Multiscale Modeling of Bifunctional Catalysts for the Water-Gas-Shift Reaction

0932991 Heyden该奖项由2009年美国复苏和再投资法案（Public Law 111-5）资助。智力优势-对于具有一个以上关键表面中间体的非均相催化反应，多相催化剂可能比传统的单相催化剂具有显著优势，因为每个相都可以独立调节以激活关键反应步骤。同时，对双功能多相系统的理解相对较差。这是这个拟议的研究计划的目标，显着提高分子的理解在气相，可还原的氧化物表面，和贵金属簇的三相边界（TPB）的多相催化。为了在TPB进行化学反应的理论研究，PI和他的学生建议为这些系统开发和验证一种高效准确的计算策略。他们坚信，只有通过更精确的计算多尺度策略，才能可靠地研究强相关的可还原氧化物表面和金属簇上的反应，才有可能真正了解活性位点的性质，催化活性的起源以及反应条件下TPB的反应机理。作为计算研究的模型系统，他们打算研究二氧化钛和二氧化铈负载的Au、Pt和Pd的单簇和双簇上的水煤气变换（WGS）反应。他们的计算策略和对TPB活性位点性质的研究不限于WGS反应，但可能更普遍，因为已经表明可还原氧化物负载的贵金属对各种反应具有高活性，例如不饱和烃的选择性氢化和氧化。他们的计算策略涉及最先进的周期性平板计算，以建立和验证用于研究各种反应途径的周期性静电嵌入簇模型。与周期性板模型不同，周期性簇模型允许使用现代双杂化密度泛函，具有显着提高的准确性，用于模拟可还原氧化物表面和金属簇上的化学反应。在确定了相当准确的反应能和反应势垒后，他们打算根据仅从第一原理和绝对速率理论获得的数据开发微动力学反应器模型。借助微观动力学模型，他们将能够研究温度和气相化学势对反应机理和关键反应中间体的影响。此外，他们将能够通过分析电子结构如何随着贵金属簇和可还原氧化物的变化而改变，以及通过使用Nørskov的方法来区分电子效应与几何或结构效应，来确定活性位点活性的起源。最后，值得注意的是，该提案中概述的计算模型和方法以前没有用于多相催化的研究，并建议与南加州大学的Amiridis博士和Chen博士等实验学家合作，以验证和测试计算预测。更广泛的影响，科学-开发更精确的计算策略，用于研究气相TPB反应，可还原的氧化物表面和贵金属簇将显著增加这些令人惊讶的催化活性体系的理论研究的可靠性，这些催化活性体系在计算上非常难以描述。此外，了解这些系统独特催化活性的起源将可能有助于开发用于各种反应的改进催化剂，这些催化剂可以通过氧化物负载的贵金属选择性活化。教育-直接参与拟议研究的研究生和本科生将接触到一套全面的理论工具，使他们能够研究催化和材料科学此外，拟议研究的结果将被整合到研究生和本科生联合课程“多尺度建模：从电子到化学反应器”，目前正在由PI开发。社区外展-参与这项研究的研究生将在南加州大学的合作伙伴调查计划中度过一个秋季学期。她将协助从当地中学（82%的非洲裔美国人或西班牙裔血统）的科学教师整合工程和科学内容（包括她的研究）和解决问题的方法到科学课程。最后，PI参与了南加州大学的增强学习体验（ELE）计划，在该计划中，对化学工程感兴趣的高中生将获得一天的动手学习体验。

0932991 HeydenThis award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Intellectual Merit - For heterogeneously catalyzed reactions with more than one key surface intermediate, it is likely that multiphase catalysts have a significant advantage over conventional monophase catalysts since each phase can potentially be adjusted independently to activate a key reaction step. At the same time, understanding of bifunctional multiphase systems is relatively poor. It is the objective of this proposed research program to significantly enhance molecular understanding of heterogeneous catalysis at the three-phase boundary (TPB) of a gas-phase, a reducible oxide surface, and a noble metal cluster. To enable this theoretical investigation of chemical reactions at the TPB, the PI and his students propose to develop and validate a highly efficient and accurate computational strategy for these systems. It is their firm belief that only with a more accurate computational multiscale strategy that permits the reliable investigation of reactions on strongly correlated reducible oxide surfaces and metal clusters, will it be possible to truly understand the nature of the active sites, the origin of catalytic activity, and the reaction mechanism at the TPB under reaction conditions. As a model system for computational study, they intend to investigate the water-gas-shift (WGS) reaction on titania and ceria supported mono- and bimetallic clusters of Au, Pt, and Pd. Their computational strategy and study of the nature of the active site at the TPB is not limited to the WGS reaction but is likely more general as it has been shown that reducible oxide supported noble metals are highly active for various reactions such as the selective hydrogenation and oxidation of unsaturated hydrocarbons. Their computational strategy involves state-of-the-art periodic slab calculations to build and validate a periodic electrostatic embedded cluster model that is used for the study of various reaction pathways. Unlike periodic slab models, the periodic cluster model permits the use of modern doublehybrid density functionals with significantly improved accuracy for modeling chemical reactions on reducible oxide surfaces and metal clusters. Having determined reasonably accurate reaction energies and barriers, they intend to develop a microkinetic reactor model based on data obtained only from first principles and absolute rate theory. With the help of the microkinetic model, they will be able to study the effect of temperature and chemical potential of the gas phase on the reaction mechanism and key reaction intermediates. Furthermore, they will be able to determine the origin of the activity of the active sites by analyzing how the electronic structure is altered with changes in noble metal cluster and reducible oxide and by using Nørskov's method to distinguish electronic effects from geometric or structural effects. Finally, it is noted that the computational models and methods outlined in this proposal have not been used previously in the study of heterogeneous catalysis and collaboration with experimentalists such as Dr. Amiridis and Dr. Chen at USC is proposed to validate and test the computational predictions.Broader Impact, Science - The development of a more accurate computational strategy for studying reactions at the TPB of a gas-phase, a reducible oxide surface, and a noble metal cluster will significantly increase the reliability of theoretical investigations of these surprisingly catalytically active systems that are computationally very difficult to describe. Furthermore, understanding of the origin of the unique catalytic activity of these systems will likely aid the development of improved catalysts for various reactions that can be selectively activated by oxide supported noble metals.Broader Impact, Education - The graduate and undergraduate students directly involved in the proposed research will be exposed to a comprehensive set of theoretical tools that will allow them to study most issues in catalysis and material science. In addition, the results of the proposed research will be integrated in a joint graduate and undergraduate course "Multiscale Modeling: From Electrons to Chemical Reactors" that is currently being developed by the PI. Community Outreach - The graduate student involved in this research will spend one Fall semester in the Partners in Inquiry program at USC. She will assist a science teacher from a local middle school (82% African American or Hispanic origin) to integrate engineering and science content (including her research) and problem solving methods into the science curriculum. Finally, the PI is involved in the Enhanced Learning Experience (ELE) program at USC, in which high school students interested in chemical engineering are given a one day hands-on learning experience.