2024-10-01 ノースウェスタン大学
For the first time ever, researchers have witnessed — in real time and at the molecular-scale — hydrogen and oxygen atoms merge to form tiny, nano-sized bubbles of water. Video by Vinayak Dravid/Northwestern University
＜関連情報＞
- https://news.northwestern.edu/stories/2024/september/watch-water-form-out-of-thin-air/
- https://www.pnas.org/doi/10.1073/pnas.2408277121
- https://tiisys.com/blog/2024/01/20/post-132203/
パラジウム表面の吸着限界水素酸化反応を電子顕微鏡で解明 Unraveling the adsorption-limited hydrogen oxidation reaction at palladium surface via in situ electron microscopy
Yukun Liu, Kunmo Koo, Zugang Mao, +2, and Vinayak P. Dravid
Proceedings of the National Academy of Sciences Published:September 27, 2024
DOI:https://doi.org/10.1073/pnas.2408277121
Significance
Unraveling the reaction kinetics of Pd-catalyzed, water-forming hydrogen oxidation under various gas conditions has posed a considerable experimental challenge. In this study, we achieve nanoscale direct visualization of water formation from this reaction using gas cell transmission electron microscopy. We disentangle the intricate interplay between adsorption, atomic diffusion, and concurrent phase transformation of catalyst. The observed differences in water generation rates with varying gas supply sequences, corroborated by electron diffraction analysis, indicate that the rate of Pd-catalyzed hydrogen oxidation is limited by precursors adsorption. This understanding enables identifying the optimal catalytic reaction condition, holding substantial implications for applications in water generation. Furthermore, our findings advocate exploration of analogous mechanisms in other metal-catalyzed reactions.
Abstract
Palladium (Pd) catalysts have been extensively studied for the direct synthesis of H2O through the hydrogen oxidation reaction at ambient conditions. This heterogeneous catalytic reaction not only holds considerable practical significance but also serves as a classical model for investigating fundamental mechanisms, including adsorption and reactions between adsorbates. Nonetheless, the governing mechanisms and kinetics of its intermediate reaction stages under varying gas conditions remain elusive. This is attributed to the intricate interplay between adsorption, atomic diffusion, and concurrent phase transformation of catalyst. Herein, the Pd-catalyzed, water-forming hydrogen oxidation is studied in situ, to investigate intermediate reaction stages via gas cell transmission electron microscopy. The dynamic behaviors of water generation, associated with reversible palladium hydride formation, are captured in real time with a nanoscale spatial resolution. Our findings suggest that the hydrogen oxidation rate catalyzed by Pd is significantly affected by the sequence in which gases are introduced. Through direct evidence of electron diffraction and density functional theory calculation, we demonstrate that the hydrogen oxidation rate is limited by precursors’ adsorption. These nanoscale insights help identify the optimal reaction conditions for Pd-catalyzed hydrogen oxidation, which has substantial implications for water production technologies. The developed understanding also advocates a broader exploration of analogous mechanisms in other metal-catalyzed reactions.
