Amélie Juhin

Angular dependence of core hole screening in LiCoO2: A DFT + U calculation of the oxygen and cobalt K-edge x-ray absorption spectra

Angular-dependent core hole screening effects have been found in the cobalt K-edge x-ray absorption spectrum of LiCoO2, using high-resolution data and parameter-free general gradient approximation plus U calculations. The Co 1s core hole on the absorber causes strong local attraction. The core hole screening on the cobalt nearest-neighbors induces a 2 eV shift in the density of states with respect to the on-site 1s-3d transitions, as detected in the Co K pre-edge spectrum. Our density functional theory plus U calculations reveal that the off-site screening is different in the out-of-plane direction, where a 3 eV shift is visible in both calculations and experiment. The detailed analysis of the inclusion of the core hole potential and the Hubbard parameter U shows that the core hole is essential for the off-site screening while U improves the description of the angular-dependent screening effects. In the case of oxygen K edge, both the core hole potential and the Hubbard parameter improve the relative positions of the spectral features.

X-ray Imaging of Zeolite Particles at the Nanoscale : Influence of Steaming on the State of Aluminum and the Methanol-To-Olefin Reaction

In view of the limited oil reserves the methanol-to-olefin (MTO) process is an interesting catalytic route to provide raw materials for chemical industries. In the last decades, a vast number of studies have been devoted to increase our understanding of this important catalytic reaction leading to a consensus concerning the mechanism.[1–4] Accordingly, MTO is thought to proceed through the so-called “hydrocarbon pool” (HCP) mechanism,[5, 6] in which methanol is added to an organic scaffold present within the zeolite framework. This is followed by elimination of olefinic species in a closed catalytic cycle. Microporous silicoaluminophosphates and aluminosilicates, such as SAPO-34 and ZSM-5, are often used as MTO catalysts because of their unique acidic and structural properties. In the case of ZSM-5 the formation of ethene and propene is governed by two different catalytic routes,[7,8] allowing in principle to control the ethene/propene ratio. Unfortunately, throughout the MTO reaction undesired carbon deposits are formed in the narrow micropore system of ZSM-5, leading to severely restricted diffusion and therefore limited catalytic activity.[9] To overcome these limitations efforts have been made to improve the pore accessibility during synthesis,[10–12] and/or in post-synthetic steps,[13, 14] resulting in significant improvements in the diffusion properties of ZSM-5. In this work, two commercial ZSM-5 zeolites with dimensions of approximately 200–800 nm have been studied by scanning transmission X-ray microscopy (STXM). The first sample, denoted as ZSM-5-C, was calcined for 6 h at 5508C, whereas the second sample, further labeled as ZSM-5-S, was steamed for 3 h at 7008C. Details on the preparation and characteristics of ZSM-5-C and ZSM-5-S can be found in the Supporting Information (Figures S1–S13, Tables S1–S6). We will show how STXM, in combination with bulk characterization techniques, allows investigating the physicochemical properties of ZSM-5 zeolites in a novel way at the nanoscale.[ 15, 16] More specifically, detailed chemical maps, with a spatial resolution of 70 nm, have been obtained of aluminum, oxygen, and carbon, even under realistic reaction conditions.[17–19] In this manner, the influence of steaming on the state of aluminum, that is, the coordination and spatial distribution, as well as on the MTO performance, has been unraveled.

X-ray Linear Dichroism in cubic compounds: the case of Cr3+ in MgAl2O4

The angular dependence (x-ray linear dichroism) of the

Detailed Characterization of a Nanosecond-Lived Excited State: X-ray and Theoretical Investigation of the Quintet State in Photoexcited [Fe(terpy)(2)](2+)

\text{Cr}\text{ }K

Direct evidence for an interdiffused intermediate layer in bi-magnetic core–shell nanoparticles

pre-edge in

Effect of atomic vibrations on the x-ray absorption spectra at the K edge of Al in α-Al2O3 and of Ti in TiO2 rutile

{\text{MgAl}}_{2}{\text{O}}_{4}:{\text{Cr}}^{3+}

Electronic structure and local environment of substitutional V3+ in grossular garnet Ca3Al2(SiO4)3: K-edge X-ray absorption spectroscopy and first-principles modeling

spinel is measured by means of x-ray absorption near-edge structure spectroscopy and compared to calculations based on density functional theory (DFT) and ligand field multiplet (LFM) theory. We also present an efficient method, based on symmetry considerations, to compute the dichroism of the cubic crystal starting from the dichroism of a single substitutional site. DFT shows that the electric dipole transitions do not contribute to the features visible in the pre-edge and provides a clear vision of the assignment of the

Understanding the Photomagnetic Behavior in Copper Octacyanomolybdates

1s\ensuremath{\rightarrow}3d

Structure refinement of a synthetic knorringite, Mg3(Cr0.8Mg0.1Si0.1)2(SiO4)3

transitions. However, DFT is unable to reproduce quantitatively the angular dependence of the pre-edge, which is, on the other side, well reproduced by LFM calculations. The most relevant factors determining the dichroism of

Site symmetry and crystal symmetry: a spherical tensor analysis

\text{Cr}\text{ }K