8 research outputs found
Grazing angle X-ray fluorescence from periodic structures on silicon and silica surfaces
Various 3-dimensional nano-scaled periodic structures with different configurations and periods deposited on the surface of silicon and silica substrates were investigated by means of the grazing incidence and grazing emission X-ray fluorescence techniques. Apart from the characteristics which are typical for particle- and layer-like samples, the measured angular intensity profiles show additional periodicity-related features. The latter could be explained by a novel theoretical approach based on simple geometrical optics (GO) considerations. The new GO-based calculations were found to yield results in good agreement with experiment, also in cases where other theoretical approaches are not valid, e.g., periodic particle distributions with an increased surface coverage
Revealing the bonding of solvated Ru complexes with valence-to-core resonant inelastic X-ray scattering
Ru-complexes are widely studied because of their use in biological applications and photoconversion technologies. We reveal novel insights into the chemical bonding of a series of Ru(ii)- and Ru(iii)-complexes by leveraging recent advances in high-energy-resolution tender X-ray spectroscopy and theoretical calculations. We perform Ru 2p4d resonant inelastic X-ray scattering (RIXS) to probe the valence excitations in dilute solvated Ru-complexes. Combining these experiments with a newly developed theoretical approach based on time-dependent density functional theory, we assign the spectral features and quantify the metal-ligand bonding interactions. The valence-to-core RIXS features uniquely identify the metal-centered and charge transfer states and allow extracting the ligand-field splitting for all the complexes. The combined experimental and theoretical approach described here is shown to reliably characterize the ground and excited valence states of Ru complexes, and serve as a basis for future investigations of ruthenium, or other 4d metals active sites, in biological and chemical applications
Millimeter scale variations in the isotopic composition of vein sulphide minerals in the Kupferschiefer deposits, Lubin area, SW Poland
Systematic Structure–Property Relationship Studies in Palladium-Catalyzed Methane Complete Combustion
To
limit further rising levels in methane emissions from stationary
and mobile sources and to enable promising technologies based on methane,
the development of efficient combustion catalysts that completely
oxidize CH<sub>4</sub> to CO<sub>2</sub> and H<sub>2</sub>O at low
temperatures in the presence of high steam concentrations is required.
Palladium is widely considered as one of the most promising materials
for this reaction, and a better understanding of the factors affecting
its activity and stability is crucial to design even more improved
catalysts that efficiently utilize this precious metal. Here we report
a study of the effect of three important variables (particle size,
support, and reaction conditions including water) on the activity
of supported Pd catalysts. We use uniform palladium nanocrystals as
catalyst precursors to prepare a library of well-defined catalysts
to systematically describe structure–property relationships
with help from theory and in situ X-ray absorption spectroscopy. With
this approach, we confirm that PdO is the most active phase and that
small differences in reaction rates as a function of size are likely
due to variations in the surface crystal structure. We further demonstrate
that the support exerts a limited influence on the PdO activity, with
inert (SiO<sub>2</sub>), acidic (Al<sub>2</sub>O<sub>3</sub>), and
redox-active (Ce<sub>0.8</sub>Zr<sub>0.2</sub>O<sub>2</sub>) supports
providing similar rates, while basic (MgO) supports show remarkably
lower activity. Finally, we show that the introduction of steam leads
to a considerable decrease in rates that is due to coverage effects,
rather than structural and/or phase changes. Altogether, the data
suggest that to further increase the activity and stability of Pd-based
catalysts for methane combustion, increasing the surface area of supported
PdO phases while avoiding strong adsorption of water on the catalytic
surfaces is required. This study clarifies contrasting reports in
the literature about the active phase and stability of Pd-based materials
for methane combustion