In Situ Multimodal 3D Chemical Imaging of a Hierarchically Structured Core@Shell Catalyst

Abstract

A Cu/ZnO/AlO@ZSM-5 core@shell catalyst active for one-step conversion of synthesis gas to dimethyl ether (DME) was imaged simultaneously and in situ using synchrotron-based micro X-ray fluorescence (μ-XRF), X-ray diffraction (μ-XRD), and scanning transmission X-ray microscopy (STXM) computed tomography (CT) with micrometer spatial resolution. An identical sample volume was imaged stepwise, first under oxidizing and reducing atmospheres (imitating calcination and activation processes), and then under model reaction conditions for DME synthesis (H:CO:CO ratio of 16:8:1, up to 250 °C). The multimodal imaging methods offered insights into the active metal structure and speciation within the catalyst, and allowed imaging of both the catalyst core and zeolite shell in a single acquisition. Dispersion of nanosized Cu species was observed in the catalyst core during reduction, with formation of a metastable Cu phase at the core-shell interface. Under DME reaction conditions at 1 bar, the coexistence of Cu in the active catalyst core together with partially oxidized Cu species was unraveled. The zeolite shell and core-shell interface remained stable under all conditions, preserving the bifunctional nature of the catalyst. These observations are inaccessible using standard bulk techniques like X-ray absorption spectroscopy (XAS) and XRD, demonstrating the potential of multimodal in situ X-ray CT for characterization of hierarchically designed materials, which stand to benefit tremendously from such 3D spatially resolved measurements.

Operando XAFS Imaging of Distribution of Pt Cathode Catalysts in PEFC MEA

“…J. Grunwaldt, et al. simultaneously visualized a multi‐elemental core‐shell catalyst particle by multimoidal imaging techniques of μ‐XRF, μ‐XRD, and STXM‐CT and revealed the presence and properties of a metastable structure during reactions . We have succeeded in hard X‐ray spectro‐ptychography at Ce L III ‐edge of Ce 2 Zr 2 O x solid‐solution particles for three‐way exhaust catalysts and several reaction modes were found in the oxygen storage process of the Ce 2 Zr 2 O x particles …”

Moving Frontiers in Transition Metal Catalysis: Synthesis, Characterization and Modeling

“…In this case, the colloidal, Cu/Zn‐based NPs were used as precursor for the methanol active component and immobilized directly on the solid acid dehydration catalyst. Alternatively, also core@shell Cu/ZnO/Al 2 O 3 @ZSM‐5 catalysts have been used . Again X‐ray techniques are excellent tools, namely to uncover the hierarchical structure.…”

“…Again X‐ray techniques are excellent tools, namely to uncover the hierarchical structure. [51c,64] Using synchrotron‐based micro X‐ray fluorescence, micro XRD, and scanning transmission X‐ray microscopy computed tomography (CT), the evolution of Cu/ZnO and zeolite components were analyzed in a single catalyst grain during calcination, reduction, and under DME synthesis conditions . The X‐ray CT allowed to identify a metastable Cu + phase at the core–shell interface.…”

Structural Evolution of Highly Active Multicomponent Catalysts for Selective Propylene Oxidation

“…Furthermore, while the X-ray imaging toolset has great variety, the compromise between field of view, spatial resolution, and measurement time should be carefully considered [29][30][31]. Likewise, progressing from quasi in situ to full in situ or operando imaging is of great interest in catalysis but is experimentally challenging [32,33,52,53]. However, the quasi in situ approach is technically simple, potentially attractive, and may be expanded to monitor structural behaviour of other catalyst systems.…”

“…The high penetration of X-rays allows measurement of large samples, such as entire catalyst grains, combined with large fields of view and spatial resolution on the nm to µm scale. Furthermore, by applying computed tomography (CT) and three-dimensional (3D) image reconstruction, it is possible to retrieve chemical and structural data from the interior of catalyst bodies in a noninvasive manner [32][33][34]. Extending spatial resolution to 3D is a powerful advantage for the study of heterogeneous catalysts, which often contain delicate or fine structural features that are intimately linked to the catalyst function, as notably demonstrated for fluid catalytic cracking catalysts [35][36][37][38][39].…”