News & Scientific Highlights

A deep understanding of active site architectures during surface-catalyzed reactions is a crucial step for the design of recyclable heterogeneous catalysts for organic synthesis. In this work, a droplet-based microfluidic setup was developed and applied to perform Suzuki-Miyaura coupling over heterogenous single-atom Pd-catalyst. 

Here we use in-situ high-temperature x-ray absorption spectroscopy (XAS) and theoretical calculations to quantify the amorphous structure of bulk and nanoscale GeTe. Based on XAS experiments, we develop a theoretical model of the amorphous GeTe structure, consisting of a disordered fcc-type Te sublattice and randomly arranged chains of Ge atoms in a tetrahedral coordination.

Pt-FeO_x(OH)_y interface with enhanced activity for PROX is generated via strong metal-support interaction. Increase in the degree of hydroxylation of Pt-FeO_x(OH)_y interface enhances the rate of PROX mediated by active Fe²⁺ species.

Carbon supports are ubiquitous components of heterogeneous catalysts for acetylene hydrochlorination to vinyl chloride, from commercial mercury-based systems to more sustainable metal single-atom alternatives. Their potential co-catalytic role has long been postulated but never unequivocally demonstrated. Herein, combining operando X-ray absorption spectroscopy with other spectroscopic and kinetic analyses, we evidence the bifunctionality of carbons and metal sites (Pt, Au, Ru) in the acetylene hydrochlorination catalytic cycle.

Zirconium-containing metal-organic framework (MOF) with UiO-66 topology is an extremely versatile material, which finds applications beyond gas separation and catalysis.  By means of in situ time-resolved high-resolution mass spectrometry, Zr K-edge X-ray absorption spectroscopy, magic-angle spinning nuclear magnetic resonance spectroscopy, and X-ray diffraction it is showed that the nucleation of UiO-66 occurs via a solution-mediated hydrolysis of zirconium chloroterephthalates, whose formation appears to be autocatalytic.

Using operando time-resolved X-ray absorption spectroscopy, we investigated the origin of volcano-shaped ethanol oxidative dehydrogenation activity trend of VOx/CeO2 catalysts as a function of VOx surface coverage. Vanadium and cerium synergistically change their oxidation states during the catalytic cycle. The catalytic activity correlates with the concentration of reversible Ce4+/3+species.

The ability to study in situ the formation and consumption of Pd hydrides (PdH) in liquid environments is a significant challenge hampering a deeper understanding of catalyzed liquid-phase hydrogenation reactions. Here, using quick scanning X-ray absorption spectroscopy (QEXAFS), we present a detailed kinetic study of Pd hydride formation and reactivity on Pd/Al₂O₃ in 2-propanol solvent. 

Operando/in situ spectro-electrochemical studies often require high loadings and thick catalyst layers (CLs) leading to large ion- and mass-transport limitations. In this study we investigate PdH-formation in two Pd-catalysts with similar surface areas but drastically different morphologies. Our results unveil that the CL-thickness largely determines the PdH formation trends calling for the minimization of the CL-thickness in such experiments.

Operando X-ray absorption spectroscopy revealed a linear correlation between the amount of oxidic Fe²⁺ and the ambient temperature activity of Pt−FeO_x preferential carbon monoxide oxidation catalysts. The hydrogen prereduction temperature and pressure determines the amount of active Fe²⁺ sites for alumina- and silica-supported Pt−Fe catalysts. Catalyst deactivation is linked with the oxidation of these sites.

The development of next-generation perovskite-based optoelectronic devices relies critically on the understanding of the interaction between charge carriers and the polar lattice in out-of-equilibrium conditions. While it has become increasingly evident for CsPbBr₃ perovskites that the Pb–Br framework flexibility plays a key role in their light-activated functionality, the corresponding local structural rearrangement has not yet been unambiguously identified. In this work the photoinduced lattice changes were investigated using combination of time-resolved and temperature-dependent studies at Br K and Pb L₃ X-ray absorption edges and ab initio simulations.

Operando time-resolved V and Ti K-edge X-ray absorption near-edge spectroscopy, coupled with a transient experimental strategy, quantitatively showed that the formation of acetaldehyde over 5% V₂O₅/15% TiO₂/SiO₂ is kinetically coupled to the formation of a V⁴⁺ intermediate, while the formation of V³⁺ is delayed and 10–70 times slower. The low-coordinated nature of various redox states of VO_x species (V⁵⁺, V⁴⁺, and V³⁺) in the 5% V₂O₅/15% TiO₂/SiO₂ catalyst is confirmed using the extensive database of V K-edge XANES spectra of standards and specially synthesized molecular crystals.

Cu diimine complexes present a noble metal free alternative to classical Ru, Re, Ir and Pt based photosensitizers in solution photochemistry, photoelectrochemical or dye-sensitized solar cells. Optimization of these dyes requires an understanding of factors governing the key photochemical properties: excited state lifetime and emission quantum yield. Using pump-probe XAS and DFT calculations we have explored the involvement of exciplex formation in the deactivation of the photoexcited state.

Platinum chloride in aqueous solution promotes the dispersion of large gold nanoparticles (>70 nm) on carbon carriers into single atoms, forming bimetallic single-atom catalysts with improved resistance against sintering at temperatures up to 800 K and under the harsh reductive reaction conditions of acetylene hydrochlorination, leading to improved lifetime in this reaction. To rationalize these observations, this study, led by ETH Zurich, utilized X-ray adsorption spectroscopy conducted at the SuperXAS beamline of the SLS to provide insights into the degree of gold dispersion and the structure of the isolated metal sites in the bimetallic catalysts.

Ni-Fe oxyhydroxide is among the most active oxygen evolution electrocatalysts. Electrolyte alkali metal cations modify the activity and reaction intermediates, however, the exact mechanism is at question due to unexplained deviations from the cation size trend. Our X-ray absorption spectroelectrochemical results show that the OER activity follows the variations in .electrolyte pH rather than a specific cation. Our DFT-based reactivity descriptors confirm the conclusions of an indirect pH effect.

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.

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.

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.

In order to clarify the mechanism behind this activity loss, in this study two high surface area iridium oxides were characterized under operando conditions using a novel setup that allows the quasi-simultaneous acquisition of anomalous small angle X-ray scattering (A-SAXS) and X-ray absorption spectroscopy (XAS) data.

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.

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.

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.