30 October 2018
Studying organic molecular magnets is a challenge, because the high-spin diradical character of these compounds dramatically increases the reactivity and reduces the lifetime. Researchers from PSI, ETH Zurich, Wollongong and Melbourne, Australia succeeded in taming the meta-xylylene diradical and were able to study its electronic and thermochemical properties.
28 September 2018
Carbonate minerals serve as reservoir for CO2 in the global CO2 cycle, as biomineral in animal skeletons and shells of marine animals, and are used in carbon capturing techniques. Moreover, they serve as an important model system in crystallization studies, and have important commercial applications, for example as fillers. Researchers from EPFL and PSI developed a new methodology to study the crystallization of CaCO3 that offers both high temporal and spatial resolution, which is the key challenge in elucidating early stages of crystallization. Using X-ray absorption spectroscopy and other techniques it could be demonstrated that the degree of hydration of amorphous CaCO3 increases during its growth. As a result of the increasing degree of hydration, the stability of the resulting amorphous particles against solid-state crystallization decreases.
15 August 2018
Single atomic layers of aluminum oxide embedded in SiO2 thin films, play an important role for the design of carrier-selective passivating contacts for high efficiency silicon based photovoltaic applications. Researchers from the Australian National University (ANU, Canberra, Australia), the Karlsruhe Institute of Technology (IT, Karlsruhe, Germany) and PSI have used synchrotron radiation to reveal the bonding configuration and local atomic surrounding of the Al-atoms in such surface oxide layers. The results corroborates theoretical calculations and contribute to a new model to explain the origin of the negative fixed charge in the Al-O/SiO2 stack, which has promising properties for a carrier-selective passivating contact for future silicon solar cells.
1 August 2018
The different reaction steps involved in repeated Pt13In9 segregation‐alloying are identified by XAS and kinetically characterized at the single‐cycle level.
28 July 2018
The highest award of the international X-ray absorption spectroscopy (IXAS) society, the Edward Stern Outstanding Achievement Award, was presented to Prof. Ronald Frahm during the tri-annual IXAS meeting in Kraków, Poland in July 2018.
15 July 2018
The mechanism of hydrogen evolution by cobalt polypyridyls catalysts is investigated. Pump-probe X‐ray absorption spectra measured at SuperXAS in the microsecond time range indicate that the pendant pyridine dissociates from the cobalt in the intermediate Co(I) state. This opens the possibility for pyridinium to act as an intramolecular proton donor, which can be used for the development of efficient catalysts.
29 June 2018
Using targeted synthesis and in situ characterization a palladium catalyst with improved stability against sintering during methane oxidation was prepared.
19 June 2018
In the last two decades, small-angle X-ray scattering (SAXS) and X-ray absorption spectroscopy (XAS) have evolved into two well-established techniques capable of providing complementary and operando information about a sample’s morphology and composition, respectively. Considering that operation conditions can often lead to simultaneous and related changes in a catalyst’s speciation and shape, herein we introduce a setup that combines SAXS and XAS in a configuration that allows optimum acquisition and corresponding data quality for both techniques.
1 June 2018
Catalytic oxybromination may turn the cheap and abundant feedstock methane into the platform compounds bromomethane and dibromomethane. Yet researchers have been puzzled by the catalysis mechanism, which was speculated to involve free radical intermediates. Operando photoelectron photoion coincidence helped distinguish surface and gas-phase reaction steps and elucidated the crucial halogen-mediated C–H bond activation step, which is driven by elusive bromine and methyl radicals.
2 April 2018
Subnanometer bimetallic catalyst exhibit unique atomic structures and resulting catalytic properties, in particular enhanced activities and improved selectivities. Determining the dynamic atomic structures developing in heterogeneously supported forms under reaction conditions is key to identify their active sites.
Based on an advanced multimodal analytical approach - including in situ
X-ray Absorption Spectroscopy (XAS), Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and ex-situ aberration corrected Scanning Transmission Electron Microscopy (STEM) - complex reactions occurring between the bimetallic nanoclusters and the support have been documented under operando conditions. Bimetallic nanoparticles possessing an intermetallic structure that are conjoined with Ni-rich, metal-silicate substrate species are identified as the active phase.
20 March 2018
Claystones and cement-based materials are key materials for safe disposal of radioactive waste in deep geological repositories. In Switzerland, Opalinus Clay, was selected as geological host material. At the Mont Terri rock laboratory the alteration of cement in contact with the natural clay is studied in a several years lasting experiment. The formation of different magnesium containing phases at the interface was studied using X-ray absorption micro-spectroscopy at the PHOENIX beamline of the Swiss Light Source (SLS).
19 March 2018
In the week of March 18-23 PSI welcomes 20 PhD students and postdocs taking part in
the HERCULES 2018 school on Neutron and Synchrotron Radiation. They will attend
lectures and perform two days of practical courses at several beam lines of the Swiss
8 March 2018
Through the combination of time-resolved X-ray absorption spectroscopy and transient experimentation, we were able to capture an ammonia inhibition effect on the rate-limiting copper re-oxidation at low temperature.
27 February 2018
Classical theory predicts that supersaturated carbonate solutions consist mostly of ions and ion pairs, with a small number of larger clusters present in the solution. The population of the different sized clusters in a solution is solely defined by the cluster’s size dependent Free Energy. If clusters are large enough they serve as nucleation germs for a new solid phase. The nucleation occurs once the surface free energy barrier posed by the new solid-liquid interface is overcome by the free energy win from bulk phase growth. However, for calcium carbonate solutions, this classical view has been challenged by the emergence of non-classical theories. In a novel experiment, using synchroton X-ray absorption spectroscopy, the molecular structure around the solvated calcium ion in dilute supersaturated calcium carbonate solutions was probed in situ. The results obtained definitively show that supersaturated calcium carbonate solutions are dominated by ions and ion pairs. The presence of larger oligomers as predicted by non-classical theories was not detected. Moreover, predictions from independent theoretical calculations on the structure of supersaturated calcium carbonate solutions were in congruence with the experimental results. As a consequence, it is quite clear that the nucleation of calcium carbonate follows a classical pathway.
2 February 2018
Sulfate in biogenic carbonates is an important proxy for reconstructing the marine sulfur cycle. To investigate the exact location of carbonate associated sulfate (CAS) in biogenic carbonates and the effects of diagenetic alteration on sulfur in carbonates, shells of the marine bivalve Arctica islandica were artificially altered in modified seawater. Sulfur XANES analyses showed that CAS in A. islandica is indeed incorporated into the mineral part of the pristine shell, most likely as a hydrated or partly hydrated sulfate phase. The multi-analytical approach of XANES and µ-XRF analyses, sulfur isotope measurements, NanoSIMS analyses, and microstructural analysis on thin-sections of the shell samples further revealed that the different sulfur in a bivalve shell sensitively reacts to artificially induced hydrothermal alteration.
29 January 2018
Using a unique set of well-defined silica-supported Ni nanoclusters (1–7 nm) and advanced characterization methods it was proved how structure sensitivity influences the mechanism of catalytic CO2 reduction, the nature of which has been long debated.
6 October 2017
Al T-sites are of crucial importance for the function of zeolite catalysts. These T-sites, which serve as Brønsted acid reaction centers, interact strongly with water. The location of these T-sites and their chemical state in the presence of water were elucidated using x-ray absorption spectroscopy (XAS) at the PHOENIX beamline at the Swiss Light Source of the PSI.
8 August 2017
Unique insights into the adolescence and metabolism of a Malaria parasite in a human red blood cell are obtained by a new chemical imaging methodology – in situ
correlative X-ray fluorescence microscopy and soft X-ray tomography.
17 July 2017
By combining a scalable cutting-edge synthesis method with time-resolved X-ray absorption spectroscopy measurements, it was possible to capture the dynamic local electronic and geometric structure during realistic operando conditions for highly active OER perovskite nanocatalysts.
13 July 2017
Lignin is a major constituent of plants, and may be used as a precursor for fuels and fine chemicals. Catalytic fast pyrolysis of lignin is one of the most promising approaches. By using vacuum ultraviolet synchrotron radiation and threshold photoelectron spectroscopy we could identify elusive intermediates, which are responsible for the formation of phenol and benzene and could thus tackle this reaction mechanism. Mechanistic understanding could enable targeted improvement of production methods in the future, beyond the currently used "cook-and-look" approach.
31 May 2017
Online combustion analysis relies heavily on spectral data to detect reactive intermediates isomer-selectively to establish e.g. kinetic flame models. Due to the difficulty to generate these species cleanly, spectral data are rather scarce. Here we report on the selective generation of three picolyl radical isomers (C5
*) by deamination of aminomethylpyridines. Picolyl radicals are relevant in biofuel combustion, and could now be characterized by threshold photoelectron spectroscopy using synchrotron radiation. Vibrationally resolved bands and distinct ionization energies allow for isomer-specific detection of these elusive species in complex environments and permit us to explore new avenues in soot- and NOx formation kinetics.
30 May 2017
Natural geological and engineered barriers play a key role in protecting the environment and the anthroposphere from the hazardous impact of deposited waste or spreading contaminants. Such natural geological and engineered barrier materials are commonly complex and heterogeneous. In-situ multimodal microscopic studies under conditions relevant to deep geological formations are crucial to identify the reactive components and reaction pathways or to validate proposed immobilization mechanisms. The present study demonstrated that a simplistic description by a sole reactive component is not an adequate representation of the geochemical reactivity responsible for the immobilization of plutonium within a natural Clay Rock barrier. Multimodal chemical imaging studies on intact, undisturbed systems are absolutely essential to ascertain the geochemical reactivity for relevant geochemical conditions and settings.
5 May 2017
On the basis of in situ x-ray absorption spectroscopy, infrared spectroscopy, and density functional theory calculations, it was proposed a mechanism involving methane oxidation at Cu II oxide active centers, followed by Cu I reoxidation by water with concurrent formation of hydrogen.
26 April 2017
The superior performance of molecularly tailored methane dry reforming catalyst resulted in a maximization of the amount of accessible metallic nickel in the form of small nanoparticles preventing coke deposition. Operando X-ray absorption near-edge structure spectroscopy confirms that deactivation largely occurs through the migration of Ni into the support.
21 March 2017
Ru-based perovskites, i.e. SrRuO3 and LaRuO3, have been predicted as active perovskites to exhibit a particularly high oxygen evolution reaction activity. We highlight that understanding the origin of stability under a real operating environment is absolutely essential for the design of a sustainable electrocatalyst with optimal balance between activity and stability.
17 February 2017
We have developed a synthetic approach to highsurface-area chlorine-free iridium oxide nanoparticles dispersed in titania (IrO2-TiO2), which is a highly active and stable OER catalyst in acidic media. Operando X-ray absorption studies demonstrate the evolution of the surface species as a function of the applied potential, suggesting the conversion of the initial hydroxo surface layer to the oxo-terminated surface via anodic oxidation.
24 November 2016
Highly active phases in carbon monoxide oxidation are known, however they are transient in nature. Here, we determined for the first time the structure of such a highly active phase on platinum nanoparticles in an actual reactor.
1 November 2016
The false coincidence background has so far limited the analytical application of PEPICO, photoelectron photoion coincidence.
A new photoioin rastering technique has been developed to separate the wheat from the chaff and identify true coincidences based on the ion hit time and position.
This expands the dynamic range of the experiment by at least two orders of magnitude, allowing for novel applications to look for reactive intermediates and short
lived species in reaction environments.
21 October 2016
The activation and conversion of hydrocarbons is one of the most important challenges in chemistry. This work shows that isolated Co(II) sites are catalysts for a number of hydrocarbon conversion reactions, such as the dehydrogenation of propane, the hydrogenation of propene, and the trimerization of terminal alkynes. The data are consistent with all of these reactions occurring by a common mechanism, involving heterolytic C–H or H–H activation via a 1,2 addition across a Co–O bond.
4 October 2016
The kinetics involved in novel ambient-temperature mechanism for the catalytic oxidation of carbon monoxide by oxygen over a Pt/Al2O3 catalyst is evaluated within a periodic redox operation paradigm using combined mass spectrometry (MS), diffuse reflectance infrared spectroscopy (DRIFTS), and time-resolved Pt L3-edge XAFS. A high-wavenumber (ca. 1690 cm-1) carbonate species are shown to be associated with a room-temperature redox process occurring in a fraction of the Pt atoms present in the catalyst.
13 September 2016
The advent of X-ray free electron lasers (XFELs) is opening the ability to reach extremely high photon numbers within ultrashort X-ray pulse durations and is leading to a paradigm shift in our ability to explore nonlinear X-ray signals.
29 August 2016
A simple and scalable method for preparation of well-defined chlorine–free iridium oxide nanoparticles active for oxygen evolution reaction (OER) was developed. Operando X-ray absorption spectroscopy and X-ray photoelectron spectroscopy indicate that OER activity is strongly related to the presence of iridium hydroxo (Ir–OH) species on the surface of iridium oxide nanoparticles.
26 August 2016
An interdisciplinary study conducted at different PSI laboratories (LES
) in collaboration with Studsvik AB (Sweden) demonstrates that selenium originating from fission in light water reactors is tightly bound in the crystal lattice of UO2. This finding has positive consequences for the safety assessment of high-level radioactive waste repository planned in Switzerland, as it implies (contrary to previous assumptions) that the safety-relevant radionuclide 79Se will be released at extremely low rates during aqueous corrosion of the waste in a deep-seated repository.
By Enzo Curti (PSI-LES)
4 August 2016
Industrial alkene metathesis processes rely on silica-supported tungsten oxide catalysts, which operate at high temperatures (>350 °C) due to the difficulty in generating active sites (carbenes or metallacyclobutanes). We report here a low temperature activation process of well-defined metal oxo surface species using organosilicon reductants, which generate a large amount of active species at only 70 °C (0.6 active sites/W).
11 April 2016
The diet in many developing countries is lacking zinc, but researchers have just solved the riddle of how to get more zinc into crop seeds. The discovery has been published in Nature Plants, and the research was led by University of Copenhagen.
By Johanne Uhrenholt Kusnitzoff
30 March 2016
In order to understand limitations in current battery materials and systematically engineer better ones, it is helpful to be able to directly visualize the lithium dynamics in materials during battery charge and discharge. Researchers at ETH Zurich and Paul Scherrer Institute have demonstrated a way to do this.
7 March 2016
Using an assembly of colloidal nanocrystals a Ag-PbS nanocomposite was produced with increased thermoelectic figures of merit up to 1.7K at 850 K. EXAFS spectroscopy at the Ag K-edge was essential to show that Ag does not dissolve in PbS nanoparticles but preserved the individual nanodomains. This reduces the PbS intergrain energy barriers for charge transport