Web Date: July 24, 2008
Catalysts Under Pressure
A team of researchers has recorded atomic-resolution transmission electron microscopy (TEM) images of catalyst particles (shown) while the solids were exposed to relatively high pressures of reactive gas (1 atm H2) and heated to 500 °C (Ultramicroscopy, DOI: 10.1016/j.ultramic.2008.04.014). The imaging experiment, which was conducted at 100 times greater pressure than in previous TEM studies, may lead to new ways of probing materials that undergo subtle but important structural changes as chemical reactions proceed on their surfaces.
Generally, researchers aiming to record atomic-resolution TEM images conduct their experiments under high vacuum and at moderate temperatures because higher pressures and temperatures limit resolution and image quality. The usual imaging conditions, however, differ greatly from typical industrial catalytic reaction conditions, which may alter a catalyst's structure from an inactive to a catalytically active form. To get an up-close view of catalysts under demanding conditions, J. Fredrik Creemer of Delft University of Technology, in the Netherlands; Stig Helveg of catalyst manufacturer Haldor Topsøe, in Denmark; and coworkers designed a TEM-compatible microreactor and used it to probe a Cu/ZnO methanol-synthesis catalyst. While activating the catalyst at high temperature in hydrogen, the team directly observed the growth, structure, and evolution of copper nanocrystals with angstrom resolution on a subsecond timescale.
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