Direct In Situ TEM Visualization and Insight into the Facet‐Dependent Sintering Behaviors of Gold on TiO₂

Abstract

Preventing sintering of supported nanocatalysts is an important issue in nanocatalysis. A feasible way is to choose a suitable support. However, whether the metal–support interactions promote or prevent the sintering has not been fully identified. Now, completely different sintering behaviors of Au nanoparticles on distinct anatase TiO2 surfaces have been determined by in situ TEM. The full in situ sintering processes of Au nanoparticles were visualized on TiO2 (101) surface, which coupled the Ostwald ripening and particle migration coalescence. In contrast, no sintering of Au on TiO2 anatase (001) surface was observed under the same conditions. This facet‐dependent sintering mechanism is fully explained by the density function theory calculations. This work not only offers direct evidence of the important role of supports in the sintering process, but also provides insightful information for the design of sintering‐resistant nanocatalysts.

In‐situ Transmission Electron Microscope Techniques for Heterogeneous Catalysis

“…Scientists have tried to develop methods to reduce the thickness of the liquid layer to improve the image quality. [118] sintering behaviors of Au on TiO 2 Hitachi H-9500/Protochips HRTEM, HAADF-STEM [119] metal-support interaction of catalysts JEOL3100-R05/Protochips atmosphere system EELS, HAADF-STEM [120] CO 2 hydrogenation to methanol JEM-ARM300F/DENSsolutions HRTEM [121] liquid synthesis of Au hollow catalysts Titan Themis, FEI/Protochips HADDF-STEM, EDX, TEM [112] synthesis of metal-organic catalysts JEOL ARM300F/Protochips Poseidon Select HAADF-STEM, EDX, TEM [56] liquid, light water splitting by TiO 2 Titan G2 60-300 and JEOL-2010F (with optical fiber inside)/homemade liquid holder TEM, EELS, EDX, HAADF-STEM [122] gas, heating, light photocatalysis Tecnai F20, FEI (with optical fiber inside)/Gantan hot stage HRTEM, EELS, XPS [123] Figure 16. In-situ TEM images of Au/MgO at different water vapor pressures (10 À 5 Pa and 10 À 4 Pa) under different electron doses (10 À 15 A/nm 2 and 10 À 14 A/nm 2 ).…”

New Strategies for the Preparation of Sinter‐Resistant Metal‐Nanoparticle‐Based Catalysts

“…d) Sintering behavior of Au NPs on TiO 2 (101) surface. Reproduced with permission . Copyright 2018, Wiley‐VCH.…”

“…In addition, the migration‐coalescence process was also proposed to cause the metal sintering, which involves in Brownian mention of metal nanoparticles on the catalyst surface, leading to the formation of larger particles when the small particles come in close proximity to each other. Yuan et al investigated the Au sintering on titania surface by in situ transmission electron microscopy (TEM) characterization with low electronic pressure to minimize the influence of electron beam, where the small nanoparticle migration and coalescence were directly observed to form the large particles (Figure d). Then the large particles further sintered with the small particles nearby via the Ostwald ripening, confirming that the different mechanism simultaneously occurred in the nanoparticle sintering of one sample.…”

In Situ Transmission Electron Microscopy on Energy‐Related Catalysis

“…Yuan et al reported sintering behaviors of Au nanoparticles on distinct TiO 2 surfaces under oxygen gas environments. The Au nanoparticles on the TiO 2 (101) surface migrated together and became a large particle corresponding to the Ostwald ripening mechanism.…”

“…The images are acquired at 500 °C and the oxygen pressure is ≈3.75 × 10 −4 Torr. Reproduced with permission . Copyright 2018, Wiley‐VCH.…”