Structural evolution after oxidative pretreatment and CO oxidation of Au nanoclusters with different ligand shell composition: a view on the Au core

The reactivity of supported monolayer protected Au nanoclusters is directly affected by their structural dynamics under pretreatment and reaction conditions. The effect of different types of ligands of Au clusters supported on CeO$_2$ on their core structure evolution, under oxidative pretreatment and CO oxidation reaction, was investigated. X-ray absorption and X-ray photoelectron spectroscopy studies revealed that the clusters evolve to a similar core structure above 250 °C in all the cases, indicating the active role of the ligand–support interaction in the reaction

Ice Nucleation Activity of Graphene and Graphene Oxides

Aerosols can act as cloud condensation nuclei and/or ice-nucleating particles (INPs), influencing cloud properties. In particular, INPs show a variety of different and complex mechanisms when interacting with water during the freezing process. To gain a fundamental understanding of the heterogeneous freezing mechanisms, studies with proxies for atmospheric INPs must be performed. Graphene and its derivatives offer suitable model systems for soot particles, which are ubiquitous aerosols in the atmosphere. In this work, we present an investigation of the ice nucleation activity (INA) of different types of graphene and graphene oxides. Immersion droplet freezing experiments as well as additional analytical analyses, such as X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy, were performed. We show within a group of samples that a highly ordered graphene lattice (Raman G band intensity >50%) can support ice nucleation more effectively than a lowly ordered graphene lattice (Raman G band intensity <20%). Ammonia-functionalized graphene revealed the highest INA of all samples. Atmospheric ammonia is known to play a primary role in the formation of secondary particulate matter, forming ammonium-containing aerosols. The influence of functionalization on interactions between the particle interface and water molecules, as well as on hydrophobicity and agglomeration processes, is discussed

Molecular spectroscopy for ground-state transfer of ultracold RbCs molecules

We perform one- and two-photon high resolution spectroscopy on ultracold samples of RbCs Feshbach molecules with the aim to identify a suitable route for efficient ground-state transfer in the quantum-gas regime to produce quantum gases of dipolar RbCs ground-state molecules. One-photon loss spectroscopy allows us to probe deeply bound rovibrational levels of the mixed excited (A1{\Sigma}+ - b3{\Pi}0) 0+ molecular states. Two-photon dark state spectroscopy connects the initial Feshbach state to the rovibronic ground state. We determine the binding energy of the lowest rovibrational level |v"=0,J"=0> of the X1{\Sigma}+ ground state to be DX 0 = 3811.5755(16) 1/cm, a 300-fold improvement in accuracy with respect to previous data. We are now in the position to perform stimulated two-photon Raman transfer to the rovibronic ground state.Comment: Submitted to PCCP themed issue: Physics and Chemistry of Cold Molecule

The Chemical Evolution of the La0.6Sr0.4CoO3−δ Surface Under SOFC Operating Conditions and Its Implications for Electrochemical Oxygen Exchange Activity

© The Author(s) 2018Owing to its extraordinary high activity for catalysing the oxygen exchange reaction, strontium doped LaCoO3 (LSC) is one of the most promising materials for solid oxide fuel cell (SOFC) cathodes. However, under SOFC operating conditions this material suffers from performance degradation. This loss of electrochemical activity has been extensively studied in the past and an accumulation of strontium at the LSC surface has been shown to be responsible for most of the degradation effects. The present study sheds further light onto LSC surface changes also occurring under SOFC operating conditions. In-situ near ambient pressure X-ray photoelectron spectroscopy measurements were conducted at temperatures between 400 and 790 °C. Simultaneously, electrochemical impedance measurements were performed to characterise the catalytic activity of the LSC electrode surface for O2 reduction. This combination allowed a correlation of the loss in electro-catalytic activity with the appearance of an additional La-containing Sr-oxide species at the LSC surface. This additional Sr-oxide species preferentially covers electrochemically active Co sites at the surface, and thus very effectively decreases the oxygen exchange performance of LSC. Formation of precipitates, in contrast, was found to play a less important role for the electrochemical degradation of LSC.Fonds zur Förderung der wissenschaftlichen Forschung (FWF)212921411

Roadmap on exsolution for energy applications

Over the last decade, exsolution has emerged as a powerful new method for decorating oxide supports with uniformly dispersed nanoparticles for energy and catalytic applications. Due to their exceptional anchorage, resilience to various degradation mechanisms, as well as numerous ways in which they can be produced, transformed and applied, exsolved nanoparticles have set new standards for nanoparticles in terms of activity, durability and functionality. In conjunction with multifunctional supports such as perovskite oxides, exsolution becomes a powerful platform for the design of advanced energy materials. In the following sections, we review the current status of the exsolution approach, seeking to facilitate transfer of ideas between different fields of application. We also explore future directions of research, particularly noting the multi-scale development required to take the concept forward, from fundamentals through operando studies to pilot scale demonstrations

Polarization-Dependent SFG Spectroscopy of Near Ambient Pressure CO Adsorption on Pt(111) and Pd(111) Revisited

Polarization-dependent sum frequency generation (SFG) vibrational spectroscopy was employed to examine CO overlayers on Pt(111) and Pd(111) single crystal surfaces at room temperature. Utilizing different polarization combinations (SSP and PPP) of the visible and SFG light allows to determine the molecular orientation (tilt angle) of interface molecules but the analysis of the measured Ippp/Issp is involved and requires a proper optical interface model. For CO/Pt(111), the hyperpolarizability ratio (R=βaac/βccc=βbbc/βccc) is not exactly known and varying R in the range 0.1–0.5 yields tilt angles of 40°–0°, respectively. Based on the known perpendicular adsorption of CO on Pt, an exact R-value of 0.49 was determined. Polarization-dependent SFG spectra in the pressure range 10−4 to 36 mbar did not indicate any change of the tilt angle of adsorbed CO. Modeling also indicated a strong dependence of Ippp/Issp on the incidence angles of visible and IR laser beams. Complementing previous low temperature/low pressure data, room temperature CO adsorption on Pd(111) was examined from 10−6 to 250 mbar. The absolute PPP and SSP spectral intensities on Pt and Pd were simulated, as well as the expected Ippp/Issp ratios. Although CO on Pt and Pd should exhibit similar intensities (at high CO coverage), the higher Ippp/Issp ratio for Pd (48 vs. 27 on Pt) renders the detection of adsorbed CO in SSP spectra difficult. The presence or absence of CO species in SSP spectra can thus not simply be correlated to tilted or perpendicular CO molecules, respectively. Careful modeling, including not only molecular and interface properties, but also the experimental configuration (incidence angles), is certainly required even for seemingly simple adsorbate–substrate systems.Austrian Science Fund (FWF

In Situ Growth of Exsolved Nanoparticles under Varying rWGS Reaction Conditions&mdash;A Catalysis and Near Ambient Pressure-XPS Study

Perovskite-type oxides are highly flexible materials that show properties that are beneficial for application in reverse water-gas shift processes (rWGS). Due to their stable nature, the ability to incorporate catalytically active dopants in their lattice structure, and the corresponding feature of nanoparticle exsolution, they are promising candidates for a materials design approach. On an industrial level, the rWGS has proven to be an excellent choice for the efficient utilisation of CO2 as an abundant and renewable carbon source, reflected by the current research on novel and improved catalyst materials. In the current study, a correlation between rWGS reaction environments (CO2 to H2 ratios and temperature), surface morphology, and catalytic activity of three perovskite catalysts (Nd0.6Ca0.4Fe0.9Co0.1O3-&delta;, Nd0.6Ca0.4Fe0.97Co0.03O3-&delta;, and Nd0.6Ca0.4Fe0.97Ni0.03O3-&delta;) is investigated, combining catalytic measurements with SEM and NAP-XPS. The materials were found to react dynamically to the conditions showing both activation due to in situ nanoparticle exsolution and deactivation via CaCO3 formation. This phenomenon could be influenced by choice of material and conditions: less reductive conditions (larger CO2 to H2 or lower temperature) lead to smaller exsolved particles and reduced carbonate formation. However, the B-site doping was also important; only with 10% Co-doping, a predominant activation could be achieved