CAS: Functional Nanoglues for Robust and Efficient Single-Atom Catalysis

新的催化转化工艺可能对全球能源安全产生重大影响，并带来更清洁的环境。许多化学制造和排放控制过程使用贵金属作为催化剂来加速化学反应。贵金属在工业催化剂中的使用是不可持续的，因为这些金属的丰度低，成本高。使用负载单金属原子进行催化转化可以解决这些问题。单原子催化剂广泛应用的关键挑战是它们在使用过程中的稳定性。在这个项目中，亚利桑那州立大学的刘晶月(Jimmy)博士正在开发既能稳定担载的单金属原子又能增强其催化性能的纳米胶体。该项目致力于解决对负载型金属原子催化的基本理解，并为开发对环境和经济具有重要实际应用的单原子催化剂提供设计工具。刘教授通过亚利桑那州立大学冬季高分辨率电子显微镜学校影响教育，主要由研究生参加。此外，科学和工程体验(场景)计划正在为10-12年级的高中生提供尖端科学研究体验。在化学系化学催化项目的资助下，亚利桑那州立大学的刘静月(Jimmy)博士正在发展关于如何通过将单个金属原子(如铂、钯、Rh、Ru、Ir或Au)限制在孤立的超小功能氧化物纳米团簇(如CeOx、TiOx和CoOx)中来定位并同时增强其催化性能的基础知识。这些纳米胶体均匀地嫁接到高比表面积的坚固载体上(例如，二氧化硅或氧化铝)。通过这样的催化剂设计，预计单个金属原子或小金属团簇在催化剂活化过程中(例如，在250℃-500℃下被H2)和/或在还原环境下的高温催化反应期间不会烧结。使用负载型、孤立的金属原子作为催化活性中心，不仅可以最大限度地提高金属的利用效率，而且可以使活性中心均匀分布。这些因素对于调节目标催化反应的选择性非常重要。催化剂设计允许金属原子在相应的孤立纳米胶岛内移动，但不能越过纳米胶体形成更大的颗粒。这种纳米胶体不仅起到了“双面胶带”的作用，牢固地固定了金属原子和高比表面积的载体，而且还为目标催化活性和/或选择性提供了所需的功能。纳米胶岛的尺寸范围为0.5-2.0 nm，以适应高水平的金属负载。对纳米胶基单原子催化剂进行了CO氧化、CO优先氧化、水-气变换、重整和加氢/脱氢反应的测试。更广泛的影响包括将研究成果纳入每年一度的高分辨率电子显微镜冬季研讨会(主要由来自美国各地的研究生参加)，培训研究生和本科生，并通过致力于为10-12年级的高中生提供尖端科学研究体验的科学和工程体验(SCEAM)计划指导高中生。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。

New catalytic conversion processes may significantly impact global energy security and lead to a cleaner environment. Many chemical manufacturing and emission control processes use precious metals as catalysts to speed up the chemical reactions. The use of precious metals in industrial catalysts is not sustainable because of the low abundance and high cost of these metals. The use of supported single metal atoms for catalytic transformation may address these problems. The critical challenge for broad applications of single-atom catalysts is their stability during use. In this project, Dr. Jingyue (Jimmy) Liu of Arizona State University is developing "nanoglues" to both stabilize the supported single metal atoms and enhance their catalytic performance. This project is addressing fundamental understanding of catalysis by supported metal atoms and is providing design tools for developing single atom catalysts with practical applications important to the environment and the economy. Professor Liu impacts education through the ASU Winter School on High Resolution Electron Microscopy, attended primarily by graduate students. In addition, the SCience and ENgineering Experience (SCENE) program is providing cutting-edge science research experiences to high school students in grades 10-12. With funding from the Chemical Catalysis Program of the Division of Chemistry, Dr. Jingyue (Jimmy) Liu of Arizona State University is developing a fundamental understanding of how to localize, and simultaneously enhance the catalytic properties of, single metal atoms (e.g., Pt, Pd, Rh, Ru, Ir or Au) by confining them to isolated, ultra-small functional oxide nanoclusters (e.g., CeOx, TiOx, and CoOx). These nanoglues are uniformly grafted onto a high-surface-area robust support (e.g., silica or alumina). With such a catalyst design, it is expected that single metal atoms or small metal clusters do not sinter during the catalyst activation process (e.g., by H2 at 250 C - 500 C) and/or during catalytic reactions at elevated temperatures under reducing environment. The use of supported, isolated metal atoms as catalytically-active centers not only maximizes the metal usage efficiency but also makes it possible to have uniform distribution of active sites. These factors are important for tuning the selectivity of a targeted catalytic reaction. The catalyst design allows metal atoms to move within their corresponding isolated nanoglue islands but not across the nanoglues to form larger particles. The nanoglue not only acts as a “double-sided tape” to strongly hold both the metal atoms and the high-surface-area support but also provides the desired function for the targeted catalytic activity and/or selectivity. The sizes of the nanoglue islands range 0.5-2.0 nm to accommodate high levels of metal loading. The nanoglue-based single-atom catalysts are being tested for CO oxidation, preferential oxidation of CO, water-gas shift, reforming, and hydrogenation/dehydrogenation reactions. Broader impacts include incorporating research results in an annual Winter Workshop of High Resolution Electron Microscopy (attended primarily by graduate students from across the US), training of graduate and undergraduate research students, and mentoring of high school students through the SCience and ENgineering Experience (SCENE) program dedicated to providing cutting-edge science research experiences to high school students in grades 10-12.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.