Synergy between XANES Spectroscopy and DFT to Elucidate the Amorphous Structure of Heterogeneous Catalysts: TiO₂‐Supported Molybdenum Oxide Catalysts

Abstract

Active phase of a catalyst: Using the 3D structural characterization of the environment around Mo atoms provided by X‐ray absorption near‐edge structure spectroscopy (left; spectrum of the MoK edge) and DFT calculations, the molecular‐scale structure of a TiO2‐supported molybdenum oxide catalyst was defined. The structure consists of Mo octahedra arranged in a six‐membered ring.

Surface-dependent sulfidation and orientation of MoS2 slabs on alumina-supported model hydrodesulfurization catalysts

“…XPS was used to quantify the sulfidation degree through the methodology developed by Gandubert et al [12] (Figure 1). with enhanced intensity for four-fold coordination [25]. whose positions and relative intensities are in good agreement with AHM features.…”

“…whose positions and relative intensities are in good agreement with AHM features. Thus, it can be concluded that the speciation of molybdenum in the oxide state is relatively similar on A , C (0001), M and R planes which can be explained by the presence of polymolybdate-like species with Mo located in edge-shared octahedral [25,26]. More specific information on a potential surface-dependent orientation of supported polymolybdate species can be obtained by comparing the spectra when the electric field vector of the synchrotron beam is set parallel or perpendicular to the surface of the single crystal wafer.…”

“…More specific information on a potential surface-dependent orientation of supported polymolybdate species can be obtained by comparing the spectra when the electric field vector of the synchrotron beam is set parallel or perpendicular to the surface of the single crystal wafer. In the case of an oriented adsorption of polymolybdate on the surface, the XANES region should exhibit dissimilarities between both polarizations [27][28][29] since Mo atoms are non equivalent in polyoxomolybdate species and each of them contributes directly to the relative intensity of the different maxima [25].…”

X-ray absorption near edge spectroscopy of thermochromic phase transition in CuMoO4

“…2(c)). The amplitude of the preedge shoulder depends on the degree of the MoO6 octahedra distortion and 4d(Mo)/2p(O) orbital mixing and is the largest for tetrahedral MoO4 coordination [39]. Therefore, it can be used to monitor the γ-to-α phase transition in CuMoO4.…”

A First‐Cycle Coulombic Efficiency Higher than 100 % Observed for a Li2MO3 (M=Mo or Ru) Electrode

“…[12] In contrast, the pre-edge peak is stronger in MoO 3 because the local symmetry of the MoO 6 octahedron is low due to four shorter Mo-O bonds and two longer Mo-O bonds. [13] The pristine Li 2 MoO 3 electrode does not show a pre-edge like that in MoO 2 because the Mo 4+ ions in Li 2 MoO 3 are located in the ordinary octahedral sites. [14] After the first-cycle de-lithiation, however, a pre-edge like that in MoO 3 develops in the Li 2 MoO 3 electrode, implying that the Mo valence is Mo 6+ in the de-lithiated Li 2 MoO 3 electrode.…”