formation.

The coupled effects of pH and ionic strength impact a variety of geochemical processes in the subsurface. In this study, we investigate the interactions of H+ and major ions at the surface-solution interface of silica porous media under advection-dominated flow-through conditions. A series of 21 column experiments were performed by systematically injecting solutions of different pH and ionic strengths. Three types of porous media (i.e., two natural sands and quartz beads) were considered in order to explore differences in surface/solution interactions among quartz materials. Multiple lines of evidence were used to characterize the geochemical processes taking place during the flow-through experiments: (i) breakthrough curves of pH and major ions were measured at the column outlets; (ii) the natural sand surfaces were characterized by chemical extractions and scanning electron microscopy and the quartz structure was analyzed by XRD; (iii) reactive transport modeling was performed to quantitatively interpret the experimental results. We observed strong reactivity of the quartz surface characterized by significant release of protons when interacting with the major ions. The results also show significant differences in the quantity of protons emitted from the surfaces of the three silica porous media, as well as in the shape of the pH breakthrough curves. Reactive transport modeling was based on a multicomponent ionic transport formulation and on surface complexation description of the solid/solution interactions. The surface complexation model included the individual contributions of quartz and Fe/Al oxides present in the sand coatings with the component additive approach. For each medium, a single set of surface complexation parameters capable of reproducing the experimental dataset (i.e., 7 columns) was calibrated by parallelizing the simulations of the flow-through experiments. This approach allowed us to capture the pH and ionic species behavior within a large range of ionic strengths (i.e., [0–100] mM). The SCMs quantitatively show that H+ is released from quartz upon adsorption of Na+ and that the protonation of the oxides surfaces retards the pH front. Differences in acidity behavior between the silica surfaces seem to be primarily controlled by differences in surface topology, crystal structure of quartz and/or various presence of aluminosilicates. This study demonstrates that the reactivity and diversity of quartz surfaces in silica porous media and the complex interplay with oxide surfaces in the coatings control the transport of aqueous charged species in flow-through systems.

Designing stable materials for processes operating under harsh reaction conditions, like CO hydrogenation, is a challenging topic in catalysis. These may provoke several deactivation mechanisms simultaneously, like thermal sintering, oxidation or poisoning of the active sites. We report HZSM‐5 supported cobalt catalysts, exhibiting cobalt nanoparticles encapsulated inside, or located at the exterior of the ZSM‐5 support. The materials were studied by a combination of ex situ and in situ electron microscopy with respect to the growth of the cobalt particles. After 1200 h time on stream under CO hydrogenation conditions, the spent catalyst showed minimal sintering of encapsulated cobalt particles. In situ environmental TEM experiments under model reduction and CO hydrogenation conditions indicate the presence of cobalt nanoparticles, which appear highly resistant towards sintering even up to 700 °C. These results provide a first indication for the preparation of sinter stable catalysts suitable for operating in harsh reaction environments.

A common expectation in heterogeneous catalysis is that the optimal activity will occur for the particle size with the highest concentration of undercoordinated step, edge, or corner sites, expectedly in the 2-oxygenates, to illuminate the origin of this effect. Studying Rh/SiO2 catalysts, we show that smaller (2-oxygenate formation and is the reason for the high selectivity of rhodium to such complex products, which is at its highest for the smallest (∼2 nm) investigated particles.

Lignosulfonate was subjected to a reductive catalytic degradation in ethanol medium at 310 °C in the presence of alumina supported NiMo catalysts and H2. The liquid and solid products were analyzed with size exclusion chromatography (SEC), gas chromatography mass spectrometry (GC–MS), two-dimensional gas chromatography (GC × GC), heteronuclear single quantum coherence nuclear magnetic resonance (HSQC NMR) and elemental analysis. The highest oil yield and the lowest char yield obtained was 88 and 15 wt %, respectively. The liquefied species were mainly dimers and oligomers with minor yields of monomers. The catalyst was important for stabilization of reactive intermediates either by hydrogenation or coupling with ethanol. Simultaneous deoxygenation and desulfurization reactions took place in the presence of the catalyst; the oxygen and sulfur content in the oil fraction obtained after 4 h reaction time were 11.2 and 0.1 wt %, indicating considerable deoxygenation and desulfurization compared to the lignosulfonate feedstock (O, 30.8 wt %; S, 3.1 wt %). The effect of the reaction parameters such as temperature, reaction time and catalyst mass was studied. It was observed that by increasing the temperature from 260 to 310 °C the degradation increased, however, the SEC analysis showed that the degradation progressed only to a certain size range dimers to oligomers in the reaction temperatures studied. Investigating the effect of reaction time of 1, 2, 3, and 4 h indicated that degradation, deoxygenation, desulfurization and alkylation reactions progressed over time. The reusability of the catalyst without any pretreatment was confirmed by an almost constant oil yield in three repeated experiments with the same catalyst batch. The results show that alumina supported NiMo catalysts are very promising catalysts for conversion of lignosulfonate to liquid products.

The carbon formation causing deactivation during CO methanation was studied for a Ni/Al2O3 catalyst. Sulfur-free methanation at low temperature (573 K) for various lengths of time was followed by temperature-programmed hydrogenation (TPH) providing information on carbon types involved in the deactivation of the catalyst. Three main carbon hydrogenation peaks were evident from TPHs following methanation: ∼460, ∼650, and ∼775 K. It is suggested that the ∼460 K TPH peak was composed of two peaks: a surface carbide peak at 445–460 K, and a peak due to carbon dissolved into the nickel at 485 K based on CO and CH4 adsorption measurements and XRD analysis. The 650 and 775 K temperature peaks are assigned to polymerized carbon structures and the ∼775 K peak was found to be the primary cause of deactivation as judged by a linear correlation between its amount and the degree of catalyst deactivation. The longer the duration of the methanation test, the more carbon was built up on the Ni surfaces and the highest obs...

In recent years, X-ray ptychography has been established as a valuable tool for high-resolution imaging. Nevertheless, the spatial resolution and sensitivity in coherent diffraction imaging are limited by the signal that is detected over noise and over background scattering. Especially, coherent imaging of weakly scattering specimens suffers from incoherent background that is generated by the interaction of the central beam with matter along its propagation path in particular close to and inside of the detector. Common countermeasures entail evacuated flight tubes or detector-side beamstops, which improve the experimental setup in terms of background reduction or better coverage of high dynamic range in the diffraction patterns. Here, we discuss an alternative approach: we combine two ptychographic scans with and without beamstop and reconstruct them simultaneously taking advantage of the complementary information contained in the two scans. We experimentally demonstrate the potential of this scheme for hard X-ray ptychography by imaging a weakly scattering object composed of catalytic nanoparticles and provide the analysis of the signal-to-background ratio in the diffraction patterns.

The activation of iron oxide Fischer–Tropsch Synthesis (FTS) catalysts was investigated during pretreatment: reduction in hydrogen followed by carburization in either CO or syngas mixture, or simultaneously reduction and carburization in syngas. A combination of different complementary in situ techniques was used to gain insight into the behavior of Fe-based FTS catalysts during activation. In situ XRD was used to identify the crystalline structures present during both reduction in hydrogen and carburization. An increase in reduction rate was established when increasing the temperature. A complete reduction was demonstrated in the ETEM and a grain size dependency was proven, i.e. bigger grains need higher temperature in order to reduce. XPS and XAS both indicate the formation of a small amount of carbonaceous species at the surface of the bulk metallic iron during carburization.

The stability of Ni-MoS2/ZrO2 toward water, potassium, and chlorine containing compounds during hydrodeoxygenation (HDO) of a mixture of phenol and 1-octanol was investigated in a high pressure gas and liquid continuous flow fixed bed setup at 280 °C and 100 bar. To maintain the stability of the catalyst, sufficient co-feeding of a sulfur source was necessary to avoid oxidation of the sulfide phase by oxygen replacement of the edge sulfur atoms in the MoS2 structure. However, the addition of sulfur to the feed gas resulted in the formation of sulfur containing compounds, mainly thiols, in the oil product if the residence time was too low. At a weight hourly space velocity (WHSV) of 4.9 h−1 the sulfur content in the liquid product was 980 ppm by weight, but this could be decreased to 5 ppm at a WHSV of 1.4 h−1. A high co-feed of sulfur was needed when water was present in the feed and the H2O/H2S molar ratio should be below ca. 10 to maintain a decent stability of the catalyst. Chlorine containing compounds caused a reversible deactivation of the catalyst when co-fed to the reactor, where the catalytic activity could be completely regained when removing it from the feed. Commonly, chlorine, H2O, and H2S all inhibited the activity of the catalyst by competing for the active sites, with chlorine being by far the strongest inhibitor and H2S and H2O of roughly the same strength. Dissimilar, potassium was a severe poison and irreversibly deactivated the catalyst to 2 slabs.

Infrared spectroscopy on CO chemisorbed on Raney Cu and materials with Cu dispersed as nanoparticles on oxide supports was used to evaluate support effects on the Cu surface properties. The C-O frequency (νC-O) is sensitive to the charge on the adsorption site with νC-O being high on Cu+, intermediate on Cu0, and low on Cu−, whereby this method can probe the charging state of the Cu surface. The Raney Cu reference demonstrates the complex analysis of the IR band intensity, which can be susceptible to dipole coupling. This means that the most intense IR bands may be higher frequency bands strengthened by such coupling effects rather than the bands arising from the most abundant sites. The νC-O of the major band attributable to CO adsorbed on the metallic surface follows the order: Cu/SiO2 > Raney Cu > Cu/Al2O3 > Cu/TiO2. Given the charge-frequency relationship these support-dependent frequency shifts are attributed to changes in the charging of the Cu surface caused by support effects. The Cu surface is more electron deficient for Cu/SiO2 and electron enriched for Cu/TiO2. For the Cu/ZnO(/Al2O3) samples, which are important as industrial methanol synthesis catalysts, band assignments are complicated by a low νC-O on Cu+ sites connected to the ZnO matrix. However, Cu/ZnO(/Al2O3) has a spectral feature at 2065-68 cm−1, which is a lower frequency than observed in the Cu single crystal studies in the literature and thus indicative of a negative charging of the Cu surface in such systems. Experiments with co-adsorption of CO and electron-withdrawing formate on Cu/ZnO and Cu/SiO2 show that νC-O in the adsorbed CO shifts upwards with increasing HCOO coverage. This illustrates that the surface charge is donated to the electron-withdrawing formate adsorbate, and as a result co-adsorbed CO experiences a more charge depleted Cu surface that yields higher νC-O. The support-dependent surface charging may thus affect the interaction with adsorbates on the metal surface and thereby impact the catalytic properties of the Cu surface. Dilution of the samples in KBr, which has been used in many studies in the literature, had pronounced effects on the spectra. The presence of KBr leads to an increase in νC-O indicative of an electron depleted surface attributed to transfer of electron-withdrawing bromine species from KBr to the sample.

Catalytic upgrading of pyrolysis vapors from wheat straw over Na2CO3 impregnated γ-Al2O3 was studied as a promising route to biofuels. The Na species were homogenously distributed on the support and created a basicity of ~0.02 mmol CO2/g catalyst, at 80% lower catalyst acidity. Analytical pyrolysis using a micro-pyrolyzer showed that Na-Al2O3 particularly decreased the yield of acids via ketonization, which was confirmed by feeding carboxylic acid model compounds. The presence of Na decreased the coke yield and catalyzed the coke combustion, decreasing the combustion temperature by ~100 °C.Subsequently, 100 g Na-Al2O3 catalyst was tested in an ablative bench scale fast pyrolysis unit where ~5 kg of wheat straw was pyrolyzed and the vapors passed the catalytic reactor during six reaction/regeneration cycles. In agreement with the micro-pyrolyzer results, Na-Al2O3 was highly effective in reducing the acidity of the bio-oils. Total acid numbers (TAN) as low as ~1–4 mg KOH/g could be maintained up to high B:C ratios of ~13. For a given TAN, this allowed operating to higher B:C ratios and provided higher oil yields compared to using acidic catalysts such as γ-Al2O3 and HZSM-5 zeolite for vapor treatment. At bio-oil energy recoveries of ~60–70% relative to raw bio-oil, the deoxygenation was comparable to the acidic catalysts. Operation to higher B:C ratios allowed increasing the energy recovery to ~85% relative to the non-treated bio-oil while still obtaining a good deoxygenation performance of ~60%. Despite the hydrothermal conditions during reaction and oxidative regeneration, the activity of Na-Al2O3 was regained by coke combustion, the Na remained well dispersed on the support, and the catalyst maintained its capacity for CO2 adsorption at 500 °C after six reaction/regeneration cycles.

The CO2 hydrogenation to methanol is efficiently catalyzed at ambient pressure by nanodispersed intermetallic GaPd2/SiO2 catalysts prepared by incipient wetness impregnation. Here we optimize the catalyst in terms of metal content and reduction temperature in relation to its catalytic activity. We find that the intrinsic activity is higher for the GaPd2/SiO2 catalyst with a metal loading of 13 wt.% compared to catalysts with 23 wt.% and 7 wt.%, indicating that there is an optimum particle size for the reaction of around 8 nm. The highest catalytic activity is measured on catalysts reduced at 550 °C. To unravel the formation of the active phase, we studied calcined GaPd2/SiO2 catalysts with 23 wt.% and 13 wt.% using a combination of in situ techniques: X-ray diffraction (XRD), X-ray absorption near edge fine structure (XANES) and extended X-ray absorption fine structure (EXAFS). We find that the catalyst with higher metal content reduces to metallic Pd in a mixture of H2/Ar at room temperature, while the catalyst with lower metal content retains a mixture of PdO and Pd up to 140 °C. Both catalysts form the GaPd2 phase above 300 °C, albeit the fraction of crystalline intermediate Pd nanoparticles of the catalyst with higher metal loading reduces at higher temperature. In the final state, the catalyst with higher metal loading contains a fraction of unalloyed metallic Pd, while the catalyst with lower metal loading is phase pure. We discuss the alloying mechanism leading to the catalyst active phase formation selecting three temperatures: 25 °C, 320 °C and 550 °C.

A nanodispersed intermetallic GaPd2/SiO2 catalyst is prepared by simple impregnation of industrially relevant high-surface-area SiO2 with Pd and Ga nitrates, followed by drying, calcination, and reduction in hydrogen. The catalyst is tested for CO2 hydrogenation to methanol at ambient pressure, revealing that the intrinsic activity of the GaPd2/SiO2 is higher than that of the conventional Cu/ZnO/Al2O3, while the production of the undesired CO is lower. A combination of complementary in situ and ex situ techniques are used to investigate the GaPd2/SiO2 catalyst. In situ X-ray diffraction and in situ extended X-ray absorption fine structure spectroscopy show that the GaPd2 intermetallic phase is formed upon activation of the catalyst via reduction and remains stable during CO2 hydrogenation. Identical location–transmission electron microscopy images acquired ex situ (i.e., micrographs of exactly the same catalyst area recorded at the different steps of activation and reaction procedure) show that nanopartic...

Transmission Kikuchi diffraction (TKD) facilitates automated orientation mapping of thin films in scanning electron microscopes (SEM). In this study TKD is applied for the first time to perform in-situ annealing experiments on gold thin films deposited on a MEMS-based heating system. The very local heating associated with this system enables reliable TKD measurements at elevated temperatures without notable disturbance from infrared radiation. The dewetting of an Au thin film into Au nanoparticles upon heating is followed with orientation mapping in a temperature range between 20 °C and 900 °C. The local thickness variation associated with the dewetting is observed qualitatively by observing the intensity of the transmitted beam, which decreases as the film thickness increases locally. The results of this study reveal that TKD is a well suited technique to study thin-film stability and solid state dewetting. Moreover, the outcome of this methodological study provides a baseline for further in-situ crystallographic studies of electron transparent samples in the SEM.

NiFeOxHy are the most active catalysts for oxygen evolution in a base. For this reason, they are used widely in alkaline electrolysers. Several open questions remain as to the reason for their exceptionally high catalytic activity. Here we use a model system of mass-selected NiFe nanoparticles and isotope labelling experiments to show that oxygen evolution in 1 M KOH does not proceed via lattice exchange. We complement our activity measurements with electrochemistry–mass spectrometry, taken under operando conditions, and transmission electron microscopy and low-energy ion-scattering spectroscopy, taken ex situ. Together with the trends in particle size, the isotope results indicate that oxygen evolution is limited to the near-surface region. Using the surface area of the particles, we determined that the turnover frequency was 6.2 ± 1.6 s−1 at an overpotential of 0.3 V, which is, to the best of our knowledge, the highest reported for oxygen evolution in alkaline solution. The reason for the high water-oxidation activity of Ni(Fe)OxHy catalysts in alkaline electrolyte is not yet well understood. Now, Chorkendorff and co-workers report that oxygen evolution is limited to the near-surface region by measuring the activity trends of mass-selected NiFe nanoparticles.

When using bifunctional core@shell catalysts, the stability of both the shell and core–shell interface is crucial for catalytic applications. In the present study, we elucidate the stability of a CuO/ZnO/Al2O3@ZSM-5 core@shell material, used for one-stage synthesis of dimethyl ether from synthesis gas. The catalyst stability was studied in a hierarchical manner by complementary environmental transmission electron microscopy (ETEM), scanning electron microscopy (SEM) andin situhard X-ray ptychography with a specially designedin situcell. Both reductive activation and reoxidation were applied. The core–shell interface was found to be stable during reducing and oxidizing treatment at 250°C as observed by ETEM andin situX-ray ptychography, although strong changes occurred in the core on a 10 nm scale due to the reduction of copper oxide to metallic copper particles. At 350°C,in situX-ray ptychography indicated the occurrence of structural changes also on theµm scale, i.e. the core material and parts of the shell undergo restructuring. Nevertheless, the crucial core–shell interface required for full bifunctionality appeared to remain stable. This study demonstrates the potential of these correlativein situmicroscopy techniques for hierarchically designed catalysts.

A novel nanoparticulate catalyst of copper (Cu) and ruthenium (Ru) was designed for low-temperature ammonia oxidation at near-stoichiometric mixtures using a bottom-up approach. A synergistic effect of the two metals was found. An optimum CuRu catalyst presents a reaction rate threefold higher than that for Ru and forty-fold higher than that for Cu. X-ray absorption spectroscopy suggests that in the most active catalyst Cu forms one or two monolayer thick patches on Ru and the catalysts are less active once 3D Cu islands form. The good performance of the tuned Cu/Ru catalyst is attributed to changes in the electronic structure, and thus the altered adsorption properties of the surface Cu sites.

In this work, we present a detailed study of the formation of supported intermetallic Ni–Ga catalysts for CO2 hydrogenation to methanol. The bimetallic phase is formed during a temperature-programmed reduction of the metal nitrates. By utilizing a combination of characterization techniques, in particular in situ and ex situ X-ray diffraction, in situ X-ray absorption spectroscopy, transmission electron microscopy combined with electron energy loss spectroscopy and X-ray fluorescence, we have studied the formation of intermetallic Ni–Ga catalysts of two compositions: NiGa and Ni5Ga3. These methods demonstrate that the catalysts with the desired intermetallic phase and composition are formed upon reduction in hydrogen and enable us to propose a mechanism of the Ni–Ga nanoparticles formation. By studying the effect of calcination prior to catalyst reduction, we show that the reactivity depends on particle size, which suggests that the reaction is structure sensitive.

Silica supported Cu–Ni (20 wt% Cu + Ni on silica, molar ratio of Cu/Ni = 2) alloys are prepared via impregnation, coprecipitation, and deposition–coprecipitation methods. The approach to co-precipitate the SiO2 from Na2SiO3 together with metal precursors is found to be an efficient way to prepare high surface area silica supported catalysts (BET surface area up to 322 m2 g−1, and metal area calculated from X-ray diffraction particle size up to 29 m2 g−1). The formation of bimetallic Cu–Ni alloy nanoparticles has been studied during reduction using in situ X-ray diffraction. Compared to impregnation, the coprecipitation and deposition–coprecipitation methods are more efficient for preparation of small and homogeneous Cu–Ni alloy nanoparticles. In order to examine the stability of Cu–Ni alloys in high pressure synthesis gas conversion, they have been tested for high pressure CO hydrogenation (50 bar CO and 50 bar H2). These alloy catalysts are highly selective (more than 99 mol%) and active for methanol synthesis; however, loss of Ni caused by nickel carbonyl formation is found to be a serious issue. The Ni carbonyl formation should be considered, if Ni-containing catalysts (even in alloyed form) are used under conditions with high partial pressure of CO.

Silica-supported, bimetallic Cu–Ni nanomaterials were prepared with different ratios of Cu to Ni by incipient wetness impregnation without a specific calcination step before reduction. Different in situ characterization techniques, in particular transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS), were applied to follow the reduction and alloying process of Cu–Ni nanoparticles on silica. In situ reduction of Cu–Ni samples with structural characterization by combined synchrotron XRD and XAS reveals a strong interaction between Cu and Ni species, which results in improved reducibility of the Ni species compared with monometallic Ni. At high Ni concentrations silica-supported Cu–Ni alloys form a homogeneous solid solution of Cu and Ni, whereas at lower Ni contents Cu and Ni are partly segregated and form metallic Cu and Cu–Ni alloy phases. Under the same reduction conditions, the particle sizes of reduced Cu–Ni alloys decrease with increasing Ni content. Estimates of the metal surface area from sulfur chemisorption and from the XRD particle size generally agree well on the trend across the composition range, but show some disparity in terms of the absolute magnitude of the metal area. This work provides practical synthesis guidelines towards preparation of Cu–Ni alloy nanomaterials with different Cu/Ni ratios, and insight into the application of different in situ techniques for characterization of the alloy formation.

Photocatalysts for solar fuel production are subject to intensive investigation as they constitute one viable route for solar energy harvesting. Cuprous oxide (Cu2O) is a working photocatalyst for hydrogen evolution but it photocorrodes upon light illumination in an aqueous environment. Environmental transmission electron microscopy (ETEM) makes it possible to obtain insight into the local structure, composition and reactivity of catalysts in their working environment, which is of fundamental interest for sustainable energy research and is essential for further material optimization. Herein, photoreduction of Cu2O is studied in situ using a dedicated TEM specimen holder for light illumination.

In situ reduction of nickel oxide (NiO) particles is performed under 1.3 mbar of hydrogen gas (H-2) in an environmental transmission electron microscope (ETEM). Images, diffraction patterns and electron energy-loss spectra (EELS) are acquired to monitor the structural and chemical evolution of the system during reduction, whilst increasing the temperature. Ni nucleation on NiO is either observed to be epitaxial or to involve the formation of randomly oriented grains. The growth of Ni crystallites and the movement of interfaces result in the formation of pores within the NiO grains to accommodate the volume shrinkage associated with the reduction. Densification is then observed when the sample is nearly fully reduced. The reaction kinetics is obtained using EELS by monitoring changes in the shapes of the Ni L-2,L-3 white lines. The activation energy for NiO reduction is calculated from the EELS data using both a physical model-fitting technique and a model-independent method. The results of the model-fitting procedure suggest that the reaction is described by Avrami models (whereby the growth and impingement of Ni domains control the reaction), in agreement with the ETEM observations.

We report the magnetic and transport properties of two promising half metallic/GaAs hybrid spintronic structures with respect to their structural features. The Co2 MnGa/GaAs(100) has shown a very low magnetic moment which is attributed to the columnar structure and the interface amorphous layer as from the HRTEM images. The out of plane hysteresis loops have shown a double switching which is related to the interface layer with different magnetic properties. In the Fe3O4/GaAs(100) system, the fast saturation of the magnetization indicates the low antiphase boundaries, which is supported by the HRTEM image. Furthermore, the moderate barrier height and the heavily damped processional response to the applied field pulses may be related to the interface structure.

Hybrid spintronic structures, integrating half-metallic magnetic oxides and Heusler alloys with their predicted high spin polarization, are important for the development of second-generation spintronics with high-efficient spin injection. We have synthesized epitaxial magnetic oxide Fe 3O 4 on GaAs(100) and the unit cell of the Fe3O4 was found to be rotated by 45deg to match the gallium arsenide GaAs. The films were found to have a bulk-like moment down to 3-4 nm and a low coercivity indicating a high-quality magnetic interface. The magnetization hysteresis loops of the ultrathin films are controlled by uniaxial magnetic anisotropy. The dynamic response of the sample shows a heavily damped precessional response to the applied field pulses. In the Heusler alloy system of Co2MnGa on GaAs, we found that the magnetic moment was reduced for thicknesses down to 10 nm, which may account for the lower than expected spin-injection efficiency from the spin-light-emitting diode structures. Using the element-specific technique of X-ray magnetic circular dichroism (XMCD), the reduced spin moments were found to originate from the Mn rather than the Co atoms, and the improvement of the interface is thus needed to increase the spin injection efficiency in this system. Further studies of the I-V characteristics of Fe3O4/GaAs(100) and Fe3O4/MgO/GaAs(100) show that the Fe3 O4 -based spintronic structures have a well-defined Schottky or tunneling barrier of moderate barrier height, which is encouraging for high-efficient spin injection.

A new closed cell is presented for in situ X-ray ptychography which allows studies under gas flow and at elevated temperature. In order to gain complementary information by transmission and scanning electron microscopy, the cell makes use of a Protochips E-chipTM which contains a small, thin electron transparent window and allows heating. Two gold-based systems, 50 nm gold particles and nanoporous gold as a relevant catalyst sample, were used for studying the feasibility of the cell. Measurements showing a resolution around 40 nm have been achieved under a flow of synthetic air and during heating up to temperatures of 933 K. An elevated temperature exhibited little influence on image quality and resolution. With this study, the potential of in situ hard X-ray ptychography for investigating annealing processes of real catalyst samples is demonstrated. Furthermore, the possibility to use the same sample holder for ex situ electron microscopy before and after the in situ study underlines the unique possibilities available with this combination of electron microscopy and X-ray microscopy on the same sample.

The catalytic activity and mobility of silver nanoparticles used as catalysts in temperature programmed oxidation of soot:silver (1:5 wt:wt) mixtures have been investigated by means of flow reactor experiments and in situ environmental transmission electron microscopy (ETEM). The carbon oxidation temperature was significantly lower compared to uncatalyzed soot oxidation with soot and silver loosely stirred together (loose contact) and lowered further with the two components crushed together (tight contact). The in situ TEM investigations revealed that the silver particles exhibited significant mobility during the soot oxidation, and this mobility, which increases the soot/catalyst contact, is expected to be an important factor for the lower oxidation temperature. In the intimate tight contact mixture the initial dispersion of the silver particles is greater,,and the onset of mobility occurs at a lower temperature which is consistent with the lower oxidation temperature of the tight contact mixture. (C) 2015 Elsevier B.V. All rights reserved.

A novel complementary approach of electron microscopy/environmental TEM and in situ hard X-ray ptychography was used to study the thermally induced coarsening of nanoporous gold under different atmospheres, pressures and after ceria deposition. The temperature applied during ptychographic imaging was determined by IR thermography. While using elevated temperatures (room temperature - 400 °C) and realistic gas atmospheres (1 bar) we achieved for the first time a spatial resolution of about 20 nm during hard X-ray ptychography. The annealing of pure and ceria stabilized nanoporous gold in different atmospheres revealed that the conditions have a tremendous influence on the coarsening. The porous structure of the samples was stable up to approximately 800 °C in vacuum, whereas pronounced changes and coarsening were observed already at approximately 300 °C in oxygen containing atmospheres. A layer of ceria on the nanoporous gold led to an improvement of the stability, but did not alleviate the influence of the gas atmosphere. Different behaviors were observed, such as coarsening and even material loss or migration. The results suggest that additional mechanisms beyond surface diffusion need to be considered and that microscopic studies aimed at more realistic conditions are important to understand the behavior of such materials and catalysts.

The effect of maghemization on the magnetic properties of magnetite (Fe3O4) grains in the pseudo-single-domain (PSD) size range is investigated as a function of annealing temperature. X-ray diffraction and transmission electron microscopy confirm the precursor grains as Fe3O4 ranging from 150 to 250 nm in diameter, whilst Mössbauer spectrometry suggests the grains are initially near-stoichiometric. The Fe3O4 grains are heated to increasing reaction temperatures of 120-220°C to investigate their oxidation to maghemite (γ-Fe2O3). High-angle annular dark field imaging and localized electron-energy loss spectroscopy reveal slightly oxidized Fe3O4 grains, heated to 140°C, exhibit higher oxygen content at the surface. Off-axis electron holography allows for construction of magnetic induction maps of individual Fe3O4 and γ-Fe2O3 grains, revealing their PSD (vortex) nature, which is supported by magnetic hysteresis measurements, including first-order reversal curve analysis. The coercivity of the grains is shown to increase with reaction temperature up to 180°C, but subsequently decreases after heating above 200°C; this magnetic behavior is attributed to the growth of a γ-Fe2O3 shell with magnetic properties distinct from the Fe3O4 core. It is suggested there is exchange coupling between these separate components that results in a vortex state with reduced vorticity. Once fully oxidized to γ-Fe2O3, the domain states revert back to vortices with slightly reduced coercivity. It is argued that due to a core/shell coupling mechanism during maghemization, the directional magnetic information will still be correct; however, the intensity information will not be retained. Key Points: Maghemization of Fe3O4 grains is confirmed through XRD, Mossbauer, and EELS Maghemization of Fe3O4 grains occurs through formation of a core-shell structure Magnetic behavior is considered due to core-shell exchange coupling

The magnetic properties of the ferrite Mn0.25Zn0.75Fe2O4 have been studied by Mossbauer spectroscopy and magnetisation measurements. Mossbauer spectra, obtained at low temperatures and large applied magnetic fields, showed that almost all Fe3+ ions are in octahedral (B) sites and only about 2% of the Fe3+ ions are in tetrahedral (A) sites. At 5 K about 16% of the B-site Fe3+ ions have spins parallel to the A-site magnetisation, but when the temperature is raised to about 40 K, these spins are reversed. Some other B-site Fe3+ ions show a large spin canting at 5 K and these ions are significantly affected by transverse relaxation at relatively low temperatures. A third group of B-site ions has negligible canting at low temperatures and these ions are only slightly affected by relaxation below 60 K. At low temperatures the material can be described as a cluster spin glass. Above 60 K part of the sample breaks up into superparamagnetic clusters whereas other parts remain ferrimagnetic.

Specimen transfer under controlled environment conditions, such as temperature, pressure, and gas composition, is necessary to conduct successive complementary in situ characterization of materials sensitive to ambient conditions. The in situ transfer concept is introduced by linking an environmental transmission electron microscope to an in situ X-ray diffractometer through a dedicated transmission electron microscope specimen transfer holder, capable of sealing the specimen in a gaseous environment at elevated temperatures. Two catalyst material systems have been investigated; Cu/ZnO/Al2O3 catalyst for methanol synthesis and a Co/Al2O3 catalyst for Fischer–Tropsch synthesis. Both systems are sensitive to ambient atmosphere as they will oxidize after relatively short air exposure. The Cu/ZnO/Al2O3 catalyst, was reduced in the in situ X-ray diffractometer set-up, and subsequently, successfully transferred in a reactive environment to the environmental transmission electron microscope where further analysis on the local scale were conducted. The Co/Al2O3 catalyst was reduced in the environmental microscope and successfully kept reduced outside the microscope in a reactive environment. The in situ transfer holder facilitates complimentary in situ experiments of the same specimen without changing the specimen state during transfer.

The long term stability and resistance toward carbon deposition, sulfur, chlorine, and potassium of Ni/ZrO2 as a catalyst for the hydrodeoxygenation (HDO) of guaiacol in 1-octanol (as a model compound system for bio-oil) has been investigated at 250 degrees C and 100 bar in a trickle bed reactor setup. Without impurities in the feed good stability of the Ni/ZrO2 catalyst could be achieved over more than 100 h of operation, particularly for a sample prepared with small Ni particles, which minimized carbon deposition. Exposing the catalyst to 0.05 wt% sulfur in the feed resulted in rapid deactivation with complete loss of activity due to the formation of nickel sulfide. Exposing Ni/ZrO2 to chlorine-containing compounds (at a concentration of 0.05 wt% Cl) on-stream led to a steady decrease in activity over 40 h of exposure. Removal of the chlorine species from the feed led to the regaining of activity. Analysis of the spent catalyst revealed that the adsorption of chlorine on the catalyst was completely reversible, but chlorine had caused sintering of nickel particles. In two experiments, potassium, as either KCl or KNO3, was impregnated on the catalyst prior to testing. In both cases deactivation was persistent over more than 20 h of testing and severely decreased the deoxygenation activity while the hydrogenation of guaiacol was unaffected. Overall, sulfur was found to be the worst poison, followed by potassium and then chlorine. Thus, removal/limitation of these species from bio-oil is a requirement before long term operation can be achieved with this catalyst.

Metallic alloy nanoparticles (NPs) are synthesized in situ in an environmental transmission electron microscope. Atomic level characterization of the formed alloy NPs is carried out at synthesis conditions by use of high-resolution transmission electron microscopy, electron diffraction and electron energy-loss spectroscopy.

Hydrodeoxygenation (HDO) is proposed as an efficient way to remove oxygen in bio-oil, improving its quality as a more sustainable alternative to conventional fuels in terms of CO2 neutrality and relative short production cycle [1].Ni and Ni-MoS2 nanoparticles supported on ZrO2 show potential as high-pressure (100 bar) catalysts for purification of bio-oil by HDO. However, the catalysts deactivate in presence of sulfur, chlorine and potassium species, which are all naturally occurring in real bio-oil.The deactivation mechanisms of the Ni/ZrO2 have been investigated through scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Catalytic testing has been performed using guaiacol in 1-octanol acting as a model compound for bio-oil.Addition of sulphur (0.3 vol% octanethiol) in the feed resulted in permanent deactivation of the catalyst by formation of a catalytically inactive Ni-S phase, as suggested by the very similar spatial distribution of nickel and sulphur signals in STEM-EDX elemental maps (Figure 1) and confirmed by XRD and X-ray absorption spectroscopy (XAS) techniques.Deactivation by chlorine (0.3 vol% chlorooctane) co-feeding was found to be reversible, as the catalyst could regain close to its initial deoxygenation activity upon restoration of a clean feed. SEM-EDX investigations excluded the presence of chlorine species; however, XRD analysis revealed sintering of nickel nanoparticles (Figure 2).Impregnating KCl and KNO3 on two different batches of catalysts decreased permanently their deoxygenation activity, suggesting the adsorption of potassium at low coordinated nickel sites [2]. The high mobility of potassium under the electron beam [3] prevented the spatial distribution study of this element through STEM-EDX. Moreover, nickel sintering was observed in the KCl poisoned sample and was ascribed once again to the formation of mobile Ni-Cl species upon reaction of HCl with surface oxides [4].Furthermore, environmental transmission electron microscopy (ETEM) has been used in order to investigate the oxidation of Ni-MoS2/ZrO2 catalyst active phase as a function of different HDO reaction conditions and using methanol as a model molecule for bio-oil.

We have grown 4 nm thin films of 57 Fe on InAs(100) and InP(100) surfaces by use of MBE and studied the samples by 57 Fe conversion electron Mossbauer spectroscopy. In the case of InAs, the Mossbauer spectrum showed a sextet due to α-Fe and a further magnetically split component with slightly smaller hyperfine field, which is attributed to interface components. This result indicates that there is a relatively sharp interface between Fe and InAs. On the contrary, the spectrum of the InP sample showed a sextet with very broad lines and a smaller average hyperfine field. This suggests a strong chemical reaction between iron and the substrate, which results in the formation of a poorly crystalline phase.

Nickel oxide reduction and subsequent Ni behaviour under H2 is of practical importance in the field of solid oxide fuel cell (SOFC) technology, as it determines the structure of the electronic conductor on the anode side during operation [1]. Despite extensive coverage in the literature [2], several questions remain, notably regarding the NiO reduction kinetics and its structural evolution.Here, we perform in situ reduction of an industrial NiO powder from JT Baker™ under 1.3 mbar of H2 (2 mlN/min) in a differentially pumped FEI Titan environmental transmission electron microscope (ETEM) [3]. Images, diffraction patterns and electron energy-loss spectra are acquired during different temperature ramps (300 to 600°C) in order to monitor the structural and chemical evolution of the system. Similar experiments are performed in a PANalytical X'Pert PRO X-ray diffractometer equipped with an Anton Paar furnace and a mass spectrometer to complement and extrapolate the ETEM data to higher pressures and gas flows. Diffraction peak intensities, crystallite sizes (obtained using the Scherrer formula) and H2/H2O mass spectrometer signals are monitored.The recorded images and diffraction patterns show that the nucleation of Ni on NiO takes place at temperatures below 400°C and is either epitaxial with a small angle misfit in thin specimen areas (Fig. 1) or randomly oriented in thicker regions. Reduction proceeds through the growth of Ni domains and the movement of interfaces, the latter inducing particle shrinkage and pore creation within larger particles. Densification is observed when the temperature approaches 600°C: the porosity that was created at lower temperatures disappears. This reorganization of Ni is detrimental to the connectivity of the Ni catalyst and to the reduction-reoxidation stability of the SOFC [4].Reaction kinetics are measured in the ETEM by electron energy-loss spectroscopy using two different techniques based on changes of the Ni L2,3 white lines upon reduction (either taking the ratio of the Ni L3 and L2 integrated intensities or using multiple linear least squares fitting of NiO and Ni experimental reference spectra [5,6]). Reduction starts earlier but at a higher temperature when the heating rate is increased (380°C at 2°C/min compared to 420°C at 7°C/min). The initiation of the reduction depends on the number of oxygen surface vacancies, which in turn depends on the temperature and time [7]. Reduction proceeds quickly until the remaining NiO fraction reaches a level of about 30% (Fig. 2). The reaction then slows down and full reduction is only achieved at temperatures above 600°C (confirmed using diffraction). This decrease in reaction rate appears to be caused by physical factors, as NiO reduction is known to be autocatalytic [2]. As only a few micrograms of reducible material are dispersed on the TEM grid and considering the volume of the reaction chamber in the ETEM (~800 cm3), a shortage of reactive gas is unlikely even in 2 mbar of H2. It is probable that the presence and stagnation of H2O vapour created upon reduction blocks H2 access to the reactive sites, decreasing the reaction rate at a high conversion fraction. The gas flow is low and may not evacuate the product gas efficiently around the Ni(O) particles. Complementary XRD experiments point towards the same conclusion and underline the impact of the pressure and gas flow on the kinetics.It is possible to determine an approximate activation energy for NiO reduction inside the ETEM using the Kissinger method [8], which is based on measurements of the shift in the temperature at which the reaction rate is maximum for different heating rates. With EELS experiments performed at 2, 4 and 7 °C/min, an activation energy of ~70 ± 20 kJ/mol is obtained, which is consistent with values found in the literature [2].

In situ reduction of an industrial NiO powder is performed under 1.3 mbar of H2 (2 mlN/min) in a differentially pumped FEI Titan 80-300 environmental transmission electron microscope (ETEM). Images, diffraction patterns and electron energy loss spectra (EELS) are acquired to monitor the structural and chemical evolution of the system during different temperature ramps (at 2, 4 and 7°C/min). High-resolution ETEM is also performed during similar experiments.Ni nucleation on NiO is observed to be either epitaxial in thin areas or randomly oriented on thicker regions and when nucleation is more advanced. The growth of Ni crystallites and the movement of interfaces create pores within the NiO grains to accommodate the volume shrinkage associated with the reduction. EELS analysis illustrates that reduction proceeds quickly at temperatures below 400°C up to a reduced fraction of about 0.6, until the reaction is slowed down by water created upon reduction. Using the data obtained at different heating rates and the Kissinger method, an activation energy for the NiO reduction of 70 ± 20 kJ/mol could be obtained. Densification is then observed at temperatures higher than 550°C: pores created at lower temperatures disappear and Ni grains coarsen. This reorganization of Ni is detrimental to both the connectivity of the Ni catalyst and to the redox stability of the SOFC. A model for the structural evolution of NiO under H2 is proposed.

This paper presents a simple procedure for simultaneous cutting and forming of thin Al foils for use in MEMS components. The procedure makes use of scaled down macroscopic sheet forming and cutting techniques by using a hydraulic press, a soft counterpart, and a microfabricated stamp tool. The relation between applied pressure and forming and cutting features has been characterized for a specific set of stamp geometries and boundary conditions. The results show that 10 μm forming features can be transferred to 4 μm thick Al foils, which simultaneously can be cut into products by 25 μm wide cut lines. Using the procedure presented in this paper scaled to full 4–8 in. silicon wafer stamp tools, a fast and adequate method for high volume production of MEMS components is obtained.

A sample processing device is disclosed, which sample processing device comprises a first substrate and a second substrate, where the first substrate has a first surface comprising two area types, a first area type with a first contact angle with water and a second area type with a second contact angle with water, the first contact angle being smaller than the second contact angle. The first substrate defines an inlet system and a preparation system in areas of the first type which two areas are separated by a barrier system in an area of the second type. The inlet system is adapted to receive a sample liquid comprising the sample and the first preparation system is adapted to receive a receiving liquid. In a particular embodiment, a magnetic sample transport component, such as a permanent magnet or an electromagnet, is arranged to move magnetic beads in between the first and second substrates.

Magnetorelaxometry measurements on suspensions of magnetic beads are demonstrated using a planar Hall effect sensor chip embedded in a microfluidic system. The alternating magnetic field used for magnetizing the beads is provided by the sensor bias current and the complex magnetic susceptibility spectra are recorded as the 2nd harmonic of the sensor response. The complex magnetic susceptibility signal appears when a magnetic bead suspension is injected, it scales with the bead concentration, and it follows the Cole-Cole expression for Brownian relaxation. The complex magnetic susceptibility signal resembles that from conventional magnetorelaxometry done on the same samples apart from an offset in Brownian relaxation frequency. The time dependence of the signal can be rationalized as originating from sedimented beads.