Collaborative Research: Predictive Modeling of Catalysis with Multiple Adsorbate Species

0731020/0730841施耐德，威廉F./沃尔弗顿，克里斯u。在现实条件下，非均相金属催化剂的表面覆盖着一层吸附物，这些吸附物彼此之间以及与催化剂表面的相互作用对催化功能有重大影响。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，因为即使在最简单的系统中也可能有大量的相互作用（例如最近邻，次近邻等）。在这个项目中，在合金理论界开发的用于处理批量有序问题的簇扩展（CE）技术被扩展到描述金属和双金属合金表面的吸附质相互作用。这些ce是根据精确的密度泛函理论（DFT）计算的少量吸附质排列的相对能量来参数化的。一旦参数化，它们为表面上任何原子排列的能量学提供了一个预测模型，这些信息被用于蒙特卡罗模拟，以预测首选吸附几何形状、表面有序、表面相图和吸附热力学。同样的方法也同样用于捕获局部吸附质顺序对表面反应活化能的影响。这种表面DFT-CE方法的少数现存例子仅限于单一吸附。该项目从两个方面扩展了该方法，这对其在多相催化中的广泛应用至关重要：一是三元表面，它可以捕获表面上多种吸附物的行为；二是ce，它可以捕获双金属催化剂表面组成与反应物吸附之间的耦合。这些工具应用于Pt和Au金属表面的O2活化和催化氧化问题，这些问题与从低温燃料电池到环境催化的问题相关。ce被构建并用于预测解离氧吸附的热力学（通过平衡蒙特卡罗）和动力学（通过动力学蒙特卡罗），以及氧与NO还原剂的反应作为外部反应物条件（T, PO2…）的函数。为了评估合金化调节催化活性的潜力，还构建了ce，并用于描述Pt-Au和Pt-Ag合金在许多相互作用情景下的平衡表面组成和氧反应性。这项工作探讨了DFT-CE方法在描述表面反应性方面的局限性，并为更近似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，并建立在两个PIs在表面反应性（Schneider, Notre Dame）和合金理论（Wolverton, Northwestern）方面的互补专业知识的基础上。通过高度协作的努力将这两个社区连接起来，这项工作为多相催化带来了新的理解、新的能力和意想不到的创新的强大潜力。结果在催化和材料科学界的广泛传播进一步促进了思想的交流。此外，我们感兴趣的具体问题——o2的催化活化——对社会具有最根本和最实际的重要性。该计划为几位化学工程和材料科学研究生提供了一个独特的培训环境，用于应用模拟和跨学科研究，这得益于合作机构的密切关系。pi通过让代表性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。这项工作还支持了常规和夏季短期课程的发展，以模拟实践和应用于两组。总之，这个项目综合了教育和培训，在一个协作的，跨学科的，多机构的研究项目中开发新的模拟工具和建模方法，在多相催化的局部问题的背景下。

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.