Ramona Thalinger

Exsolution of Fe and SrO Nanorods and Nanoparticles from Lanthanum Strontium Ferrite La0.6Sr0.4FeO3−δ Materials by Hydrogen Reduction

Formation of uniform Fe and SrO rods as well as nanoparticles following controlled reduction of La0.6Sr0.4FeO3−δ (LSF) and Ni-LSF samples in dry and moist hydrogen is studied by aberration-corrected electron microscopy. Metallic Fe and SrO precipitate from the perovskite lattice as rods of several tenths of nm and thicknesses up to 20 nm. Based on a model of Fe whisker growth following reduction of pure iron oxides, Fe rod exsolution from LSF proceeds via rate-limiting lattice oxygen removal. This favors the formation of single iron metal nuclei at the perovskite surface, subsequently growing as isolated rods. The latter is only possible upon efficient removal of reduction-induced water and, subsequently, reduction of Fe +III/+IV to Fe(0). If water remains in the system, no reduction or rod formation occurs. In contrast, formation of SrO rods following reduction in dry hydrogen is a catalytic process aided by Ni particles. It bears significant resemblance to surface diffusion-controlled carbon whisker growth on Ni, leading to similar extrusion rods and filaments. In addition to SrO rod growth, the exsolution of Fe nanoparticles and, subsequently, Ni–Fe alloy particles is observed. The latter have also been observed under static hydrogen reduction. Under strict control of the experimental parameters, the presented data therefore open an attractive chemically driven pathway to metal nanoarchitectures beyond the formation of “simple” nanoparticles.

Rhodium-Catalyzed Methanation and Methane Steam Reforming Reactions on Rhodium–Perovskite Systems: Metal–Support Interaction

Metal–support interaction in rhodium–perovskite systems was studied using LSF (La0.6Sr0.4FeO3−δ) and STF (SrTi0.7Fe0.3O3−δ) supports to disentangle different manifestations of strong or reactive metal–support interaction. Electron microscopy and catalytic characterization in methane steam reforming/CO2 methanation reveal that reduction in hydrogen at 673 K and 873 K causes different extents of Fe exsolution. Depending on the perovskite reducibility, Fe–Rh alloy particles are observed. No signs of strong metal–support interaction (i.e., encapsulation of metal particles) by reduced oxide species were observed. As re‐oxidation in oxygen at 873 K did not fully restore the initial structures, the interaction between Rh and the perovskites manifests itself in irreversible alloy formation. Catalytic effects are the suppression of methane reactivity with increasing prereduction temperature. The results show the limits of the strong metal–support interaction concept in complex metal–oxide systems.

Water-Gas Shift and Methane Reactivity on Reducible Perovskite-Type Oxides

Comparative (electro)catalytic, structural, and spectroscopic studies in hydrogen electro-oxidation, the (inverse) water-gas shift reaction, and methane conversion on two representative mixed ionic–electronic conducting perovskite-type materials La0.6Sr0.4FeO3−δ (LSF) and SrTi0.7Fe0.3O3−δ (STF) were performed with the aim of eventually correlating (electro)catalytic activity and associated structural changes and to highlight intrinsic reactivity characteristics as a function of the reduction state. Starting from a strongly prereduced (vacancy-rich) initial state, only (inverse) water-gas shift activity has been observed on both materials beyond ca. 450 °C but no catalytic methane reforming or methane decomposition reactivity up to 600 °C. In contrast, when starting from the fully oxidized state, total methane oxidation to CO2 was observed on both materials. The catalytic performance of both perovskite-type oxides is thus strongly dependent on the degree/depth of reduction, on the associated reactivity of the remaining lattice oxygen, and on the reduction-induced oxygen vacancies. The latter are clearly more reactive toward water on LSF, and this higher reactivity is linked to the superior electrocatalytic performance of LSF in hydrogen oxidation. Combined electron microscopy, X-ray diffraction, and Raman measurements in turn also revealed altered surface and bulk structures and reactivities.

Comprehensive evaluation of imidazole-based polymers for the enrichment of selected non-steroidal anti-inflammatory drugs

This study reports the comparison of four manufactured imidazole-based copolymers and two commercially available hydrophilic sorbents for the solid phase extraction (SPE) of selected non-steroidal anti-inflammatory drugs (NSAID). Different hydrophilic copolymers were obtained by a suspension polymerization using a styrene-based and a methacrylate-based cross-linker and by single step modifications for enhancing the ion-exchange character. SPE protocols were optimized for both non-modified and modified sorbents and applied for the enrichment of selected NSAID using all six copolymers. Comparison and evaluation were carried out by determining recovery rates of standard mixtures at different concentration levels ranging from 0.5mgL(-1) to 10mgL(-1) and by the enrichment of spiked human urine at two concentration levels. In order to gain insight into the complexity of the biological sample and its reduction after solid phase extraction, UHPLC-MS analysis and following database comparison was performed for the three mixed-mode strong anion-exchange sorbents. In order to prove the applicability of the modified imidazole-based polymers for the enrichment of NSAID in surface water, river water or groundwater, solid phase extraction was performed with 10ppb of NSAID which resulted into enhanced enrichment by a hundredfold.

Physico-chemical properties of unusual Ga2O3 polymorphs

A comparative structural and spectroscopic study, combined with reactivity tests in (inverse) water–gas shift and methanol steam reforming reaction, has been performed on various Ga2O3 polymorphs with special focus on δ-Ga2O3 and ε-Ga2O3 with the aim of highlighting the eventual intrinsic physico-chemical properties of the latter two. Using this comparative approach, the question whether δ-Ga2O3 in fact is a nanocrystalline modification of ε-Ga2O3, a mixture of ε-Ga2O3 and β-Ga2O3, or a single polymorphic form could be answered: especially Raman spectroscopy measurements, alongside reactivity tests, indicate that δ-Ga2O3 exhibits lots of properties of ε-Ga2O3. In fact, particularly in Raman measurements it appears as a mixture of ε-Ga2O3 and β-Ga2O3.Graphical abstract

Separation of Small Molecules on Novel Monolithic Poly(Vinylphosphonic Acid/Ethylene Dimethacrylate) Columns

In HPLC, monolithic organic stationary phases are usually restricted to the separation of high-molecular-weight compounds such as proteins or oligonucleotides. The aim of this study was to enlarge the applicability of monolithic stationary phases to the micro-liquid chromatography separation of smaller molecules. For this, a new monolithic stationary phase was synthesized by radical polymerization of vinylphosphonic acid (VPA) and ethylene dimethacrylate (EDMA) using azobisisobutyronitrile as radical initiator. In situ reactions at two different temperatures and reaction times resulted in poly(VPA/EDMA) capillaries and allowed fast separations for small molecules, especially parabens and alkylbenzenes. The capillaries showed high mechanical stability, low-swelling properties, high permeability and lower surface area as expected. Polymerization at 75°C for 20 min exhibited efficient separation of parabens within 1.5 min with short half-peak widths and satisfactory resolutions. Apart from attenuated total reflectance Fourier transform infrared (ATR-IR) measurements, the pH-dependent separation of alkylbenzenes confirmed the incorporation of phosphonate groups into the polymeric network, resulting into deprotonation of the stationary phase at pH >4. Moreover, methylparaben and propylparaben were quantitatively determined in human saliva after treatment with paraben-containing tooth paste.