[This corrects the article DOI: 10.1371/journal.pone.0323678.].

A plug-flow fixed-bed cell for operando laboratory X-ray absorption spectroscopy (XAS) using a von H & aacute;mos spectrometer is presented for heterogeneous catalysis studies. The cell operates up to 1000 degrees C and 10 bar with controlled gas atmospheres provided by three mass flow controllers and rapid infrared heating. The performance of the setup is demonstrated across a broad usable energy range of the spectrometer, and as a proof of principle, operando Ni K-edge XAS was used to monitor the activation of a 20 wt% NiO/COK-12 catalyst under CO2 methanation conditions (CO2 : H2 = 1 : 4, 350 degrees C). Time-resolved spectra acquired on a 5 min timescale reveal the reduction of NiO nanoparticles to metallic Ni during activation, directly correlating with increasing catalytic activity quantified by online gas chromatography. This setup enables minute-scale, time-resolved structural analysis of working catalysts under industrially relevant conditions, providing a practical laboratory-based alternative complementary to synchrotron studies.

The capabilities of a plug-flow fixed-bed cell for operando studies of heterogeneous catalysts are demonstrated using laboratory-based X-ray absorption spectroscopy (XAS) with a von Hamos spectrometer. The cell operates at temperatures up to 1000 deg C and pressures up to 10 bar, equipped with three mass flow controllers and two infrared lamps for rapid heating under inert/reactive gas atmospheres. Proof-of-principle studies include in situ MnO oxidation in 5

Controlling the particle size and stability under reaction conditions is crucial for increasing catalyst lifetime and producing more sustainable chemical processes. In this work, Cu oxide nanoparticles were confined in three distinct supports: MCF (mesocellular foam) silica, layers of carbon nitride on the surface of mesoporous silica (MCF-CN), or layers of P-doped carbon nitride (MCF-CN-P). The carbon nitride coating was produced using cyanamide, and P-doped carbon nitride was created from a mixture of cyanamide and sodium hypophosphite. The different supports were used to investigate their effects on the distribution, size, and stability of Cu-based particles in the selective oxidation of alcohols, employing peroxymonosulfate (PMS) as the oxidizing agent. Primary and secondary alcohols such as cyclohexanol, benzyl alcohol, and 4-hydroxy-3,5-dimethoxybenzyl alcohol were used as substrates. The synthesized layers of P-doped carbon nitride enhance the conversion of alcohols to their respective ketones or aldehydes, achieving conversions above 80% and selectivity above 90%. Moreover, the stability of copper oxide increases compared with particles deposited on pristine silica.

Alkaline zinc-air batteries (ZABs) have attracted interest in recent years for their high theoretical energy density and use of low-cost, abundant zinc metal as the anode. In order to overcome the activation energy barrier of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), noble metals are commonly used. Within this work, transition metal-functionalized Poly(heptazine imide)s (PHIs) are studied as an alternative and more abundant electrocatalyst, as they offer the homogenous immobilization of metals within their ordered structure. Introducing Fe and Ni into the PHI network enables the formation of single and mixed transition metal PHIs, which show reduced overpotentials for ORR and OER. The formation of Ni single atoms even induces outstanding catalytic activity for the OER during charging of ZAB full cells with performance comparable to that of RuO2. Furthermore, full cell tests show excellent stability over the course of 250 discharge-charge cycles, making it a promising system for sustainable energy storage. This work paves the way for the molecular design of a novel material class as an electrocatalyst for ZAB.

Laboratory-based operando XAS on Li- and Na-ion batteries using the DANOISE cell demonstrated capabilities and limitations with von Hámos spectrometers.

Under the DAPHNE4NFDI consortium, RefXAS has evolved as a comprehensive open-access database for X-ray absorption spectroscopy (XAS). We have implemented a platform that allows users to submit raw datasets and associated metadata via a web interface. The database supports automated metadata handling and quality control, ensuring that uploaded data adheres to predefined standards. Recent developments include the integration of a standardised download package, improved filtering systems, and the transition to institutional data storage at DESY, alongside future plans to incorporate the NeXus format, enhancing machine learning applications. This paper provides an overview of these advancements and their implications for the XAS community.

While X-ray diffraction (XRD) is a commonly used method for quantification analysis using Rietveld refinement and quantitative Mössbauer spectroscopy is sporadically used primarily for iron speciation, laboratory X-ray Absorption Fine Structure Spectroscopy (lab-XAFS) is rarely applied for the quantitative determination of sample compositions. With the recent developments of laboratory-based XAFS spectrometers, this method becomes more interesting for many applications as well as for quantification. The goal of this study is to compare quantitative lab-XAFS via Linear Combination Fitting (LCF) of reference spectra with XRD and Mössbauer spectroscopy. Iron species analysis with the focus on the determination of the mass ratio alpha-iron(III) oxide (α-Fe2O3)/iron(II, III) oxide (Fe3O4) was used as an example. The examinations were performed on synthetic α-Fe2O3/Fe3O4 model mixtures and, predominantly, on a natural iron ore sample mainly consisting of the minerals hematite and magnetite, thus, these two iron oxides. For the iron K-edge lab-XAFS measurements an X-ray tube-based spectrometer using the von Hamos geometry with Highly Annealed Pyrolytic Graphite (HAPG) mosaic crystal optic was used. The capabilities and challenges of each method are discussed. The quantitative model mixtures examinations by lab-XAFS show results and accuracies similar to those obtained by XRD and Mössbauer spectroscopy. However, while the quantitative results for the iron ore investigations by lab-XAFS are in good agreement (deviation of 2 percent points) with the XRD results, the composition determined by Mössbauer spectroscopy differs clearly from the lab-XAFS and XRD results. Furthermore, the Mössbauer spectroscopic examinations hint the presence of an additional iron oxide species affecting the quantification. Besides the still common challenges in identification, differentiation and quantification of different iron oxides, the results show that quantitative lab-XAFS can particularly compete with quantitative XRD when determining the species composition of one element. This makes lab-XAFS particularly well-suited for routine analytics.

Due to their availability, low cost, and activity, cobalt-based catalysts are a promising alternative to platinum for the industrial propane dehydrogenation processes. However, their low stability due to sintering, phase transformation, and coke deposition leads to severe deactivation. In this work, the synthesis of amorphous, ordered mesoporous alumina with stabilized Co2+ nanoclusters (Co-m-Al2O3) via an evaporation-induced self-assembly synthesis route is presented. The ordered mesoporous alumina is characterized for containing a large amount of defective pentacoordinate Al3+ sites and a small amount of strong acid sites. The incorporation of Co2+ clusters within the m-Al2O3 structure enhances the dispersion and stability and preserves their reduction even after prolonged time on stream. This leads to a highly selective and steady catalytic performance in the propane dehydrogenation reaction under industrial-relevant conditions. A significantly low deactivation rate of 0.53 d(-1) with stable propylene selectivity of 95% is observed after 23 h, resulting in a 117% higher space-time yield toward propylene compared to the state-of-the-art impregnated Co/gamma-Al2O3 catalyst. Furthermore, Co-m-Al2O3 leads to 4.6 times less coke formation, measured in situ for the first time. The detailed study of the nature of the cobalt sites, together with the acidic properties of the alumina supports, provides a deeper understanding of cobalt-based catalysts for dehydrogenation reactions.

Confocal micro-X-ray fluorescence (micro-XRF) spectroscopy facilitates three-dimensional (3D) elemental imaging of heterogeneous samples in the micrometer range. Laboratory setups using X-ray tube excitation render the method accessible for diverse research fields but interpretation of results and quantification remain challenging. The attenuation of X-rays in composites depends on the photon energy as well as on the composition and density of the material. For confocal micro-XRF, attenuation severely impacts elemental distribution information, as the signal from deeper layers is distorted by superficial layers. Absorption correction and quantification of fluorescence measurements in heterogeneous composite samples have so far not been reported. Here, an absorption correction approach for confocal micro-XRF combining density information from microcomputed tomography (micro-CT) data with laboratory X-ray absorption spectroscopy (XAS) and synchrotron transmission measurements is presented. The energy dependency of the probing volume is considered during the correction. The methodology is demonstrated on a model composite sample consisting of a bovine tooth with a clinically used restoration material.

Under DAPHNE4NFDI, the X-ray absorption spectroscopy (XAS) reference database, RefXAS, has been set up. For this purpose, we developed a method to enable users to submit a raw dataset, with its associated metadata, via a dedicated website for inclusion in the database. Implementation of the database includes an upload of metadata to the scientific catalogue and an upload of files via object storage, with automated query capabilities through a web server and visualization of the data and files. Based on the mode of measurements, quality criteria have been formulated for the automated check of any uploaded data. In the present work, the significant metadata fields for reusability, as well as reproducibility of results (FAIR data principles), are discussed. Quality criteria for the data uploaded to the database have been formulated and assessed. Moreover, the usability and interoperability of available XAS data/file formats have been explored. The first version of the RefXAS database prototype is presented, which features a human verification procedure, currently being tested with a new user interface designed specifically for curators; a user-friendly landing page; a full list of datasets; advanced search capabilities; a streamlined upload process; and, finally, a server-side automatic authentication and (meta-) data storage via MongoDB, PostgreSQL and (data-) files via relevant APIs.

Solid solutions of Fe-doped ceria have been synthesized, characterized and applied as catalysts for tandem carbon dioxide hydrogenation.

High‐entropy spinel‐type oxides are synthesized by a modified Pechini process, wet chemistry approach, and solid‐state synthesis method and characterized as anode materials for Li‐ion batteries. The Pechini process that involves chelation and polyesterification reactions facilitates the formation of high‐entropy spinel‐type oxides without compositional segregation at ≈600 °C as confirmed by in situ and ex situ XRD. XAFS analysis and the Rietveld refinement of room‐temperature neutron diffraction data suggest the composition (Mn0.05Fe0.48Co0.47, tetrahedral)(Cr0.61Mn0.52Fe0.11Co0.09Ni0.68, octahedral)O4 for phase‐pure specimens. Compared to high‐entropy spinel‐type oxides synthesized by the solid‐state method, the precursor‐derived materials demonstrate higher specific capacity as anodes, in which the materials without citric acid addition exhibit low capacity fading at high current densities and maintained a capacity of ≈200 mAh g−1 after 1000 cycles. The generation of a rock‐salt‐type phase during cycling is confirmed for the first time by in situ charging–discharging XRD. The charging–discharging of this anode material is achieved mainly through the embedding–disembedding of lithium ions in the lattice of the generated rock‐salt‐type phase.

A group of (doped N or P) carbons were synthesized using soluble starch as a carbon precursor. Further, ceria nanoparticles (NPs) were confined into these (doped) carbon materials. The obtained solids were characterized by various techniques such as N2 physisorption, XRD, TEM, SEM, XPS, and XAS. These materials were used as catalysts for the oxidative coupling between benzyl alcohol and aniline as the model reaction. Ceria immobilized on mesoporous-doped carbon shows higher activity than the other materials, benchmark catalysts, and most of the previously reported catalysts. The control of the ceria NP size, the presence of Ce3+ cations, and an increment in the disorder in the ceria NP structure caused by a support-ceria interaction could increase the number of oxygen vacancies and improve its catalytic performance. CN-meso/CeO2 was also used as the catalyst for a rich scope of substrates, such as substituted aromatic alcohols, linear alcohols, and different types of amines. The influence of various reaction parameters (substrate content, reaction temperature, and catalyst content) on the activity of this catalyst was also checked.

X-ray absorption spectroscopy is important to analyse solid materials, in particular amorphous materials, disordered or multicomponent materials. Due to its vast application in diverse fields XAS has become an essential tool for studying, e.g., catalytic reactions or battery materials to mention just a few. In the field of XAS, data are often evaluated by comparing them to previously measured or calculated reference spectra [1]. This sets the high requirements concerning both spectral quality and documentation of the measurements. Under DAPHNE4NFDI, we have been working on to set up a XAS reference database including raw and processed data with an interface developed for uploading and evaluating the data. In this context, defining metadata fields about an XAS experiments and documenting this information along with data is essential to make the measured data reusable by any researcher in a similar field and beyond. Another important aspect of a curated database is that users should be able to easily judge the quality and the usability of each data set by looking at the mentioned quality criteria. In the present work, we have discussed and highlighted the importance of metadata fields and quality criteria for the data to be uploaded at the XAS database.

Electrochemical nitrate reduction to ammonia powered by renewable electricity is not only a promising alternative to the established energy-intense and non-ecofriendly Haber-Bosch reaction for ammonia generation but also a future contributor to the ever-more important denitrification schemes. Nevertheless, this reaction is still impeded by the lack of understanding for the underlying reaction mechanism on the molecular scale which is necessary for the rational design of active, selective, and stable electrocatalysts. Herein, a novel single-site bismuth catalyst (Bi-N-C) for nitrate electroreduction is reported to produce ammonia with maximum Faradaic efficiency of 88.7% and at a high rate of 1.38 mg h(-1) mg(cat)(-1) at -0.35 V versus reversible hydrogen electrode (RHE). The active center (described as BiN2C2) is uncovered by detailed structural analysis. Coupled density functional theory calculations are applied to analyze the reaction mechanism and potential rate-limiting steps for nitrate reduction based on the BiN2C2 model. The findings highlight the importance of model catalysts to utilize the potential of nitrate reduction as a new-generation nitrogen-management technology based on the construction of efficient active sites.

This paper presents the application of laboratory X-ray Absorption Fine Structure Spectroscopy (XAFS) in the field of iron coordination chemistry, especially for compounds with larger organic ligands and usually low contents of the metal.

Trace elements, functionalized nanoparticles and labeled entities can be localized with sub-mm spatial resolution by X-ray fluorescence imaging (XFI). Here, small animals are raster scanned with a pencil-like synchrotron beam of high energy and low divergence and the X-ray fluorescence is recorded with an energy-dispersive detector. The ability to first perform coarse scans to identify regions of interest, followed by a close-up with a sub-mm X-ray beam is desirable, because overall measurement time and X-ray dose absorbed by the (biological) specimen can thus be minimized. However, the size of X-ray beams at synchrotron beamlines is usually strongly dependent on the actual beamline setup and can only be adapted within specific pre-defined limits. Especially, large synchrotron beams are non-trivial to generate. Here, we present the concept of graphite-based, convex reflection optics for the one-dimensional enlargement of a 1 mm wide synchrotron beam by a factor of 5 to 10 within a 1 m distance. Four different optics are tested and characterized and their reflection properties compared to ray tracing simulations. The general shape and size of the measured reflection profiles agree with expectations. Enhancements with respect to homogeneity and efficiency can be expected with improved optics manufacturing. A mouse phantom is used for a proof-of-principle XFI experiment demonstrating the applicability of coarse and fine scans with the suggested optics design.

We report the synthesis of Ni/SiOCN ceramic nanocomposites with high surface area as catalysts for carbon dioxide and methane conversion.

In recent years, novel instrumentation for laboratory X-ray Absorption Spectroscopy (XAS) raised some interest and debate about its usefulness. Within the last two years then, a growing number of experiments and analytical applications using these new spectrometers were published. This review presents these applications and gives an overview of the fields of applications and the ways, the laboratory XAS instruments were utilized so far. The principles of the laboratory XAS spectrometer are described. The use of X-ray tube driven spectrometers for XAS, however, is not a novelty. First X-ray absorption spectra were taken long before synchrotron radiation facilities existed. And, more important for the scope of this review, beginning with the 80s, the XAS community undertook a considerable effort to create laboratory XAS spectrometers which were powerful enough for research in chemistry or materials science. The motivation of this effort as well as the application of laboratory XAS spectrometers have a lot in common with the current activities. We included a review of literature from this period and a discussion of commonalities and differences with contemporary