Nanoscale determination of interatomic distance by ptychography-EXAFS method using advanced Kirkpatrick-Baez mirror focusing optics

This work demonstrates a combination technique of X-ray ptychography and the extended X-ray absorption fine structure (ptychography-EXAFS) method, which can determine the interatomic distances of bulk materials at the nanoscale. In the high-resolution ptychography-EXAFS method, it is necessary to use high-intense coherent X-rays with a uniform wavefront in a wide energy range, hence a ptychographic measurement system installed with advanced Kirkpatrick-Baez mirror focusing optics is developed and its performance is evaluated. Ptychographic diffraction patterns of micrometre-size MnO particles are collected by using this system at 139 energies between 6.504 keV and 7.114 keV including the Mn K absorption edge, and then the EXAFS of MnO is derived from the reconstructed images. By analyzing the EXAFS spectra obtained from a 48 nm × 48 nm region, the nanoscale bond lengths of the first and second coordination shells of MnO are determined. The present approach has great potential to elucidate the unclarified relationship among the morphology, electronic state and atomic arrangement of inhomogeneous bulk materials with high spatial resolution.

Visualization of Heterogeneous Oxygen Storage Behavior in Platinum-Supported Cerium-Zirconium Oxide Three-Way Catalyst Particles by Hard X-ray Spectro-Ptychography

The cerium density and valence in micrometer-size platinum-supported cerium-zirconium oxide Pt/Ce₂ Zr₂ O_x (x=7-8) three-way catalyst particles were successfully mapped by hard X-ray spectro-ptychography (ptychographic-X-ray absorption fine structure, XAFS). The analysis of correlation between the Ce density and valence in ptychographic-XAFS images suggested the existence of several oxidation behaviors in the oxygen storage process in the Ce₂ Zr₂ O_x particles. Ptychographic-XAFS will open up the nanoscale chemical imaging and structural analysis of heterogeneous catalysts.

Imaging of Oxygen Diffusion in Individual Platinum/Ce2 Zr2 Ox Catalyst Particles During Oxygen Storage and Release

The spatial distribution of Ce(3+) and Ce(4+) in each particle of Ce2 Zr2 Ox in a three-way conversion catalyst system was successfully imaged during an oxygen storage/release cycle by scanning X-ray absorption fine structure (XAFS) using hard X-ray nanobeams. For the first time, nano-XAFS imaging visualized and identified the modes of non-uniform oxygen diffusion from the interface of Pt catalyst and Ce2 Zr2 Ox support and the active parts in individual catalyst particles.

Degradation mechanism of a high-performance real micro gas sensor, as determined by spatially resolved XAFS

Of late, battery-driven high-performance gas sensors have gained acceptability in practical usage, whose atomic-scale structure has been revealed by μ-fluorescence X-ray absorption fine structure analysis. We studied the chemical distribution of Pd species in the Pd/Al2O3 catalyst overlayer in the real gas sensor at various degrees of deterioration. In a freshly prepared sensor, all Pd species were in the PdO form; in a heavily deteriorated sensor, Pd/Al2O3 in the external region changed to metallic Pd particles, while the PdO structure in the inner region near the heater remained unchanged. The Pd species distribution was in agreement with the simulated thermal distribution. Temperature control was crucial to maintain the high performance of the gas sensor. The improved sensor allows homogeneous heating and has a lifetime of more than 5 years.

Nanoparticles-in-concavities as efficient nanocatalysts for carbon dioxide reforming of methane to hydrogen and syngas

The ceria concavity-loaded Ni nanoparticle catalysts can lead to more active sites and promote CO₂ dissociative activation and CO desorption, thus enhancing significantly the catalytic performances for methane dry reforming with CO₂.

Active Site Elucidation in Heterogeneous Catalysis via In Situ X-Ray Spectroscopies

Nanostructured heterogeneous catalysts will play a key role in the development of robust artificial photosynthetic systems for water photooxidation and CO2 photoreduction. Identifying the active site responsible for driving these chemical transformations remains a significant barrier to the design of tailored catalysts, optimized for high activity, selectivity, and lifetime. This highlight reveals how select recent breakthroughs in the application of in situ surface and bulk X-ray spectroscopies are helping to identify the active catalytic sites in a range of liquid and gas phase chemistry.