Jakub Szlachetko

A von Hamos x-ray spectrometer based on a segmented-type diffraction crystal for single-shot x-ray emission spectroscopy and time-resolved resonant inelastic x-ray scattering studies

We report on the design and performance of a wavelength-dispersive type spectrometer based on the von Hamos geometry. The spectrometer is equipped with a segmented-type crystal for x-ray diffraction and provides an energy resolution in the order of 0.25 eV and 1 eV over an energy range of 8000 eV-9600 eV. The use of a segmented crystal results in a simple and straightforward crystal preparation that allows to preserve the spectrometer resolution and spectrometer efficiency. Application of the spectrometer for time-resolved resonant inelastic x-ray scattering and single-shot x-ray emission spectroscopy is demonstrated.

Catalytically Active and Spectator Ce3+ in Ceria-Supported Metal Catalysts†

Identification of active species and the rate-determining reaction steps are crucial for optimizing the performance of oxygen-storage materials, which play an important role in catalysts lowering automotive emissions, as electrode materials for fuel cells, and as antioxidants in biomedicine. We demonstrated that active Ce(3+) species in a ceria-supported platinum catalyst during CO oxidation are short-lived and therefore cannot be observed under steady-state conditions. Using time-resolved resonant X-ray emission spectroscopy, we quantitatively correlated the initial rate of Ce(3+) formation under transient conditions to the overall rate of CO oxidation under steady-state conditions and showed that ceria reduction is a kinetically relevant step in CO oxidation, whereas a fraction of Ce(3+) was present as spectators. This approach can be applied to various catalytic processes involving oxygen-storage materials and reducible oxides to distinguish between redox and nonredox catalytic mechanisms.

High energy resolution off-resonant spectroscopy at sub-second time resolution: (Pt(acac)2) decomposition.

We report on the decomposition of platinum acetylacetonate (Pt(acac)(2)) in hydrogen induced by flash heating. The changes in the local Pt structure were followed by high energy resolution off-resonant spectroscopy uniquely performed with sub-second time resolution. The decomposition consists of a two-step reduction process of the Pt(II) species.

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.

Wavelength-dispersive spectrometer for X-ray microfluorescence analysis at the X-ray microscopy beamline ID21 (ESRF)

A polycapillary-based wavelength-dispersive spectrometer is reported. The design consideration as well as operation characteristics are presented.

Subsecond and in Situ Chemical Speciation of Pt/Al2O3 during Oxidation Reduction Cycles Monitored by High-Energy Resolution Off-Resonant X-ray Spectroscopy

We report an in situ time-resolved high-energy resolution off-resonant spectroscopy study with subsecond resolution providing insight into the oxidation and reduction steps of a Pt catalyst during CO oxidation. The study shows that the slow oxidation step is composed of two characteristic stages, namely, dissociative adsorption of oxygen followed by partial oxidation of Pt subsurface. By comparing the experimental spectra with theoretical calculations, we found that the intermediate chemisorbed O on Pt is adsorbed on atop position, which suggests surface poisoning by CO or surface reconstruction.

Synthesizing lead antimonate in ancient and modern opaque glass

Through the study of lead antimonate based opacifiers in three opaque glass productions—Egyptian glass of the 18th dynasty (1570–1292 BC), Roman mosaic tesserae and beads from Aquilea and Rome (2nd c. BC–5th c. AD) and Nevers lampworking glass figures 18th c. AD)—this paper shows the evolution of lead antimonate production during different periods of History. We also show the necessity of using systematic micro-chemical analyses, with both high spatial and high energy resolution techniques to investigate these types of materials. The synchrotron-based μ-XANES measurements combined with the microstructure observations (SEM and TEM), the chemical and structural analyses (EDX, WDS, μ-Raman), is the first step to getting information on the raw materials used and the technological processes employed to produce lead antimonate. The heterogeneity from one sample to another but also within the same sample, and even further within a single crystal aggregate clearly shows that a production cannot be unambiguously associated to a single chemical composition. However, differences between the three productions are clearly highlighted and hypotheses about glass manufacturing are proposed.

AuI Catalysis on a Coordination Polymer: A Solid Porous Ligand with Free Phosphine Sites

Heterogeneous catalysts are extremely important for the chemical industry. They are employed in the most important processes, which range from bulk to fine-chemical synthesis, because they present major economical and practical advantages, such as easy catalyst separation and recycling. Traditional heterogeneous catalysts are mainly constituted from metal particles that are deposited onto an oxide support, but, more often than not, only a few percent of the metal acts as the “real” active site, whereas the remaining majority is a spectator species. For this reason, the design of traditional heterogeneous catalysts on the atomic level for selective processes is quite difficult. On the other hand, homogeneous catalysts are well-defined and allow fine-tuning of the electronic and steric properties of the catalyst, thereby increasing the efficiency and selectivity of this process. However, their recycling and separation from the reaction mixture is expensive and presents more than a few engineering issues. Many researchers have tried to combine the separation and recycling properties of heterogeneous catalysts with the ability to have well-defined single sites, as in homogeneous catalysts. One such strategy is to develop a material that allows the facile coordination of single sites by designing a homogeneous-like catalyst on a solid support. However, few materials have the ability to coordinate single atoms without sintering, which is one of the main reasons why this chemistry is still at such an early stage. To overcome this problem, materials that are functionalized with atoms that are able to form relatively strong bonds with transition metals, with retention in a confined space, are required. Such materials, which are termed solid porous ligands (SPL), are normally quite difficult to obtain, owing to the limited chemical reactions that are known for standard solid supports. Following the discovery of coordination polymers (CPs), that is, materials that are constituted from a combination of multidentate organic building blocks with inorganic units, and their derivatives with a defined metal–organic framework (MOF) structure, new perspectives for the synthesis of functional solids that are able to coordinate single atoms through post-synthetic modification (PSM) have been reported. Nowadays, CPs that contain functionalities such as amino, alcohol, and imidazolium salts exist, but their synthesis is often not straightforward and their applications are limited. Surprisingly, materials with free organophosphorus functionalization are extremely rare, even though phosphines are among the most widely employed ligands in industrial homogeneous catalysis. Herein, we report the synthesis, characterization, and catalytic application of a new highly microporous P-functionalized CP that allows the coordination of single metal atoms (in this case, Au). This material was applied in catalysis by employing experimental and theoretical concepts that were developed in homogeneous catalysis. Very high metal loading was achieved. The concept and ability to heterogenize homogeneous catalysts that are based on phosphine SPLs at high weight loading opens up many new opportunities for the further application of coordination polymers and metal–organic frameworks as catalysts. Our design of a P-functionalized coordination polymer began by choosing an appropriate organic linker and inorganic unit ; as an organic building block, we selected 4,4’,4’’-phosphinetriyltribenzoic acid (H3ptba; Figure 1), owing to its facile synthesis from commercially available tris(4-methylphenyl)phosphine. Our metal of choice was zirconium because: 1) it has a low affinity with phosphine ligands and, therefore, the coordination of the P atom of H3ptba to it is minimized; and 2) it can form highly stable MOFs, such as UiO-66. An initial synthesis screen was performed under analogous conditions to those used for the production of UiO-66, which afforded an amorphous material (see the Supporting Information, Figure S1a) with a relatively low surface area (414 mg ). Because the addition of an acid, such as benzoic and acetic acid, in the synthesis of the UiO-66 series increased the size and surface area of the crystallites, we performed the synthesis in the presence of acetic acid (150 equiv; Figure 1, step 1). Under such conditions, the PXRD pattern of the product showed a crystalline material that featured several reflections of 2q between 38 and 408 (see the Supporting Information, Figure S1b). This compound was named LSK-1, in which LSK represents the German acronym of the Laboratory for Catalysis and Sustainable Chemistry at the Paul Scherrer Institute. [a] M. Servalli, Dr. J. Szlachetko, Dr. M. Ranocchiari, Prof. J. A. van Bokhoven Laboratory of Catalysis and Sustainable Chemistry Paul Scherrer Institute CH-5232, Villigen PSI (Switzerland) E-mail : jeroen.vanbokhoven@chem.ethz.ch marco.ranocchiari@psi.ch [b] J. V clav k, Dr. C. Lothsch tz, Prof. J. A. van Bokhoven Department of Chemistry and Applied Biosciences Laboratory of Chemical and Bioengineering ETH Zurich, CH-8093, Z rich (Switzerland) [c] Dr. J. Szlachetko Institute of Physics University of Kielce 25-314 Kielce (Poland) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201200844.

Photopolymerized polypyrrole microvessels.

We report on the preparation of water-filled polymer microvessels through the photopolymerization of pyrrole in a water/chloroform emulsion. The resulting structures were characterized by complementary spectroscopic and microscopic techniques, including Raman spectroscopy, XPS, SEM, and TEM. The encapsulation of fluorescent, magnetic, and ionic species within the microvessels has been demonstrated. Confocal microscopy and fluorescence anisotropy measurements revealed that the encapsulated chromophore (Rhodamine 6G) resides within voids in the capsules; however, strong interaction of the dye with polypyrrole results in a measurable decrease in its rotational dynamics. Microvessels loaded with ferrofluid exhibit magnetic properties, and their structures can be directed with an external magnetic field. TEM measurements allowed imaging of individual nanoparticles entrapped within the vessels. The application of Cu(2+)-loaded microvessels as a transducer layer in all-solid-state ion-selective electrodes was also demonstrated.

Communication: The electronic structure of matter probed with a single femtosecond hard x-ray pulse

Physical, biological, and chemical transformations are initiated by changes in the electronic configuration of the species involved. These electronic changes occur on the timescales of attoseconds (10−18 s) to femtoseconds (10−15 s) and drive all subsequent electronic reorganization as the system moves to a new equilibrium or quasi-equilibrium state. The ability to detect the dynamics of these electronic changes is crucial for understanding the potential energy surfaces upon which chemical and biological reactions take place. Here, we report on the determination of the electronic structure of matter using a single self-seeded femtosecond x-ray pulse from the Linac Coherent Light Source hard x-ray free electron laser. By measuring the high energy resolution off-resonant spectrum (HEROS), we were able to obtain information about the electronic density of states with a single femtosecond x-ray pulse. We show that the unoccupied electronic states of the scattering atom may be determined on a shot-to-shot basis and that the measured spectral shape is independent of the large intensity fluctuations of the incoming x-ray beam. Moreover, we demonstrate the chemical sensitivity and single-shot capability and limitations of HEROS, which enables the technique to track the electronic structural dynamics in matter on femtosecond time scales, making it an ideal probe technique for time-resolved X-ray experiments.