CAREER: Simulation of Metal Nanoparticle Interactions with Doped Carbon Supports

科学优点：已知许多电子、化学和物理性质取决于系统尺寸，特别是当长度尺度接近纳米或亚纳米尺寸时。这一发现在过去的几十年里推动了大量的科学和工程研究，特别是在电子材料、生物过程和催化方面。关于催化，人们认识到催化剂的活性不是其表面积的纯粹函数。事实上，随着催化剂尺寸的缩小，催化剂的行为不像大块金属，颗粒的形态和载体的性质等特征开始发挥重要作用。催化剂搜索的主要目标是识别具有特定化学活性的材料。然而，次要目标是催化剂在反应条件下保持其活性，这些反应条件可能包括高温、高或低pH值、与吸附剂的相互作用或电化学应用中电流的存在。由于催化剂中毒、烧结或催化剂或其支撑材料的溶解，恶劣的反应条件可能很快导致化学活性的丧失。为了保持活性，必须通过严格控制反应条件或改变催化剂/支撑材料的固有特性来减轻这些有害过程。因此，将进行计算研究，以了解如何操纵金属团簇和碳支撑材料之间的相互作用，以保持或增强催化剂的功能。这个项目是建立在催化剂烧结（部分）与催化剂与其支撑材料的相互作用有关的前提下的。有两个主要的机制，用于描述烧结过程：聚结和奥斯特瓦尔德成熟。由于这两个过程都涉及催化剂颗粒在载体上的扩散（无论是作为单个原子还是作为簇），因此通过降低催化剂的固有迁移率，应该显著提高催化剂的稳定性。换句话说，如果颗粒以某种方式固定或锚定在支架上，烧结应该会减少。这就是我们要探索的路线。重点将放在Pt， Pd, Ru， Rh和Au金属原子和团簇与（掺杂）碳载体的相互作用上。这些金属/载体组合可以在工业上广泛的催化和电化学应用中找到，包括燃料电池催化，脱碳反应，还原性胺化，酒精合成等。由于这些贵金属价格高昂（数量有限），在反应条件下长时间保持其原始活性尤为重要。这是催化的核心挑战之一。建模将主要使用电子结构计算来预测金属/支撑系统的各种物理和化学性质。特别是，将在原始和掺杂碳载体上进行Pt， Pd, Ru， Rh和Au催化剂颗粒的结构和活性表征。将研究各种掺杂方案，并将这些方案与典型的碳支持化学（羧基、羟基、Stone-Wales缺陷等）进行比较。与此同时，催化剂颗粒的烧结倾向，作为温度的函数和作为电场强度的函数（与电化学应用相关）将通过从头算MD模拟进行研究。最后，通过计算标准探针反应（如CO氧化）的反应机制，对金属颗粒的催化活性进行分析。更广泛的影响：教育和推广计划得到了高度重视，并制定了一项高影响战略，以传播科学成果。外展活动涉及K-12学生与阿拉巴马州伯明翰的麦克文科学中心合作，创建一个新的科学展览。此外，本科生将通过UA计算机荣誉课程参与该项目。最后，HBCU项目的教师将被纳入夏季研讨会，以及通过更传统的途径（研究生课程、会议演讲和期刊出版物）的其他受众。

0747690TurnerScientific Merit: Many electronic, chemical, and physical properties are known to depend upon system size, especially when the length scale approaches nanometer or sub-nanometer dimensions. This revelation has driven a significant amount of the scientific and engineering research over the past few decades, especially with regards to electronic materials, biological processes, and catalysis. With regards to catalysis, it is recognized that the activity of a catalyst is not a pure function of its surface area. In fact, as the size of the catalyst shrinks, the catalyst behaves less like a bulk metal, and characteristics such as the morphology of the particles and the nature of the support begin to play a significant role.The primary goal of a catalyst search is to identify materials with specific chemical activity. However, a secondary goal is for the catalyst to maintain its activity during reacting conditions, which may include high temperatures, high or low pH, interactions with adsorbates, or the presence of an electrical current in electrochemical applications. Harsh reacting conditions may quickly result in a loss of chemical activity, due to catalyst poisoning, sintering, or dissolution of the catalyst or its support material. In order to maintain activity, these detrimental processes must be mitigated, either by tightly controlling the reaction conditions or by altering the intrinsic properties of the catalyst/support material. As such, a computational investigation will be performed to understand how the interactions between metal clusters and carbon support materials might be manipulated in order to preserve or enhance catalyst function.This project is built upon the premise that catalyst sintering is (in part) related to the interaction of the catalyst with its support material. There are two primary mechanisms that are used to describe the sintering process: coalescence and Ostwald ripening. Since both processes involve the diffusion of the catalyst particles on the support (either as single atoms or as clusters), the catalyst stability should be significantly improved by reducing the inherent mobility of the catalysts. In other words, if the particles are somehow pinned or anchored to the support, sintering should decrease. This is the route that will be explored here. Attention will be focused on the interactions of Pt, Pd, Ru, Rh, and Au metal atoms and clusters with (doped) carbon supports. These metal/support combinations can be found in a wide range of catalytic and electrochemical applications in industry, including fuel cell catalysis, decarbonylation reactions, reductive amination, alcohol synthesis, etc. Due to the high price (and limited quantities) of these precious metals, it is particularly important to maintain their original activity under reacting conditions for extended periods of time. This is one of the central challenges of catalysis.The modeling will be primarily performed using electronic structure calculations to predict a variety of physical and chemical properties of the metal/support systems. In particular, characterization of the structure and activity of Pt, Pd, Ru, Rh, and Au catalyst particles on pristine and doped carbon supports will be performed. Various dopant schemes will be investigated, and these will be compared with typical carbon support chemistry (carboxyl groups, hydroxyl groups, Stone-Wales defects, etc.). Along with this, the propensity of the catalyst particles for sintering, as a function of temperature and as a function of electric field strength (pertinent to electrochemical applications) will be investigated with ab initio MD simulations. Finally, the metal particles will be analyzed with respect to their catalytic activity by calculating the reaction mechanisms of standard probe reactions, such as CO oxidation.Broader Impacts: The education and outreach plan has been given significant attention, and a high impact strategy has been developed for disseminating the science outcomes. The outreach activities involve K-12 students by partnering with the McWane Science Center in Birmingham, AL to create a new science exhibit. Also, undergraduate students will participate in this project through the UA Computer Based Honors Program. Finally, faculty at HBCU programs will be included in summer workshops, as well as other audiences through the more traditional avenues (graduate courses, conference presentations, and journal publications).