Nanoscale chemical imaging of a working catalyst by scanning transmission X-ray microscopy

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Abstract

The modern chemical industry uses heterogeneous catalysts in almost every production process1. They commonly consist of nanometre-size active components (typically metals or metal oxides) dispersed on a high-surface-area solid support, with performance depending on the catalysts’ nanometre-size features and on interactions involving the active components, the support and the reactant and product molecules. To gain insight into the mechanisms of heterogeneous catalysts, which could guide the design of improved or novel catalysts, it is thus necessary to have a detailed characterization of the physicochemical composition of heterogeneous catalysts in their working state at the nanometre scale1,2. Scanning probe microscopy methods have been used to study inorganic catalyst phases at subnanometre resolution3,4,5,6, but detailed chemical information of the materials in their working state is often difficult to obtain5,6,7. By contrast, optical microspectroscopic approaches offer much flexibility for in situ chemical characterization; however, this comes at the expense of limited spatial resolution8,9,10,11. A recent development promising high spatial resolution and chemical characterization capabilities is scanning transmission X-ray microscopy4,12,13, which has been used in a proof-of-principle study to characterize a solid catalyst14. Here we show that when adapting a nanoreactor specially designed for high-resolution electron microscopy7, scanning transmission X-ray microscopy can be used at atmospheric pressure and up to 350 °C to monitor in situ phase changes in a complex iron-based Fisher–Tropsch catalyst and the nature and location of carbon species produced. We expect that our system, which is capable of operating up to 500 °C, will open new opportunities for nanometre-resolution imaging of a range of important chemical processes taking place on solids in gaseous or liquid environments.

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Figure 1: Experimental set-up and data acquisition method.
Figure 2: Chemical contour maps and X-ray absorption spectra of the catalyst material during the different stages of reaction.
Figure 3: Location and nature of carbon species on the catalyst material.

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Acknowledgements

We acknowledge financial support for this research work from the Dutch National Science Foundation in the form of two VICI grants (to F.M.F.d.G. and B.M.W.), a grant from the Netherlands Research School Combination on Catalysis (to B.M.W. and F.M.F.d.G.) and a grant from Shell Global Solutions (to B.M.W.). The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, US Department of Energy. The nanoreactors were fabricated with the assistance of the DIMES ICP-group and the Nanofacility of TU Delft.

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Correspondence to Bert M. Weckhuysen or Frank M. F. de Groot.

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de Smit, E., Swart, I., Creemer, J. et al. Nanoscale chemical imaging of a working catalyst by scanning transmission X-ray microscopy. Nature 456, 222–225 (2008) doi:10.1038/nature07516

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