Taming the Complexity of High Entropy Alloy for Catalysis using Multinary Intermetallics

在化学系化学催化项目的支持下，宾夕法尼亚州立大学的Robert Rioux和Michael Janik将研究多元合金用于选择性氢化催化的反应性。 用许多金属成分制成的催化剂，称为“高熵合金”，可以提供改进性能的新途径。然而，理解多金属相互作用是复杂的，因为当将许多金属混合在一起时会形成大量的结构。 该合作研究团队将努力识别和量化催化剂中与多达五种不同金属的复杂相互作用，使用结构定义的合金，称为金属间化合物，以降低结构复杂性。 这些合金将包含三到五种不同的金属，使团队能够通过系统地将更多的金属引入合金结构来探测这些复杂的金属相互作用。 使用实验和计算相结合的方法，该团队的目标是了解组成多样的金属间化合物对炔和烯烃选择性氢化的催化行为的起源。 通过这个项目，Rioux和Janik博士将帮助培养下一代催化科学家，以解决化学催化剂设计和优化中的基础和应用问题。 作为该项目的一部分，将有大量的本科生参与研究，利用宾夕法尼亚州立大学的既定招聘计划。γ-黄铜金属间化合物结构在四个对称性不相等的位置中提供了其原子成分的明确和可控的分布。 在固态合成过程中精确的化学计量控制使得能够制备M8- 11 Zn 44 -41系统，该系统分布由所有Zn最近邻隔离或在小的M3簇中的M（Pd，Ni）原子。宾夕法尼亚州立大学的Rioux和Janik将制备、表征和检查通过取代一定数量的Pt、Ir、Cu和/或Au原子产生的三元、四元和五元γ-黄铜系统的反应性。 控制引入组成的复杂性，旨在使高熵材料的定量催化科学的发展，通过一个综合的，多方面的实验和计算研究。 H2-D2交换和乙烯氢化对三聚体位点的组成高度敏感，而1，3-丁二烯的选择性氢化将探测对三聚体活性位点组成的选择性。 对观察到的催化活性-选择性的解释将通过γ-黄铜金属间微结构、晶体结构的严格表征以及表征γ-黄铜HEI上存在的三聚体位点的方法来辅助。 基于DFT和团簇展开计算的计算工作将定义作为多元γ-黄铜金属间化合物组成的函数的稳定的本体和表面三聚体组装体。 DFT计算的基本反应能量将通知微动力学模型比较率，与假设，表面上的利率分布的网站组合物的阵列将是一个简单的总和，个别网站的利率由于网站隔离在Zn host.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

With support from the Chemical Catalysis program in the Division of Chemistry, Robert Rioux and Michael Janik of the Pennsylvania State University will examine the reactivity of multinary alloys for selective hydrogenation catalysis. Catalysts made with many metal constituents, referred to as “high entropy alloys,” may offer new avenues for improved performance. However, understanding the multi-metal interactions is complex due to the large number of structures that form when mixing many metals together. This collaborative research team will pursue an effort to identify and quantify these complex interactions in catalysts with up to five different metals using a structurally defined alloy, called an intermetallic, to reduce the structural complexity. These alloys will contain from three to five different metals allowing the team to probe these complex metal interactions by systematically incorporating more metals into the alloy structure. Using a combined experimental and computational approach, the team aims to understand the origin(s) of the catalytic behavior of compositionally-diverse intermetallics for selective hydrogenation of alkynes and alkenes. Through this project, Drs. Rioux and Janik will help to train the next generation of catalytic scientists to solve fundamental and applied problems in chemical catalyst design and optimization. There will a significant participation of undergraduates in research as part of this projecting, leveraging established recruitment programs at Pennsylvania State University.The γ-brass intermetallic structure offers well-defined and controllable distribution of its atomic constituents among four symmetry inequivalent sites. Precise stoichiometric control during solid-state synthesis enables preparation of M8-11Zn44-41 systems that distribute M (Pd, Ni) atoms either isolated by all Zn nearest neighbors or in small M3 clusters. Rioux and Janik of the Pennsylvania State University will prepare, characterize, and examine the reactivity of ternary, quaternary, and quinary γ-brass systems generated by substituting some number of Pt, Ir, Cu, and/or Au atoms. Controlled introduction of compositional complexity is designed to enable the development of a quantitative catalysis science of high entropy materials through a combined, multi-faceted experimental and computational study. H2-D2 exchange and ethylene hydrogenation are highly sensitive to the composition of the trimer sites, while selective hydrogenation of 1,3-butadiene will probe selectivity on the trimer active site composition. Interpretation of the observed catalytic activity-selectivity will be aided by rigorous characterization of γ-brass intermetallic microstructure, crystal structure, and methods to characterize the trimer sites present on γ-brass HEIs. Computational efforts based on DFT- and cluster-expansion calculations will define stable bulk and surface trimer assemblies as a function of multinary γ-brass intermetallic composition. DFT calculations of elementary reaction energetics will inform microkinetic models to compare rates, with the hypothesis that rates on surfaces distributing an array of site compositions will be a simple sum of rates on individual sites due to site isolation in the Zn host.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.