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In Scanning Electron Microscopy (SEM) a finely focused beam of electrons is scanned across the surface of the subject, and reflected electrons are detected, allowing an image to be built up. Focusing is achieved using electromagnetic "lenses".
The maximum resolution of the technique is limited by the spot size that can be produced with the electron beam. With modern microscopes it is possible to show features as small as 5nm.
This makes it possible to "see" minute metal particles, such as platinum, within supported catalysts, and enables researchers to discover if particles join together to form larger units under reaction conditions. It is possible to relate this change in metal particle size to catalyst activity.











The Department of Inorganic Chemistry at the Fritz Haber Institute in Berlin has looked at the effect of "milling" on vanadium pentoxide catalyst (used in the Contact Process for the manufacture of sulphuric acid). Milling, essentially grinding the material, is known to make the catalyst more effective by increasing the surface area available, but the SEM images clearly show how longer milling times result in the particles beginning to recombine. Other effects of milling were investigated using other techniques.


Scanning Electron Microscopy