1s2p resonant inelastic X-ray scattering combined dipole and quadrupole analysis method.

In this study an analysis strategy towards using the resonant inelastic X-ray scattering (RIXS) technique more effectively compared with X-ray absorption spectroscopy (XAS) is presented. In particular, the question of when RIXS brings extra information compared with XAS is addressed. To answer this question the RIXS plane is analysed using two models: (i) an exciton model and (ii) a continuum model. The continuum model describes the dipole pre-edge excitations while the exciton model describes the quadrupole excitations. Applying our approach to the experimental 1s2p RIXS planes of VO2 and TiO2, it is shown that only in the case of quadrupole excitations being present is additional information gained by RIXS compared with XAS. Combining this knowledge with methods to calculate the dipole contribution in XAS measurements gives scientists the opportunity to plan more effective experiments.

New method for analysis of nanoparticle geometry in supported fcc metal catalysts with scanning transmission electron microscopy.

To apply the knowledge of reaction mechanisms of heterogeneously catalyzed reactions on the atomic scale to supported catalyst systems, a detailed description of the structure of active particles on the atomic scale is required. In this article, a method is developed to construct atomic-scale geometric models for supported active fcc metal nanoparticles, based on a measurement of particle sizes and particle volumes by Scanning Transmission Electron Microscopy (STEM) and the M-M coordination number determined from EXAFS. The method is applied to supported Au/TiO(2), Au/MgAl(2)O(4)(-), and Au/Al(2)O(3) catalysts. These geometric models allow for estimation of geometric properties, such as specific Au surface area, metal-support contact perimeter, metal-support contact surface area, edge length, and number of Au atoms located at the corners of the particles, with an error on the order of 20%. In the three catalysts studied here we find that the Au particles in the Al(2)O(3) supported catalyst are small. The Au particles in the Au/TiO(2) catalyst are smaller in diameter than those for the Au/MgAl(2)O(4), but also thicker. The differences in particle size and shape seem to reflect the differences in the metal-support interface energy in the three catalyst systems.