Collaborative Research: Predictive Modeling of Catalysis with Multiple Adsorbate Species

0731020/0730841施耐德，威廉·F/伍尔弗顿，克里斯托大学。圣母大学/西北大学在现实世界条件下，多相金属催化剂的表面覆盖着吸附物质，这些吸附物质相互作用和集体与催化剂表面的相互作用可能会对催化功能产生重大影响。金属表面反应的原子级模拟通常只能以近似的方式解释这些相互作用，因为数量很大(例如，最近邻、次最近邻等)。即使在最简单的系统中也是可能的。在这个项目中，团簇展开(CE)技术被扩展到描述金属和双金属合金表面的吸附相互作用。根据密度泛函理论(DFT)对少量吸附排布的相对能量的精确计算，对这些CE进行了参数化。一旦被参数化，它们就为表面原子的任何排列提供了一个预测模型--蒙特卡罗模拟中使用的信息来预测首选的吸附几何结构、表面有序、表面相图和吸附热力学。同样的方法也被用来捕捉局部吸附顺序对表面反应活化能的影响。现有的这种表面DFT-CE方法的少数例子仅限于单一的吸附物。该项目将该方法扩展到两个方面，这是它们在多相催化中更广泛应用的关键：三元表面，它可以捕捉到表面上多个吸附物的行为，以及CE，它捕捉到双金属催化剂的表面组成和反应物吸附之间的耦合。这些工具被应用于铂和金金属表面的氧气活化和催化氧化问题--从低温燃料电池到环境催化等相关问题。通过平衡蒙特卡罗模拟和动力学蒙特卡罗模拟，预测了氧的离解吸附和氧与NO还原剂反应的热力学(通过平衡蒙特卡罗)和动力学(通过动力学蒙特卡罗)。为了评估通过合金化来调节催化活性的可能性，还构建了CES，并用它来描述在许多相互作用场景中铂-金和铂-银合金的平衡表面组成和氧反应活性。这项工作探索了DFT-CE方法在描述表面反应性方面的局限性，并为更接近的处理提供了高质量的基准。这里所做的工作跨越了学科界限，围绕着两个PI在表面反应性(施耐德，巴黎圣母院)和合金理论(沃尔弗顿，西北)方面的互补专业知识而建立。通过在高度协作的努力中将这两个社区联系起来，这项工作带来了新的理解、新的能力和在多相催化领域进行意想不到的创新的强大潜力。向催化和材料科学界广泛传播成果进一步促进了思想的交流。此外，人们感兴趣的具体问题--O2的催化活化--对社会具有最基本和实际的重要性。该计划为几个化学工程和材料科学研究生提供了一个独特的培训环境，在合作机构的密切联系下，促进了应用模拟和跨学科研究。私人投资机构通过让代表不足的群体参与研究和让本科生参与研究来维持和促进多样化的研究环境。这项工作还支持在两个小组中开发模拟实践和应用方面的常规课程和暑期短期课程。总而言之，这一计划综合了教育和培训在一个协作的，跨学科的，多机构的研究计划，开发新的模拟工具和建模方法在多相催化的主题问题的背景下。

0731020/0730841Schneider, William F./Wolverton, ChrisU. Notre Dame/Northwestern UniversityUnder real world conditions the surface of a heterogeneous metal catalyst is covered with adsorbates, and the interactions of these adsorbates with each other and collectively with the catalyst surface can have a major impact on catalytic function. Atomic-level simulations of reactions at metal surfaces often can account for these interactions in only approximate ways, because of the large number (e.g. nearest-neighbor, next-nearest-neighbor, etc.) possible in even the simplest system. In this project, cluster expansion (CE) techniques developed in the alloy theory community to treat bulk ordering problems are extended to the description of adsorbate interactions at metal and bimetallic alloy surfaces. These CEs are parameterized against accurate density functional theory (DFT) calculations of the relative energies of a small number of adsorbate arrangements. Once parameterized, they provide a predictive model for the energetics of any arrangement of atoms at the surface-information that is used in Monte Carlo simulations to predict preferred adsorption geometries, surface orderings, surface phase diagrams, and adsorption thermodynamics. This same approach is similarly used to capture the effects of local adsorbate order on the activation energies of surface reactions. The few extant examples of this surface DFT-CE approach are limited to single adsorbates. This project extends the approach in two ways key to their wider application in heterogeneous catalysis: to ternary" surfaces, which can capture the behavior of multiple adsorbates at a surface, and to CEs that capture the coupling between the surface composition of a bimetallic catalyst and adsorption of reactants. These tools are applied to the problem of O2 activation and catalytic oxidation at Pt and Au metal surfaces-relevant to problems from low-temperature fuel cells to environmental catalysis. CEs are constructed and used to predict the thermodynamics (through equilibrium Monte Carlo) and kinetics (through kinetic Monte Carlo) of dissociative oxygen adsorption and to the reaction of oxygen with an NO reductant as a function of external reactant conditions (T, PO2 ...). To evaluate the potential for tuning catalytic activity by alloying, CEs are also constructed and used to describe the equilibrium surface composition and oxygen reactivity of Pt-Au and Pt-Ag alloys in a number of interaction scenarios. This work probes the limits of the DFT-CE methodology for describing surface reactivity and provides high-quality benchmarks for more approximate treatments. The work done here crosses disciplinary boundaries and is built around the complementary expertise of the two PIs in surface reactivity (Schneider, Notre Dame) and alloy theory (Wolverton, Northwestern). By bridging these two communities in a highly collaborative effort, this work brings new understanding, new capabilities, and a strong potential for unanticipated innovation in heterogeneous catalysis. Broad dissemination of results to the catalysis and materials science communities further promotes cross-fertilization of ideas. In addition, the specific problem of interest-the catalytic activation of O2-is of utmost fundamental and practical importance to society. The program provides a unique training environment for several chemical engineering and materials science graduate students in applied simulation and interdisciplinary research, facilitated by the close proximity of the partner institutions. The PIs both maintain and promote diverse research environments by involving underrepresented groups and engaging undergraduates in research. The work also supports the development of regular and summer short course curricula in simulation practice and application in both groups. In summary, this program synthesizes education and training within a collaborative, interdisciplinary, multi-institutional research program developing new simulation tools and modeling approaches in the context of topical problems in heterogeneous catalysis.