Tracking Reaction Surfaces: Gold becomes a remarkably active catalyst for CO oxidation when it is dispersed as nanoparticles on the surface of reducible metal oxides such as ceria, so much so that the reaction proceeds at room temperature. Yoshida et al. (p. 317 ) used an aberration-corrected, environmental transmission electron microscope to follow the changes in both ceria-supported gold nanoparticles and the adsorbed species for this reaction.

Although available since the early days of electron microscopy, recent technology developments of the environmental transmission electron microscope (ETEM) have enabled new research in the study of nanomaterials in gaseous environments. Significant improvements in scanning/transmission electron microscope (S/TEM) technologies, while containing a gaseous environment close to the object under investigation, enable now the atomic scale study of phenomena occurring during gas–solid interactions. A focus behind these developments is the research on nanomaterial-based technologies, for instance for efficient energy conversion, use and storage as well as for environmental protection. In situ high spatial resolution characterization provides unique information that is beneficial for understanding the relationship between the structure, properties and function of nanostructures directly on their characteristic length scales. The progress in recent research is reviewed to highlight the potential of the state-of-the-art differentially-pumped microscope platform, based on the latest microscope generation optimized for atomic scale in situ investigations. Using cases from current catalysis research, high resolution imaging reveals structural changes in nanocatalysts when being active and is instrumental in understanding deactivation processes; while spectroscopy gives additional access to reactivity. Also, imaging schemes are discussed that focus on enhancing the achievable imaging resolution, while having the effect of electron beam–solid interaction in the nanomaterial under control.