New Strategies for Creating Single and Dual Atom Catalysts on Silica Surfaces

催化剂使反应进行得更快，并产生更多所需的产品。没有催化剂，工业化学就不可能实现。然而，在催化剂的可持续使用和回收方面仍然存在巨大的挑战。一个最佳的催化剂应该只由一个或两个原子组成，这些原子被阻止聚集在一起形成大束(聚集体)。这种原子的分离可以通过将原子排列在表面上并将它们保留在其特定的表面位置来实现。在这个项目中，德克萨斯农工大学的珍妮特·布鲁梅尔教授正在利用两项早期的发现来实现这一目标。首先，在二氧化硅等表面上放置一层定义明确的金属络合物(单层)。然后，金属络合物被修饰，形成单个原子，这些原子保持在原位，分散在表面上。同样，双原子组装也是从含有两个不同金属中心的金属络合物中制备出来的，这些金属中心结合在表面上。Bluemel教授的团队正在探索这些单原子和双原子催化剂的催化活性，它们选择性形成产品的能力，以及它们的可回收性。不同的分析方法正在被使用和改进，以更好地了解表面过程，并最终产生更高效、具有更好特性的催化剂。该项目正在加强关于如何创造定义明确的、有效的、可回收的催化剂的基本知识，并正在导致更可持续的过程。该项目还在Bluemel教授的实验室为本科生和研究生提供广泛、深入的培训。特别是，学生们有机会与国内和国际的化学公司直接互动，从而获得独特和有益的工业经验。在化学系化学催化计划的资助下，德克萨斯农工大学的珍妮特·布鲁梅尔教授正在研究二氧化硅表面的动态过程，其中包括负载的分子镍、钯和铜的络合物。通过使用连接物将络合物连接到表面来支持物种。被束缚的物种被用作前体，故意在二氧化硅等表面上生成定义良好的单金属原子和双金属原子催化剂。只有当共价固定化催化剂悬浮在溶剂中时，动态过程才会发生。Bluemel研究小组发现，即使在没有溶剂的情况下，通过范德华相互作用吸附的金属络合物在孔内的表面也显示出不同的迁移率模式。目前，对催化剂及其前体如何在悬浮液中或干燥表面扩散有一个初步的了解。该项目的最终目标是利用特定的三齿膦连接体的影响和茂镍的干吸附，从而获得定义良好的单分子层，并探索在氧化物表面生成单原子和双原子催化剂(SACS，DAC)和定义良好的纳米颗粒的新方法。所有旨在稳定金属颗粒并防止其不受限制地生长的方法都只在表面上可行。研究分子固载和吸附的催化剂前体以及由它们生成的负载型活性金属催化剂，可以加深对它们的分解、团聚和金属颗粒形成的理解。对所有表面物种的结构和动力学的直接洞察是通过高分辨率透射电子显微镜、干物质的介磁和顺磁1H、2H、13C、29Si和31P魔角旋转核磁共振波谱以及其他技术提供的。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Catalysts allow reactions to proceed faster and to produce greater quantities of desirable products. Industrial chemistry would not be possible without the use of catalysts. However, big challenges remain regarding the sustainable use and recycling of catalysts. An optimal catalyst would consist of only one or two atoms that are prevented from grouping together and forming large bundles (aggregates). This separation of atoms can be achieved by arranging the atoms on a surface and retaining them at their specific surface sites. In this project, Professor Janet Bluemel of Texas A&M University is making use of two earlier discoveries to reach this goal. First, a well-defined one layer (monolayer) of metal complexes are placed on surfaces such as silica. The metal complexes are then modified to form single atoms that remain in place, dispersed on the surface. Similarly, two-atom assemblies are being prepared from metal complexes containing two different metal centers that are bound to the surface. Professor Bluemel's group is exploring the catalytic activities of these single- and dual-atom catalysts, their ability to form products selectively, and their recyclability. Different analytical approaches are being used and refined to obtain better insight into the surface processes and ultimately generate more efficient catalysts with superior characteristics. The project is enhancing the fundamental knowledge about how to create well-defined, efficient, recyclable catalysts in general and is leading to more sustainable processes. This project also provides broad, in-depth training for undergraduate and graduate students in Professor Bluemel's laboratory. In particular, the students are provided with opportunities for direct interaction with both domestic and international chemical companies, thus giving them unique and beneficial industrial experience.With funding from the Chemical Catalysis Program of the Chemistry Division, Professor Janet Bluemel of Texas A&M University is investigating dynamic processes on silica surfaces that involve supported molecular nickel, palladium, and copper complexes. The species are supported by tethering the complexes to the surface with the use of linkers. The tethered species are used as precursors to deliberately create well-defined single- and dual metal atom catalysts on surfaces such as silica. Dynamic processes do not occur only when covalently immobilized catalysts are suspended in a solvent. The Bluemel group has discovered that metal complexes adsorbed via Van der Waals interactions also display different modes of mobility on surfaces within pores, even in the absence of a solvent. At present there is a rudimentary understanding of how catalysts and their precursors diffuse in suspension or on dry surfaces. The ultimate goal of this project is to exploit the impact of specific tridentate phosphine linkers and the dry adsorption of nickelocene, which leads to well-defined monolayers, and to explore new methods for generating single- and dual atom catalysts (SACs, DACs) and well-defined nanoparticles on oxide surfaces. All approaches, which aim at stabilizing the metal particles and preventing their unrestricted growth are only feasible on surfaces. Investigating molecular immobilized and adsorbed catalyst precursors and the supported active metal catalysts generated from them, improves the understanding of their decomposition, agglomeration, and formation of metal particles. Direct insight regarding the structure and dynamics of all surface species is provided by High Resolution Transmission Electron Microscopy, dia- and paramagnetic 1H, 2H, 13C, 29Si, and 31P Magic Angle Spinning Nuclear Magnetic Resonance Spectroscopy of the dry materials and other techniques.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.