Lab News & Scientific Highlights

The results from the very first user experiment at SwissFEL have just been published in the Proceedings of the National Academy of Sciences (PNAS). The measurements probed the electron transport properties of the cytochrome c protein, which is found in cellular mitochondria. The measurements show that when the Fe atom at the centre of the protein undergoes electronic excitation, for example when it gains or loses and electron, the  active centre of the protein undergoes a doming structural rearrangement. This result raises interesting questions about how this structural change is involved in the electron transfer properties of cytochrome c.

A fundamental understanding of the active sites in technical CoMo/ Al₂O₃ catalysts is crucial to improve the production of clean transportation fuels by hydrodesulfurization (HDS), which removes sulfur from fossil fuels. Sulfur dioxide, resulting from fossil fuel combustion, is one of the main causes for acid rain. In situ X-ray spectroscopic experiments at the SuperXAS beamline of the SLS provided insight in the structure and number of active sites (“Co−Mo−S”) in sulfided CoMo/ Al₂O₃ catalysts. When the Co to Mo ratio is less than 0.1, cobalt forms isolated sites on the MoS₂ phase, where the cobalt promoter atoms are in centrosymmetric octahedral coordination with six-sulfur ligands.

Open shell organometallic bismuth are promising agents for catalytic applications, but difficult to characterize due to their high reactivity. The simplest methylbismuth (Bi-CH₃), a biradical species, was in-situ synthesized and spectroscopically characterized for the first time. Electronic and thermochemical properties could be obtained, which will guide future synthetic applications.

The nature of high activity of Cu/ZnO catalyst in methanol synthesis remains the subject of intensive debate. Here, the authors are revisiting carbon dioxide hydrogenation mechanism using high-pressure operando techniques.

Ultra-fast operando X-ray diffraction experiments reveal the temporal evolution of low and high temperature phases and the formation of residual stresses during laser 3D printing of a Ti-6Al-4V alloy. The profound influence of the length of the laser-scanning vector  on the evolving microstructure is revealed and elucidated.  

In this work, the complementarity of pump-probe experiments at SwissFEL (ALVRA endstation) and at synchrotrons (SuperXAS beamline of SLS and ID09 of ESRF) is used to investigate the triplet excited state of Cu OLED materials. Details about the charge transfer and structural rearrangements in the excited state of this material are revealed and obtained data can be used to verify computational methods for rational development of new OLED materials.

We monitored the dynamic structure of the active sites in a catalyst containing highly dispersed copper-oxo species on ceria during low-temperature CO oxidation using time-resolved X-ray absorption spectroscopy. We quantitatively demonstrate that the CO oxidation mechanism below 90 °C involves an oxygen intermediate strongly bound to the active sites as well as the redox activity of Cu²⁺/Cu⁺ and Ce⁴⁺/Ce³⁺ couples.

Unlike the homogeneous Wacker process, the understanding of the mechanism of the heterogeneous system has long remained to be superficial. Here the authors investigated the mechanism of heterogeneous Wacker oxidation over Pd-Cu/zeolite Y through transient XAS coupled with kinetic studies and chemometric analysis.

Small and narrowly distributed nanoparticles of copper alloyed with gallium supported on silica containing residual Ga^III sites can be obtained via surface organometallic chemistry. This material is highly active and selective for CO₂ hydrogenation to CH₃OH. In situ X-ray absorption spectroscopy shows that gallium is oxidized under reaction conditions while copper remains as Cu⁰.

Transition metals, characterized by their partially filled d-orbitals, provide the basis for many of the most relevant processes in chemistry, biology, and physics. Embedded as single atoms or in small clusters, they give rise to exceptional optical, chemical, and magnetic properties. So far, it has proven impossible to disentangle the complex network of excited quantum states, which greatly hinders predicting and controlling of material properties. We employed double-resonant four-wave mixing spectroscopy to quantitatively resolve the bright and perturbing dark quantum states of the neutral copper dimer.

In the week of April 1-5 PSI welcomes 20 PhD students and postdocs taking part in the European HERCULES 2019 school on Neutron and Synchrotron Radiation. They will attend lectures and perform two days of practical courses at several beam lines of the Swiss Light Source.

Lithium ion batteries (LIB) are essential in modern everyday life, with increasing interest in enhancing their performance and lifetime. Secondary particles of Li-rich cathode material were examined with correlated ptychographic X-ray tomography and diffraction microscopy at different stages of cycling to probe the aging mechanism.

Light alkanes are abundantly available and cheap resources that are often burned at oil wells because of the missing infrastructure for valorization. Novel technologies are needed for their selective functionalization to use natural gas as an energy vector in the transition between the oil and the renewables era. Catalytic oxyhalogenation may unlock the transformation of cheap and abundant alkanes into commodities. When chlorine-based reactions are compared with bromine, improved selectivities above an iron catalyst arise from surface-confinement of the reaction mechanism in the case of chlorine as halogen.

To date the electrochemical activity of battery materials was always relying in the oxidation/reduction of cationic redox (change of oxidation state of transition metals generally). However, recently, it was established in new cathode materials (so call Li-rich cathode) that the oxygen from the crystal lattice might also play the role of anionic redox center leading to enhance then the specific charge of battery materials.

The high brilliance of new X-ray sources such as X-ray Free Electron Laser opens the way to non-linear spectroscopies. These techniques can probe ultrafast matter dynamics that would otherwise be inaccessible. One of these techniques, Transient Grating, involves the creation of a transient excitation grating by crossing X-ray beams on the sample. Scientists at PSI have realized a demonstration of such crossing by using an innovative approach well suited for the hard X-ray regime.

The link between Pd nanoparticle structure and surface reactivity for NH3 abatement was found using operando X-ray absorption fine structure spectroscopy, diffuse reflectance infrared Fourier-transformed spectroscopy and on-line mass spectrometry.

This work presents a new approach for synthesizing Fe-based oxygen reduction reaction (ORR) catalysts using sodium carbonate (Na₂CO₃) as an inexpensive but effective pore-inducing agent offering microporosity control.

A major milestone in the commissioning of SwissFEL has been reached: the first pump-probe experiments on proteins have been successfully carried out. Crystals of several retinal-binding proteins were delivered in a viscous jet system and a femtosecond laser was used to start the isomerization reaction. Microsecond to sub-picosecond snapshots were then collected, catching the retinal proteins shortly after isomerization of the chromophore.

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.

On the 7th to 12th of August 2018, a collaborative group of scientists from the Paul Scherrer Institute and members of the LeadXpro and Heptares pharmaceutical companies led by Karol Nass (PSI macromolecular crystallography MX-SLS group) performed the first serial femtosecond crystallography (SFX) pilot user experiment at the SwissFEL X-ray free electron laser (XFEL).

The different reaction steps involved in repeated Pt13In9 segregation‐alloying are identified by XAS and kinetically characterized at the single‐cycle level.

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.

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.

Using targeted synthesis and in situ characterization a palladium catalyst with improved stability against sintering during methane oxidation was prepared.

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.

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.

Dynamic Structural Changes of Active Sites in Pt–Ni Bimetallic Catalysts Revealed by a Multimodal Approach

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 Light Source.