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Volume 90 Issue 50 | p. 44 | Concentrates
Issue Date: December 10, 2012

X-raying Catalysts In Action

Tomography method monitors changes in chemically distinct nanoscale regions of catalysts under reaction conditions
Department: Science & Technology
News Channels: Analytical SCENE, Nano SCENE
Keywords: catalysis, in-stu, operando, X-ray absorption
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An X-ray tomography method maps the distribution of Fe (red), Zn (green), and Ti and K (orange, yellow, and white) species in a single catalyst particle.
Credit: Angew. Chem. Int. Ed.
An X-ray tomography method maps the distribution of Fe (red), Zn (green), and Ti and K species (orange, yellow, and white in order of increasing concentration) in a single micrometer-sized Fisher-Tropsch catalyst particle.
 
An X-ray tomography method maps the distribution of Fe (red), Zn (green), and Ti and K (orange, yellow, and white) species in a single catalyst particle.
Credit: Angew. Chem. Int. Ed.

Thanks to a specially designed reactor cell, researchers can now probe changes in the chemical composition, morphology, porosity, and other properties of individual 20-μm-sized catalyst particles as the particles mediate chemical reactions (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201204930). The study conducted by Joy C. Andrews of SLAC National Accelerator Laboratory; Bert M. Weckhuysen of Utrecht University, in the Netherlands; and coworkers demonstrates a procedure for exploiting high-energy X-ray microscopy to penetrate deeply into complex materials and resolve chemically distinct nanoscale regions within their bulk. Solid catalysts often undergo substantial changes—sometimes beneficial, sometimes detrimental—upon exposure to reactive chemicals at high temperature and pressure. Mapping those changes in three dimensions as they occur could lead to improved catalysts, but capturing the information remains challenging. To demonstrate the new method’s capabilities, the team probed a model Fischer-Tropsch C–C coupling catalyst as it was exposed to 10 atm of a mixture of H2 and CO at 350 °C. The method pinpointed regions rich in Fe2O3, Fe2TiO5, Fe3O4, ZnO, and K2O and monitored the evolution of those regions over the course of several hours.

Over the course of several hours’ exposure to H2 and CO at high temperature and high pressure, the chemical composition of this 20-µm-diameter catalyst particle evolves. Fe2TiO5 is green, Fe2O3 is red, and Fe3O4 is blue.
Credit: Angew. Chem. Int. Ed.
This rotating X-ray tomography reconstruction reveals the three-dimensional distribution of Fe (red), Zn (green), and Ti and K (orange, yellow, and white) species in a single 20-µm-diameter catalyst particle.
Credit: Angew. Chem. Int. Ed.
 
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