LAUSR

Oxygen exchange on CeO2 (ceria) nanoparticle surfaces is often the rate limiting step in technological applications [1], and a nanoparticle’s shape, size, surface composition, and surface atomic arrangement can all influence catalytic activity, meaning that each individual nanoparticle may have its own intrinsic chemical and physical properties. Consequently, the ability to accurately and quantitatively characterize nanocatalysts to locate ‘active’ sites is necessary to understand and tailor their behavior. In addition to differentiating between the functionally-relevant active structures and the passive spectator structures on a catalyst, the structural motifs may change during a single ‘turnover’ event of a chemical reaction [2]. An accurate description of a nanoparticle’s surface structure therefore requires a technique that combines atomic spatial resolution with sensitivity to changes in the structure during a reaction. Advances in aberration-corrected TEM (AC-TEM) have vastly improved image resolution and quality, and the recent development of direct electron detectors has led to significantly improved performance in read-out speed and noise reduction over CCD imaging cameras [3]. Here, we demonstrate the use of in situ time-resolved AC-TEM on a CeO2 nanoparticle to directly observe dynamic surface reconstructions with atomic spatial resolution and 2.5 ms time resolution.