Collaborative Research: Directly probing the local coordination, charge state and stability of single atom catalysts – Critical insights from advanced TEM for promoting stability

对性能精心控制的原子效率催化剂的推动推动了单原子催化剂（SAC）的发展，其中单个贵金属原子稳定在高表面积载体上。 SAC 在从汽车催化到电催化的化学过程中表现出独特且潜在有用的特性。 然而，有关载体上金属结合位点的结构及其在反应条件下的稳定性的信息很少。这是由于缺乏对金属种类的均匀性及其迁移率的了解，而通过样本平均测量来评估这些均匀性具有挑战性。研究人员将克服这些限制，通过将最先进的原子分辨率透射电子显微镜和光谱学与仔细的催化剂合成和样品平均分析相结合，获得对 SAC 工作状态的原子尺度和定量见解。该研究将重点关注更有效地利用昂贵且稀缺的贵金属的催化剂设计，从而为更高效、更经济的化学制造和环境修复技术打开大门。该研究与教育和外展活动相结合，以吸引不同的初级科学家，包括女性和代表性不足的少数群体，并培训未来的领导者以应对关键的社会挑战。该项目利用加州大学欧文分校 (UCI) 独特的电子显微镜设施以及加州大学圣巴巴拉分校 (UCSB) 最先进的催化剂合成和光谱表征能力。 该研究的中心目标是利用先进的非原位和原位像差校正扫描透射电子显微镜和相关的电子能量损失光谱来探测SAC的局部配位、金属电荷状态和稳定性，并将这些特性与原位红外光谱的光谱分析相关联。 SAC 的研究极大地受益于原位亚埃分辨率成像，因为这提供了解释样本平均测量中的光谱数据所需的特定位点信息。该项目重点研究氧化铝（由原子分散的铼和钨改性）、二氧化钛和二氧化铈上的 Pt、Rh 和 Au SAC，它们呈现出金属氧化态、载体还原性和可用结合位点的变化。这些系统的详细表征使得能够设计出具有针对CO氧化、NO还原和烯烃加氢甲酰化等催化过程的调节反应性和稳定性的新型催化剂。将研究与学生教育和培训相结合，使该项目的成果能够在本科生课程作业和实习期间传播给 UCI 和 UCSB 的不同学生群体，并通过暑期学校项目传播给来自不同背景的高中生，这将提高他们对科学研究和教育的兴趣。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

The drive for atom-efficient catalysts with carefully controlled properties has motivated the development of single atom catalysts (SACs), where single precious metal atoms are stabilized on high-surface-area supports. SACs exhibit unique and potentially useful characteristics for chemical processes ranging from automotive catalysis to electrocatalysis. However, information about the structure of the metal binding site on the support and its stability under reaction conditions is sparse. This is due to a lack of insights into the uniformity of metal species and their mobility, which are challenging to assess from sample-averaged measurements. The investigators will overcome these limitations to obtain atomic-scale and quantitative insights into the working state of SACs by coupling state-of-the-art atomic resolution transmission electron microscopy and spectroscopy with careful catalyst synthesis and sample averaged analyses. The study will focus on the design of catalysts that utilize expensive and scarce noble metals more effectively, thus opening the door to more efficient and economical chemical manufacturing and environmental remediation technologies. The research is integrated with education and outreach activities to attract diverse junior scientists, including women and underrepresented minority groups, and train future leaders to address critical societal challenges.The project leverages unique electron microscopy facilities at the University of California-Irvine (UCI) with state-of-the-art catalyst synthesis and spectroscopic characterization capabilities at the University of California-Santa Barbara (UCSB). The central objectives of the research are to utilize advanced ex situ and in situ aberration-corrected scanning transmission electron microscopy and associated electron energy loss spectroscopy to probe the local coordination, metal charge state, and stability of SACs and correlate these properties to spectroscopic analysis by in situ infrared spectroscopy. The study of SACs benefits significantly from in situ sub-angstrom resolution imaging, as this provides site-specific information needed to interpret spectroscopic data from sample averaged measurements. This project focuses on Pt, Rh, and Au SACs on alumina (modified by atomically-dispersed Re and W), titania, and ceria which present variations in metal oxidation-state, support-reducibility, and available bindings sites. Detailed characterization of these systems enables the design of new catalysts with tuned reactivity and stability for catalytic processes such as CO oxidation, NO reduction, and alkene hydroformylation. The integration of the research with education and training of students allows the results from this project to be disseminated to the diverse student populations of UCI and UCSB during coursework and internships for undergraduate students, as well as to high school students from diverse backgrounds through summer school programs, which will promote their interest in scientific research and education.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.