Better Catalysts through Microscopy: Mesoscale M1/M2 Intergrowth in Molybdenum–Vanadium Based Complex Oxide Catalysts for Propane Ammoxidation

Abstract

In recent decades, catalysis research has transformed from the predominantly empirical field to one where it is possible to control the catalytic properties via characterization and modification of the atomic-scale active centers. Many phenomena in catalysis, such as synergistic effect, however, transcend the atomic scale and also require the knowledge and control of the mesoscale structure of the specimen to harness. In this paper, we use our discovery of atomic-scale epitaxial interfaces in molybdenum-vanadium based complex oxide catalysts systems (i.e., Mo-V-M-O, M = Ta, Te, Sb, Nb, etc.) to achieve control of the mesoscale structure of this complex mixture of very different active phases. We can now achieve true epitaxial intergrowth between the catalytically critical M1 and M2 phases in the system that are hypothesized to have synergistic interactions, and demonstrate that the resulting catalyst has improved selectivity in the initial studies. Finally, we highlight the crucial role atomic scale characterization and mesoscale structure control play in uncovering the complex underpinnings of the synergistic effect in catalysis.

Characterization of MoVTeNbOx Catalysts during Oxidation Reactions Using In Situ/Operando Techniques: A Review

“…One additional factor to be considered is that the time of experiments by some researchers may not be long enough to observe significant changes. Even the presence of the M2 phase affecting selectivity in propane ammoxidation is not agreed upon [15,50,52]. The roles of active exposed planes during the reaction are also debated [77,80].…”

“…However, the presence of M2 phase in the catalytic system is found to improve acrylonitrile selectivity [15,50], although a recent study by Woo et al suggested the M1 phase is the only phase required for both the activity and selectivity in propane ammoxidation [52]. The STEM microscopy approach has been adopted to analyze the synergetic effects of this M1/M2 mixture [15,51].…”

A machine perspective of atomic defects in scanning transmission electron microscopy

“…Therefore, NMF provides a natural representation of components that is consistent with physical constraints, which makes it an excellent phase mapping method. As an example, in the case of a Mo‐V‐Te‐Ta oxide catalyst, M1 and M2 phases coexist with a clear boundary visible in the STEM image. A stack of FFT spectra is collected by sliding a window of a fixed size across the STEM image of the oxide catalyst (Figure F).…”

Electron‐Irradiation‐Stimulated Atomic‐Scale Structural Dynamics of the Pentagonal Channel in a Complex MoVTeNbOx Catalyst

“…Very recently, He et al. revealed epitaxial M1/M2 intergrowth, which are both catalytically active . However, knowledge of how the complex oxide behaves under unavoidable electron‐beam irradiation during electron microscopy characterization is still lacking.…”

“…The phase‐pure M1 catalyst was synthesized by using a hydrothermal method . The chemical composition of the M1 phase is listed as (65.6±0.5) at % molybdenum, (16.5±0.6) at % vanadium, (6.7±0.3) at % tellurium, and (11.3±0.4) at % niobium .…”