| AVS 63rd International Symposium & Exhibition | |
| In-Situ and Operando Spectroscopy and Microscopy for Catalysts, Surfaces, & Materials Focus Topic | Thursday Sessions |
| Session IS-ThA |
| Session: | Ambient Pressure Photoelectron Spectroscopy and Scanning Probe Techniques |
| Presenter: | Miaofang Chi, Oak Ridge National Laboratory |
| Authors: | M. Chi, Oak Ridge National Laboratory C. Wang, Johns Hopkins University K. More, Oak Ridge National Laboratory Y. Xia, Georgia Institute of Technology |
| Correspondent: | Click to Email |
The catalytic performance of nanocatalysts in terms of activity, selectivity, and durability, is primarily determined by the precise nature of the surface and near-surface atomic configurations. The surface atomic arrangements of nanoparticles (NPs), both in structure and chemistry, however, are highly dynamic during synthesis treatments and reaction conditions. Precisely understanding the complete evolution of NPs as a function of synthesis and reaction environments is imperative towards the rational design of nanocatalysts with optimized performance. With the ability of chemical-sensitive imaging at atomic resolution and the simultaneous acquisitions of electron energy loss spectroscopy (EELS) and energy dispersive X-ray (EDX) analysis, in situ scanning transmission electron microscopy (STEM) plays an important role in such studies. In this presentation, we will demonstrate how atomic-scale surface arrangements respond dynamically to in situ thermal annealing and gas reaction conditions in bi-metallic nanocatalysts. In particular, by tracking the same individual NPsduring in situ annealing, the influence of post-synthesis treatments on Pt3Co NPs will be discussed. Five distinct stages of surface elemental rearrangements are discerned at the atomic scale: initial random (alloy) elemental distribution; surface Pt-skin-layer formation; nucleation of structurally ordered domains; ordered framework development; and finally, initiation of amorphization. Furthermore, the responses of surface atomic configurations in alloyed Pd-Au NPs to different reactive environments, including both reducing and oxidizing gases, will be discussed. In both cases, comprehensive interplays among phase evolution, surface faceting, and elemental inter-diffusion are revealed.
Acknowledgements: This work was supported by the Center for Nanophase Materials Sciences, which is U. S. Department of Energy Office of Science User Facility.