  Heterogeneous catalysts are the most important catalysts in industrial
reactions. Nanocatalysts, with size ranging from hundreds of nanometers to the
atomic scale, possess activities that are closely connected to their structural
characteristics such as particle size, surface morphology, and
three-dimensional topography. Recently, the development of advanced analytical
transmission electron microscopy (TEM) techniques, especially quantitative
high-angle annular dark-field (HAADF) imaging and high-energy resolution
spectroscopy analysis in scanning transmission electron microscopy (STEM) at
the atomic scale, strengthens the power of (S)TEM in analyzing the
structural/chemical information of heterogeneous catalysts. Three-dimensional
reconstruction from two-dimensional projected images and the real-time
recording of structural evolution during catalytic reactions using in-situ
(S)TEM methods further broaden the scope of (S)TEM observation. The
atomic-scale structural information obtained from high resolution (S)TEM has
proven to be of significance for better understanding and designing of new
catalysts with enhanced performance.
