Atomic-Scale Investigation of Two-Component MoVO Complex Oxide Catalysts Using Aberration-Corrected High-Angle Annular Dark-Field Imaging

Abstract

High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) imaging was used to study various hydrothermally prepared MoVO phases with either M1-type orthorhombic symmetry, Mo5O14-type tetragonal symmetry, or trigonal symmetry. For the M1-type phase, HAADF analysis suggests atomic positions consistent with existing M1 models having mixed Mo and V occupancy in the octahedral sites linking the pentagonal units. For the V-substituted Mo5O14 phase, contrast analysis provides evidence of V occupation primarily in the linking octahedra that interconnect the pentagonal {Mo6O21} units. Selected-area electron diffraction (SAED) studies suggest that the structure of the Mo5O14 analog is likely to be tetragonal, rather than orthorhombically distorted as has previously been proposed. HAADF analysis of the trigonal phase provides reasonable support for previously reported structural models. High-resolution images provide strong support for the existence of atomic disorder within the octahedral sites connecting the three heptagonal channels that characterize this structure.

Direct Imaging of Octahedral Distortion in a Complex Molybdenum Vanadium Mixed Oxide

“…It provided valuable insights on different metal site occupancies and defect structures. [2,12] In the case of highly crystalline (Mo,V)O x ( Figure SI 1), the analysis of HAADF images ( Figure 2A) showed a similar trend in the Mo site occupancy ( Figure SI 2). Using the labelling scheme suggested by DeSanto [8] et al, the Mo content in the respective sites decreases in the order S9 ≈ S5≈ S6 > S8 ≈ S10≈ S11 > S2 > S4 ≈ S3 ≈ S7 > S1.…”

Improvement of the Structural Model for the M1 Phase Mo–V–Nb–Te–O Propane (Amm)oxidation Catalyst

“…A second objective of the present study is to recognize that the Mo 5 O 14 -type impurity phase is actually a V-substituted variant of this structure type by including this in the Rietveld analysis [26]. A third objective of this study is to account for a previously unidentified impurity; a Mosubstituted V 2 O 5 -type structure in the Rietveld refinement.…”

Aberration-corrected scanning transmission electron microscopy for atomic-resolution studies of functional oxides

“…It may be noted that Pyrz and coworkers also used column intensities to infer column contents in their work. 76,78 Moving beyond bulk materials, thin films are a particularly rich field of application for all techniques based on transmission electron microscopy, because while X-ray diffraction yields valuable information, giving a nanostructural context to explain the diffraction information is essential. This was clearly the case in the seminal paper of Zeches et al 17 on the growth of thin films of bismuth ferrite on YAlO 3 and LaAlO 3 .…”