Characterization of nanometer-sized particles dispersed onto a porous support is critical for understanding performance of heterogenous catalysts. The electron microscope offers a unique capability for measuring the cluster size and chemistry of these nanometer-sized metal clusters. Cluster size and size distribution can be readily determined by using high angle annular darkfield or z-contrast microscopy. However, as catalysts become more complex with additional components that modify the metal activity, determination of the chemistry of individual clusters could be interesting. Conducting such studies is not straightforward and some of the problems associated with making such measurements will be discussed using model catalysts and a VG HB 601UX dedicated STEM.

Problems associated with this type of measurement can include the instability of the small metal particle under the intense, focused electron beam as well as spurious signals from the area surrounding the region of interest.