Su Hai-Sheng, Feng Hui-Shu, Zhao Qing-Qing, Zhang Xia-Guang, Sun Juan-Juan, He Yuhan, Huang Sheng-Chao, Huang Teng-Xiang, Zhong Jin-Hui, Wu De-Yin, Ren Bin
Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering , Xiamen University , Xiamen 361005 , China.
Collaborative Innovation Center of Henan Province for Green Manufacturing of Fine Chemicals, Key Laboratory of Green Chemical Media and Reactions, Ministry of Education, School of Chemistry and Chemical Engineering , Henan Normal University , Xinxiang , Henan 453007 , China.
J Am Chem Soc. 2020 Jan 22;142(3):1341-1347. doi: 10.1021/jacs.9b10512. Epub 2020 Jan 10.
Active oxygen species (AOS) play key roles in many important catalytic reactions relevant to clean energy and environment. However, it remains challenging to characterize the active sites for producing AOS and to image the surface properties of AOS, especially on multicomponent metallic catalyst surfaces. Herein, we utilize tip-enhanced Raman spectroscopy (TERS) to probe the local generation and diffusion of OH radicals on a Pd/Au(111) bimetallic catalyst surface. The reactive OH radicals can be catalytically generated from hydrogen peroxide (HO) at the metal surface, which then oxidizes the surface adsorbed thiolate, a reactant that is used as the TERS probe. By TERS imaging of the spatial distribution of unreacted thiolate molecules, we demonstrate that the Pd surface is active for generation of OH radicals and the Pd step edge shows much higher activity than the Pd terrace, whereas the Au surface is inactive. Furthermore, we find that the locally generated OH radicals at the Pd step edge could diffuse to both the Au and the Pd surface sites to induce oxidative reactions, with a diffusion length estimated to be about 5.4 nm. Our TERS imaging with few-nanometer spatial resolution not only unravels the active sites but also characterizes in real space the diffusion behavior of OH radicals. The results are highly valuable to understand AOS-triggered catalytic reactions. The strategy of using reactants with large Raman cross sections as TERS probes may broaden the application of TERS for studying catalysis with reactive small molecules.
活性氧物种（AOS）在许多与清洁能源和环境相关的重要催化反应中起着关键作用。然而，表征产生AOS的活性位点以及描绘AOS的表面性质仍然具有挑战性，特别是在多组分金属催化剂表面上。在此，我们利用针尖增强拉曼光谱（TERS）来探测Pd/Au(111)双金属催化剂表面上OH自由基的局域生成和扩散。活性OH自由基可以在金属表面由过氧化氢（HO）催化生成，然后氧化表面吸附的硫醇盐，硫醇盐作为一种反应物被用作TERS探针。通过对未反应硫醇盐分子空间分布的TERS成像，我们证明Pd表面对OH自由基的生成具有活性，并且Pd台阶边缘比Pd平台显示出更高的活性，而Au表面则无活性。此外，我们发现Pd台阶边缘处局域生成的OH自由基可以扩散到Au和Pd表面位点以引发氧化反应，扩散长度估计约为5.4 nm。我们具有几纳米空间分辨率的TERS成像不仅揭示了活性位点，还在真实空间中表征了OH自由基的扩散行为。这些结果对于理解AOS引发的催化反应具有很高的价值。使用具有大拉曼截面的反应物作为TERS探针的策略可能会拓宽TERS在研究与活性小分子相关的催化作用方面的应用。
