A new high temperature, high heating rate, low axial gradient capillary heater.

A new heater design, capable of fast heating and cooling to and from >1000°C, has been developed at the Swiss-Norwegian Beamlines, European Synchrotron Radiation Facility, France. The design uses a SiC head to distribute heat, and resistive Si3N4 heat cartridges to provide heat.

Understanding the Hydrothermal Formation of NaNbO3: Its Full Reaction Scheme and Kinetics.

Sodium niobate (NaNbO3) attracts attention for its great potential in a variety of applications, for instance, due to its unique optical properties. Still, optimization of its synthetic procedures is hard due to the lack of understanding of the formation mechanism under hydrothermal conditions. Through in situ X-ray diffraction, hydrothermal synthesis of NaNbO3 was observed in real time, enabling the investigation of the reaction kinetics and mechanisms with respect to temperature and NaOH concentration and the resulting effect on the product crystallite size and structure. Several intermediate phases were observed, and the relationship between them, depending on temperature, time, and NaOH concentration, was established. The reaction mechanism involved a gradual change of the local structure of the solid Nb2O5 precursor upon suspending it in NaOH solutions. Heating gave a full transformation of the precursor to HNa7Nb6O19·15H2O, which destabilized before new polyoxoniobates appeared, whose structure depended on the NaOH concentration. Following these polyoxoniobates, Na2Nb2O6·H2O formed, which dehydrated at temperatures ≥285 °C, before converting to the final phase, NaNbO3. The total reaction rate increased with decreasing NaOH concentration and increasing temperature. Two distinctly different growth regimes for NaNbO3 were observed, depending on the observed phase evolution, for temperatures below and above ≈285 °C. Below this temperature, the growth of NaNbO3 was independent of the reaction temperature and the NaOH concentration, while for temperatures ≥285 °C, the temperature-dependent crystallite size showed the characteristics of a typical dissolution-precipitation mechanism.

A Fast, Low-Temperature Synthesis Method for Hexagonal YMnO3 : Kinetics, Purity, Size and Shape as Studied by In Situ X-ray Diffraction.

The reaction mechanisms, phase development and kinetics of the hydrothermal synthesis of hexagonal-YMnO3 from Y2 O3 and Mn2 O3 using in situ X-ray diffraction are reported under different reaction conditions with temperatures ranging from 300 to 350 °C, and using 1, 5 and 10 m KOH, and 5 m NaOH mineraliser. Reactions initiated with Y2 O3 hydrating to Y(OH)3 , which then dehydrated to YO(OH). Higher temperatures and KOH concentrations led to faster, more complete dehydrations. However, 1 m KOH led to YO(OH) forming concurrently with Y(OH)3 before Y(OH)3 fully dehydrated but yielded a very low phase purity of hexagonal-YMnO3 . Using NaOH mineraliser, no YO(OH) was observed. Dehydration also initiated at a higher temperature in the absence of Mn2 O3 . The evolution of Rietveld refined scale factors was used to determine kinetic information and approximate activation energies for the reaction. The described hydrothermal synthesis offers a fast, low-temperature method for producing anisometric h-YMnO3 particles.

Unwanted effects of X-rays in surface grafted copper(ii) organometallics and copper exchanged zeolites, how they manifest, and what can be done about them.

Copper(ii) containing materials are widely studied for a very diverse array of applications from biology, through catalysis, to many other materials chemistry based applications. We show that, for grafted copper compounds at the surface of silica, and for the study of the selective conversion of methane to methanol using copper ion-exchanged zeolites, the application of focused X-ray beams for spectroscopic investigations is subject to significant challenges. We demonstrate how unwanted effects due to the X-rays manifest, which can prevent the study of certain types of reactive systems, and/or lead to the derivation of results that are not at all representative of the behavior of the materials in question. With reference to identical studies conducted at a beamline that does not focus its X-rays, we then delineate how the total photon throughput and the brilliance of the applied X-rays affect the apparent behavior of copper in zeolites during the stepwise, high temperature and aerobic activation approach to the selective conversion of methane to methanol. We show that the use of increasingly brilliant X-ray sources for X-ray spectroscopy can bring with it significant caveats to obtaining valid and quantitative structure-reactivity relationships (QSARS) and kinetics for this class of material. Lastly, through a systematic study of these effects, we suggest ways to ensure that valuable allocations of X-ray beam time result in measurements that reflect the real nature of the chemistry under study and not that due to other, extraneous, factors.

Insights into Reaction Intermediates to Predict Synthetic Pathways for Shape-Controlled Metal Nanocrystals.

Understanding nucleation phenomena is crucial across all branches of physical and natural sciences. Colloidal nanocrystals are among the most versatile and tunable synthetic nanomaterials. While huge steps have been made in their synthetic development, synthesis by design is still impeded by the lack of knowledge of reaction mechanisms. Here, we report on the investigation of the reaction intermediates in high temperature syntheses of copper nanocrystals by a variety of techniques, including X-ray absorption at a synchrotron source using a customized in situ cell. We reveal unique insights into the chemical nature of the reaction intermediates and into their role in determining the final shape of the metal nanocrystals. Overall, this study highlights the importance of understanding the chemistry behind nucleation as a key parameter to predict synthetic pathways for shape-controlled nanocrystals.

The effect of copper on the redox behaviour of iron oxide for chemical-looping hydrogen production probed by in situ X-ray absorption spectroscopy.

The production of high purity hydrogen with the simultaneous capture of CO2, can be achieved through a chemical looping (CL) cycle relying on an iron oxide-based oxygen carrier. Indeed, the availability of active and cyclically stable oxygen carriers is a key criterion for the practical implementation of this technology. In this regard, improving our understanding of the reduction pathway(s) of iron-based oxygen carriers and the development of concepts to increase the reduction kinetics are important aspects. The aim of this work is to evaluate the effect of the addition of copper on the redox behaviour of iron oxide based oxygen carriers stabilized on ZrO2. In situ pulsed-H2 XANES (Fe K-edge) experiments allowed for the determination of the reduction pathways in these materials, viz. the reduction of both Fe2O3 and CuFe2O4 proceeded via a Fe2+ intermediate: Fe2O3 (CuFe2O4) → Fe3O4 (Cu0) → FeO (Cu0) → Fe0 (Cu0). In the first step CuFe2O4 is reduced to Cu0 and Fe3O4, whereby Cu0 promotes the further reduction of iron oxide, increasing their rate of formation. In particular, the rate of reduction of FeO → Fe0 is accelerated most dramatically by Cu0. This is an encouraging result as the FeO → Fe0 transition is the slowest reduction reaction.

Evaluation of Reoxidation Thresholds for γ-Al2O3-Supported Cobalt Catalysts under Fischer-Tropsch Synthesis Conditions.

Size-dependent phenomena at the nanoscale influence many applications, notably in the science of heterogeneous catalysis. In cobalt-based Fischer-Tropsch synthesis (FTS), the size of Co nanoparticles (NPs) dictates to a high degree catalyst's performance in terms of activity, selectivity, and stability. Here, a highly dispersed Re/Co/γ-Al2O3 catalyst with high Co surface area per gram of catalyst was exposed to industrially relevant FTS conditions and monitored in situ by synchrotron X-ray radiation. X-ray absorption near-edge structure spectra were obtained on the cobalt K edge and Re L3 edge of the working catalyst. The experimental results demonstrate development of tetrahedrally coordinated Co2+ forming at the expense of metallic Co(0). The structure of the oxide resembles CoAl2O4 and appears at the onset (first 5-10 h) of the reaction. Reoxidation of Co(0) is more pronounced close to the outlet of the reactor, where higher pH2O is anticipated. The state of the Re promoter does not change during the FT process. We propose that reoxidation of small Co NPs is followed by spreading of Co oxide that leads to the formation of CoxAlyOz phases. Hence, in order to avoid an irreversible loss of the active phase during process start-up, catalyst design should be restricted to Co NPs larger than 5.3 nm.

Cooperativity and Dynamics Increase the Performance of NiFe Dry Reforming Catalysts.

The dry reforming of methane (DRM), i.e., the reaction of methane and CO2 to form a synthesis gas, converts two major greenhouse gases into a useful chemical feedstock. In this work, we probe the effect and role of Fe in bimetallic NiFe dry reforming catalysts. To this end, monometallic Ni, Fe, and bimetallic Ni-Fe catalysts supported on a MgxAlyOz matrix derived via a hydrotalcite-like precursor were synthesized. Importantly, the textural features of the catalysts, i.e., the specific surface area (172-178 m2/gcat), pore volume (0.51-0.66 cm3/gcat), and particle size (5.4-5.8 nm) were kept constant. Bimetallic, Ni4Fe1 with Ni/(Ni + Fe) = 0.8, showed the highest activity and stability, whereas rapid deactivation and a low catalytic activity were observed for monometallic Ni and Fe catalysts, respectively. XRD, Raman, TPO, and TEM analysis confirmed that the deactivation of monometallic Ni catalysts was in large due to the formation of graphitic carbon. The promoting effect of Fe in bimetallic Ni-Fe was elucidated by combining operando XRD and XAS analyses and energy-dispersive X-ray spectroscopy complemented with density functional theory calculations. Under dry reforming conditions, Fe is oxidized partially to FeO leading to a partial dealloying and formation of a Ni-richer NiFe alloy. Fe migrates leading to the formation of FeO preferentially at the surface. Experiments in an inert helium atmosphere confirm that FeO reacts via a redox mechanism with carbon deposits forming CO, whereby the reduced Fe restores the original Ni-Fe alloy. Owing to the high activity of the material and the absence of any XRD signature of FeO, it is very likely that FeO is formed as small domains of a few atom layer thickness covering a fraction of the surface of the Ni-rich particles, ensuring a close proximity of the carbon removal (FeO) and methane activation (Ni) sites.

A Binuclear Zinc Interaction Fold Discovered in the Homodimer of Alzheimer's Amyloid-ß Fragment with Taiwanese Mutation D7H.

Zinc-induced oligomerization of amyloid-ß peptide (Aß) produces potentially pathogenic agents of Alzheimer's disease. Mutations and modifications in the metal binding domain 1-16 of Aß peptide crucially affect its zinc-induced oligomerization by changing intermolecular zinc mediated interface. The 3D structure of this interface appearing in a range of Aß species is a prospective drug target for disease modifying therapy. Using NMR spectroscopy, EXAFS spectroscopy, mass spectrometry, and isothermal titration calorimetry the interaction of zinc ions with Aß fragments 1-7 and 1-10 carrying familial Taiwanese mutation D7H was studied. Zinc ions induce formation of a stable homodimer formed by the two peptide chains fastened by two zinc ions and stacking interactions of imidazole rings. A binuclear zinc interaction fold in the dimer structure was discovered. It can be used for designing zinc-regulated proteins and zinc-mediated self-assembling peptides.

Elucidating the Impact of Li3InCl6-Coated LiNi0.8Co0.15Al0.05O2 on the Electro-Chemo-Mechanics of Li6PS5Cl-Based Solid-State Batteries.

Li6PS5Cl has attracted significant attention due to its high Li-ion conductivity and processability, facilitating large-scale solid-state battery applications. However, when paired with high-voltage cathodes, it experiences adverse side reactions. Li3InCl6 (LIC), known for its higher stability at high voltages and moderate Li-ion conductivity, is considered a catholyte to address the limitations of Li6PS5Cl. To extend the stability of Li6PS5Cl toward LiNi0.8Co0.15Al0.05O2 (NCA), we applied nanocrystalline LIC as a 180 nm-thick protective coating in a core-shell-like fashion (LIC@NCA) via mechanofusion. Solid-state batteries with LIC@NCA allow an initial discharge specific capacity of 148 mA h/g at 0.1C and 80% capacity retention for 200 cycles at 0.2C with a cutoff voltage of 4.2 V (vs Li/Li+), while cells without LIC coating suffers from low initial discharge capacity and poor retention. Using a wide spectrum of advanced characterization techniques, such as operando XRD, XPS, FIB-SEM, and TOF-SIMS, we reveal that the superior performance of solid-state batteries employing LIC@NCA is related to the suppression of detrimental interfacial reactions of NCA with Li6PS5Cl, delamination, and particle cracking compared to uncoated NCA.

Dimethyl carbonate synthesis from CO2 and methanol over CeO2: elucidating the surface intermediates and oxygen vacancy-assisted reaction mechanism.

Surface intermediate species and oxygen vacancy-assisted mechanism over CeO2 catalyst in the direct dimethyl carbonate (DMC) synthesis from carbon dioxide and methanol are suggested by means of transient spectroscopic methodologies in conjunction with multivariate spectral analysis. How the two reactants, i.e. CO2 and methanol, interact with the CeO2 surface and how they form decisive surface intermediates leading to DMC are unraveled by DFT-based molecular dynamics simulation by precise statistical sampling of various configurations of surface states and intermediates. The atomistic simulations and uncovered stability of different intermediate states perfectly explain the unique DMC formation profile experimentally observed upon transient operations, strongly supporting the proposed oxygen vacancy-assisted reaction mechanism.

Pyrochlore-Type Iron Hydroxy Fluorides as Low-Cost Lithium-Ion Cathode Materials for Stationary Energy Storage.

Pyrochlore-type iron (III) hydroxy fluorides (Pyr-IHF) are appealing low-cost stationary energy storage materials due to the virtually unlimited supply of their constituent elements, their high energy densities, and fast Li-ion diffusion. However, the prohibitively high costs of synthesis and cathode architecture currently prevent their commercial use in low-cost Li-ion batteries. Herein, a facile and cost-effective dissolution-precipitation synthesis of Pyr-IHF from soluble iron (III) fluoride precursors is presented. High capacity retention by synthesized Pyr-IHF of >80% after 600 cycles at a high current density of 1 A g-1 is obtained, without elaborate electrode engineering. Operando synchrotron X-ray diffraction guides the selective synthesis of Pyr-IHF such that different water contents can be tested for their effect on the rate capability. Li-ion diffusion is found to occur in the 3D hexagonal channels of Pyr-IHF, formed by corner-sharing FeF6-x (OH)x octahedra.

The more the better: on the formation of single-phase high entropy alloy nanoparticles as catalysts for the oxygen reduction reaction.

High entropy alloys (HEAs) are an important new material class with significant application potential in catalysis and electrocatalysis. The entropy-driven formation of HEA materials requires high temperatures and controlled cooling rates. However, catalysts in general also require highly dispersed materials, i.e., nanoparticles. Only then a favorable utilization of the expensive raw materials can be achieved. Several recently reported HEA nanoparticle synthesis strategies, therefore, avoid the high-temperature regime to prevent particle growth. In our work, we investigate a system of five noble metal single-source precursors with superior catalytic activity for the oxygen reduction reaction. Combining in situ X-ray powder diffraction with multi-edge X-ray absorption spectroscopy, we address the fundamental question of how single-phase HEA nanoparticles can form at low temperatures. It is demonstrated that the formation of HEA nanoparticles is governed by stochastic principles and the inhibition of precursor mobility during the formation process favors the formation of a single phase. The proposed formation principle is supported by simulations of the nanoparticle formation in a randomized process, rationalizing the experimentally found differences between two-element and multi-element metal precursor mixtures.

Scientific opportunities for heterogeneous catalysis research at the SuperXAS and SNBL beam lines.

In this short review, we describe the complementary experimental capabilities for catalysis research at two beam lines available to the Swiss community, SuperXAS at SLS (Swiss Light Source, Villigen) and SNBL (Swiss Norwegian Beam lines) at ESRF (European Synchrotron Radiation Facility, Grenoble). Over the years, these two facilities have been developed to provide powerful techniques for structural studies under in situ and operando conditions. These techniques, X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and X-ray emission spectroscopy (XES) in combination with Raman or infrared spectroscopy provide new avenues for structure-performance studies of catalysts. Several exemplary studies are used to demonstrate the capability of these facilities.

Coupled commensurate cation and charge modulation in the tunneled structure, Na(0.40(2))MnO(2).

Na(0.40(2))MnO(2) belongs to a family of mixed Mn(3+) and Mn(4+) porous oxides that contains both octahedral and square pyramidal Mn-O units. Neutron and synchrotron radiation studies identify the presence of both sodium ordering (T(Na) ≈ 310 K) and Mn charge and orbital ordering. Below T(Na), the centrosymmetric Pbam structure adopts an (ab 4c) supercell of Pnnm symmetry that accommodates a coupled commensurate modulation down the c-axis channels of both Na position and occupancy with Mn valence.

Combining synchrotron-based X-ray techniques with vibrational spectroscopies for the in situ study of heterogeneous catalysts: a view from a bridge.

The advantages, challenges, and future possibilities for combining synchrotron-based X-ray techniques with vibrational spectroscopies are considered in this critical review. Particular emphasis is given to (1) quantifying structure and structural change--on a wide range of length scales--in working heterogeneous catalytic systems; (2) relating that change to chemical speciation occurring at the surface of the catalyst; and (3) determining how such change relates to the overall function of the catalyst material. We will consider those resources that exist today and suggest some possible future directions yet to be ventured into or demonstrated. Lastly, we will consider how the catalysis community interacts with, and uses the resources offered by, modern synchrotron radiation facilities and whether this current relationship provides the best and most inclusive means for the exploitation of these resources in this field of research (83 references).

On the resolution function for powder diffraction with area detectors.

In a powder diffraction experiment the resolution function defines the instrumental contribution to the peak widths as a function of the Bragg angle. The Caglioti formula is frequently applied to model the instrumental broadening and used in structural refinement. The parameters in the Caglioti formula are linked to physically meaningful parameters for most diffraction geometries. However, this link is lost for the now very popular powder diffraction geometry using large 2D area detectors. Here we suggest a new physical model for the instrumental broadening specifically developed for powder diffraction data measured with large 2D area detectors. The model is verified using data from two synchrotron diffraction beamlines with the Pilatus2M and MAR345 detectors. Finally, a functional form is proposed to replace the Caglioti formula for this geometry in the Rietveld method and profile refinements.

Stability and reactivity of ϵ-χ-θ iron carbide catalyst phases in Fischer-Tropsch synthesis: controlling µ(C).

The stability and reactivity of ϵ, χ, and θ iron carbide phases in Fischer-Tropsch synthesis (FTS) catalysts as a function of relevant reaction conditions was investigated by a synergistic combination of experimental and theoretical methods. Combined in situ X-ray Absorption Fine Structure Spectroscopy/X-ray Diffraction/Raman Spectroscopy was applied to study Fe-based catalysts during pretreatment and, for the first time, at relevant high pressure Fischer-Tropsch synthesis conditions, while Density Functional Theory calculations formed a fundamental basis for understanding the influence of pretreatment and FTS conditions on the formation of bulk iron carbide phases. By combining theory and experiment, it was found that the formation of θ-Fe(3)C, χ-Fe(5)C(2), and ϵ-carbides can be explained by their relative thermodynamic stability as imposed by gas phase composition and temperature. Furthermore, it was shown that a significant part of the Fe phases was present as amorphous carbide phases during high pressure FTS, sometimes in an equivalent amount to the crystalline iron carbide fraction. A catalyst containing mainly crystalline χ-Fe(5)C(2) was highly susceptible to oxidation during FTS conditions, while a catalyst containing θ-Fe(3)C and amorphous carbide phases showed a lower activity and selectivity, mainly due to the buildup of carbonaceous deposits on the catalyst surface, suggesting that amorphous phases and the resulting textural properties play an important role in determining final catalyst performance. The findings further uncovered the thermodynamic and kinetic factors inducing the ϵ-χ-θ carbide transformation as a function of the carbon chemical potential µ(C).

Tracking the formation of cobalt substituted ALPO-5 using simultaneous in situ X-ray diffraction and X-ray absorption spectroscopy techniques.

We followed the formation of metal ion substituted aluminophosphate, a redox molecular sieve, using a newly developed in situ simultaneous X-ray diffraction and X-ray absorption spectroscopic technique. The study showed that a cobalt-phosphorous network forms prior to the crystallisation.

Co-adsorption and separation of CO2-CH4 mixtures in the highly flexible MIL-53(Cr) MOF.

The present study attempts to understand the use of the flexible porous chromium terephthalate Cr(OH)(O(2)C-C(6)H(4)-CO(2)) denoted MIL-53(Cr) (MIL = Material from Institut Lavoisier) for the separation of mixtures of CO(2) and CH(4) at ambient temperature. The coadsorption of CO(2) and CH(4) was studied by a variety of different techniques. In situ synchrotron X-ray Powder Diffraction allowed study of the breathing of the solid upon adsorption of the gas mixtures and simultaneously measured Raman spectra yielded an estimation of the adsorbed quantities of CO(2) and CH(4), as well as a quantification of the fraction of the narrow pore (NP) and the large pore (LP) form of MIL-53. Quantitative coadsorption data were then measured by gravimetry and by breakthrough curves. In addition, computer simulation was performed to calculate the composition of the adsorbed phase in comparison with experimental equilibrium isotherms and breakthrough results. The body of results shows that the coadsorption of CO(2) and CH(4) leads to a similar breathing of MIL-53(Cr) as with pure CO(2). The breathing is mainly controlled by the partial pressure of CO(2), but increasing the CH(4) content progressively decreases the transformation of LP to NP. CH(4) seems to be excluded from the NP form, which is filled exclusively by CO(2) molecules. The consequences in terms of CO(2)/CH(4) selectivity and the possible use of MIL-53(Cr) in a PSA process are discussed.