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将研究多元合金的选择性氢化催化反应性。由许多金属成分制成的催化剂，被称为“高熵合金”，可能为提高性能提供新的途径。然而，理解多金属相互作用是复杂的，因为当许多金属混合在一起时会形成大量的结构。这个合作研究团队将继续努力识别和量化催化剂中多达五种不同金属的复杂相互作用，使用一种结构明确的合金，称为金属间合金，以降低结构的复杂性。这些合金将包含三到五种不同的金属，允许团队通过系统地将更多的金属加入合金结构来探测这些复杂的金属相互作用。利用实验和计算相结合的方法，该团队旨在了解组成不同的金属间化合物对炔烃和烯烃选择性加氢的催化行为的起源。通过这个项目，dr。Rioux和Janik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，将有大量本科生参与研究，利用宾夕法尼亚州立大学已建立的招聘计划。γ-黄铜金属间结构的原子成分在四个对称不等价位上的分布是明确可控的。在固态合成过程中精确的化学计量控制可以制备M8-11Zn44-41体系，该体系将M （Pd, Ni）原子分布在所有Zn最近的邻居或小M3簇中。宾夕法尼亚州立大学的Rioux和Janik将制备、表征和检验通过替换一定数量的Pt、Ir、Cu和/或Au原子生成的三元、四元和五元γ-黄铜体系的反应性。控制成分复杂性的引入旨在通过结合多方面的实验和计算研究，使高熵材料的定量催化科学得以发展。H2-D2交换和乙烯加氢对三聚体活性位点的组成高度敏感，而1,3-丁二烯的选择性加氢将探测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对γ-黄铜金属间微观结构、晶体结构的严格表征以及对γ-黄铜HEIs上三聚体位点的表征方法来辅助。基于DFT-和团簇扩展计算的计算工作将定义稳定的体和表面三聚体组合作为γ-黄铜多元金属间成分的函数。基本反应能量的DFT计算将为微动力学模型提供比较速率的信息，假设分布一系列位点组成的表面上的速率将是由于Zn宿主中位点隔离而导致的单个位点速率的简单总和。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.