Liu Yukun, Koo Kunmo, Mao Zugang, Fu Xianbiao, Hu Xiaobing, Dravid Vinayak P
Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208.
International Institute of Nanotechnology, Northwestern University, Evanston, IL 60208.
Proc Natl Acad Sci U S A. 2024 Oct;121(40):e2408277121. doi: 10.1073/pnas.2408277121. Epub 2024 Sep 27.
Palladium (Pd) catalysts have been extensively studied for the direct synthesis of HO 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.
钯（Pd）催化剂已被广泛研究用于在环境条件下通过氢氧化反应直接合成过氧化氢。这种多相催化反应不仅具有相当大的实际意义，而且还是研究包括吸附质之间的吸附和反应在内的基本机制的经典模型。然而，在不同气体条件下其中间反应阶段的控制机制和动力学仍然难以捉摸。这归因于催化剂的吸附、原子扩散和并发相变之间的复杂相互作用。在此，通过气室透射电子显微镜对钯催化的生成水的氢氧化反应进行原位研究，以探究中间反应阶段。与可逆氢化钯形成相关的水生成动态行为以纳米级空间分辨率实时捕获。我们的研究结果表明，钯催化的氢氧化速率受气体引入顺序的显著影响。通过电子衍射和密度泛函理论计算的直接证据，我们证明氢氧化速率受前驱体吸附的限制。这些纳米级见解有助于确定钯催化氢氧化的最佳反应条件，这对水生产技术具有重要意义。所形成的认识还提倡对其他金属催化反应中的类似机制进行更广泛的探索。
