Understanding and Predicting Reactivity and Selectivity of Single Atom Catalyst

中佛罗里达大学的塔拉特·S·拉赫曼教授和刘福东教授以及布鲁顿·帕克学院的桑比奥·洪教授获得了化学系化学催化项目的支持，以了解和预测单原子催化剂的性质。在学术和工业化学实验室中使用催化剂来加速化学反应，同时选择特定的产品。单原子催化剂通常由纳米颗粒组成--十亿分之一米。纳米粒子具有独特的性质，由于它们的尺寸和限制较小，因此它们与它们的块体同行不同。例如，散装金是一种惰性材料，但以纳米颗粒的形式存在，它与空气中的气体(如一氧化碳)具有很强的反应性。纳米颗粒的微小尺寸也意味着贵金属成本的降低。在过去的十年里，人们对纳米催化剂进行了大量的研究，这些催化剂的局部环境可以控制到单个原子(通常是在支持性表面)。在纳米催化剂中，控制反应性和产物选择性的因素尤其令人感兴趣。在这个项目中，Rahman教授、Hong教授和Liu教授共同开展了在单分散的铂、铜和钴纳米粒子催化剂上氧化(受控燃烧)甲醇生成二氧化碳和分子氢的计算和实验研究。理论和实验之间的系统耦合有助于为合理设计具有所需反应活性和选择性的单原子催化剂提供指导。拉赫曼教授利用她作为美国物理学会桥梁项目UCF站点负责人的身份，指导来自参与该项目的代表性较低的少数群体的研究生。现有的国际合作有助于将成果扩展到全球。布鲁顿-帕克学院的本科生积极从事化学研究，为学术或行业的职业生涯积累了有用的经验。该项目预计将产生预测和控制原子分散的纳米催化剂的反应性的策略，作为其本地原子环境的函数。研究内容包括：热力学辅助、基于密度泛函理论(DFT)的电子和几何结构、振动动力学和熵、反应路径和能量学的计算；以及反应速率和翻转频率的动力学蒙特卡罗模拟，作为环境温度和压力的函数；单原子催化剂的合成。研究小组将使用扫描透射式电子显微镜(STEM)来确认目标系统的单点状态。博士后和研究生将进行甲醇部分氧化反应速率和周转频率的实验测定，以及原位漫反射红外傅里叶变换光谱(DRIFTS)的研究，以验证表面反应中间体和追踪反应机理。理论和实验齐头并进提供了对反应机理的理解，并对控制位置活动的电荷转移、应变等因素有了深入的了解。更重要的是，负责产品选择性的竞争反应路径(和反应中间体)被暴露，从而提供设计控制。计算和观测的表面结构、反应速率和周转频率之间的直接反馈验证了理论方法并改进了实验参数。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。

Professors Talat S Rahman and Fudong Liu of the University of Central Florida (UCF) and Professor Sampyo Hong of Brewton Parker College are supported by an award from the Chemical Catalysis program in the Division of Chemistry to understand and predict the properties of single atom catalysts. Catalyst are used in academic and industrial chemical laboratories to speed up chemical reactions while selecting for specific products over others. Single atom catalysts are often made of nanoparticles - a billionth of a meter. Nanoparticles have unique properties which distinguish them from their bulk counterparts because of their reduced size and confinement. For example, bulk gold is an inert material, but in nanoparticle form it be very reactive with gases in the air (like carbon monoxide). The miniscule size of the nanoparticles also means reduced cost of the precious metal. The last decade has seen much research on nanocatalysts whose local environment can be controlled down to the single atom (usually on a supportive surface). The factors that control reactivity and product selectivity are of particular interest in nanocatalysts. In this project, Professors Rahman, Hong and Liu carry out joint computational and experimental studies of oxidizing (burning in a controlled way) methanol to form carbon dioxide and molecular hydrogen on singly-dispersed platinum, copper, and cobalt nanoparticle catalysts. The systematic coupling between theory and experiment helps set guidelines for the rational design of single atom catalysts with desired reactivity and selectivity properties. Professor Rahman leverages her position as the UCF site leader for the American Physical Society Bridge Program to mentor the graduate students from underrepresented minority groups that work on the project. Existing international collaborations help extend the outcomes globally. Undergraduate students at Brewton-Parker College are actively engaged in chemistry research, gaining useful experience for careers in academics or industry. This project is expected to result in strategies for predicting and controlling the reactivity of atomically dispersed nanocatalysts, as a function of their local atomic environment. Research components include: thermodynamics-assisted, density functional theory (DFT)-based calculations of electronic and geometric structure, vibrational dynamics and entropy, reaction pathways and energetics; and kinetic Monte Carlo simulations of reaction rates and turn over frequencies, as a function of ambient temperature and pressure; synthesis of the single atom catalysts. The research team will use scanning transmission electron microscopy (STEM) to confirm the single site status of targeted systems. Postdocs and graduate students will conduct an experimental determination of methanol partial oxidation reaction rates and turnover frequencies as well as studies of in situ diffuse reflectance infra-red Fourier transform spectroscopy (DRIFTS) to verify surface reactive intermediates and track reaction mechanisms. Theory and experiment working in tandem provide an understanding of reaction mechanisms and insights into factors such as charge transfer, strain, etc. that control site activity. More importantly, competing reaction pathways (and reaction intermediates) responsible for product selectivity are exposed, thereby providing a design control. A direct feedback between calculated and observed surface structure, reaction rates and turnover frequencies validates the theoretical approach and refines experimental parameters.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.