Simultaneous 2D Projection and 3D Topographic Imaging of Gas-Dependent Dynamics of Catalytic Nanoparticles

Abstract

Catalyst deactivation through pathways such as sintering of nanoparticles and degradation of the support is a critical factor when designing high-performance catalysts. Here, structural changes of supported nanoparticle catalysts are investigated in controlled gas environments (O 2 , H 2 O, and H 2 ) at different temperatures by imaging simultaneously the nanoparticle structures in 2D projection and the 3D surface-sensitive topography. Platinum nanoparticles on carbon support as a model system are imaged in an environmental transmission electron microscope (ETEM), with concurrent acquisition of high-angle annular dark field scanning TEM (HAADF-STEM) and secondary electron (SE) images. Particle migration and coalescence occurs and shows gas-dependent kinetics, with nanoparticles moving across and through the support during and after coalescence. The temperature required for motion is lower in O 2 than in H 2 O and H 2 , explained through the nature of the gas/nanoparticle interactions. In O 2 and H 2 , the carbon support degrades by trench formation along migration pathways, and the particles move continuously, indicating a chemical reaction between gas and support. In H 2 O gas, motion is more discontinuous and oriented particle attachment occurs, as expected from theoretical predictions. These results suggest that multimodal imaging in ETEM that combines HAADF-STEM and SE data provides comprehensive information regarding catalyst dynamics and degradation mechanisms.