Chemical and Structural Consequences of High Oxygen Coverages and Subsurface Oxygen in Catalytically Active Metals

催化作用对技术进步至关重要，尤其是在化学工业中。有机化学品在金属表面的部分氧化（催化剂）是一种应用广泛的催化反应。然而，这些看似简单的氧化反应的原子级细节仍然难以捉摸。金属表面的许多方面都是影响其反应性的因素。其中，金属原子的排列和各种含氧物质的丰度起着关键作用。在这个项目中，芝加哥洛约拉大学（LUC）的Dan Killelea博士和他的研究小组正在研究这些金属催化剂的表面结构和反应性在反应条件下的变化。值得注意的是，该项目还研究了地下氧，即溶解在固体催化剂近表层的氧原子。虽然表面下的氧原子本身可能不是反应物，但它们可能以重要的方式影响表面的反应性和性质。虽然表面化学研究是该提案的核心，但该项目扩大了对芝加哥公立学校（CPS）科学推广工作的参与。该项目的目标之一是支持社会经济地位不足的学生发展他们对科学事业的兴趣。通过这个项目，LUC的学生与CPS的学生在几个方面进行互动：高中实验室，参观LUC设施，以及暑期实习计划。额外的参与和推广工作包括与当地大学的招生顾问举办CPS学生会议，以及前往阿贡国家实验室。芝加哥洛约拉大学（Loyola University Chicago）的Dan Killelea博士在化学部化学催化项目的资助下，通过研究地下氧在三种催化金属（铑、钯和铂）中的形成以及物理和化学效应，正在推进对地下氧在金属中的行为的理解。在每一种情况下，地下氧被认为有助于催化过程的选择性，但其活性的来源仍不清楚。测量了不同氧丰度金属的反应性，并结合表面科学技术对地下氧的形成进行了量化。利用扫描隧道显微镜（STM）直接观察了氧化金属表面结构的变化。除了STM图像外，密度泛函理论（DFT）还用于识别这些金属表面和表面下氧原子的稳定结构及其影响。STM获得的数据与其他表面科学测量相补充。同时，这些方法提供了含地下氧金属表面的整体平均物理和化学性质的详细图像。该项目的结果通过提供急需的关于地下氧的基本信息，并揭示了它在工业相关的多相催化反应中的重要性，从而推进了表面催化。此外，来自美国国家科学基金会的支持加强了与荷兰、塔尔萨和芝加哥的研究人员的积极合作，以及对芝加哥当地公立高中的推广工作。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Catalysis is essential to technological advances, especially in the chemical industry. Partial oxidation of organic chemicals on metal surfaces (catalysts) is an extensively used catalytic reaction. However, the atomic-level details of these seemingly straightforward oxidation reactions have remained elusive. Many aspects of the metal surface factor in to its reactivity. Among them, the arrangements of metal atoms, and the abundance of various oxygen-containing species, play key roles. In this project, Dr. Dan Killelea of Loyola University Chicago (LUC) and his research group are studying how the surface structures and reactivity of these metal catalysts change under reaction conditions. Significantly, this project also examines subsurface oxygen, which are oxygen atoms dissolved into the near-surface layers of the solid catalysts. Although subsurface oxygen atoms may not be reactants themselves, they may affect the reactivity and properties of the surface in important ways. While surface chemistry research is central to this proposal, this project broadens participation in science outreach efforts to the Chicago Public Schools (CPS). One goal of this project is to support students of under-represented socioeconomic status to develop their interest in scientific careers. Through this project, LUC students engage CPS students in several contexts: the high school lab, tours of LUC facilities, and a Summer Internship Program. Additional engagement and outreach efforts include hosting CPS student meetings with admissions counselors from local universities, and trips to Argonne National Laboratory. With funding from the Chemical Catalysis Program of the Chemistry Division, Dr. Dan Killelea of Loyola University Chicago is advancing the understanding of the behavior of subsurface oxygen in metals by investigating its formation, and physical and chemical effects in three catalytic metals: rhodium, palladium, and platinum. In each, subsurface oxygen is thought to contribute to the selectivity of catalytic processes, but the origins of their activity remain unclear. The reactivity of the metals with various oxygen abundances is measured and the formation of subsurface oxygen is quantified with a combination of surface science techniques. The changes in the surface structures of the oxidized metals are directly observed using Scanning Tunneling Microscopy (STM). In addition to the STM images, density functional theory (DFT) is used to identify stable structures of surface and subsurface oxygen atoms on these metals and their effects. The data obtained with STM is complemented with other surface science measurements. In concert, these provide a detailed picture of the ensemble-averaged physical and chemical properties of metal surfaces with subsurface oxygen. The results of this project advance surface catalysis by providing much needed fundamental information about subsurface oxygen and reveal the importance of it in industrially relevant heterogeneously catalyzed reactions. Additionally, support from the NSF strengthens active collaborations with researchers in The Netherlands, Tulsa, and Chicago, as well as outreach efforts to local Chicago Public High Schools.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.