Collaborative Research: Structure, Dynamics, and Catalysis with Dilute Bimetallic and Single Atom Alloy Nanoparticles

在化学系化学催化项目的支持下，David Flaherty（佐治亚理工学院）、David hibitts（佛罗里达大学）和Ayman Karim（弗吉尼亚理工学院）将研究双金属纳米颗粒与氧反应的结构、动力学和催化作用之间的联系。该团队将创建、表征、模拟和测试不同金属的原子如何在主要由金和少量（1-5%）的第二元素（如钯或铂）组成的纳米颗粒表面上移动和促进反应。这些材料通常被称为单原子合金（SAA）催化剂。这些材料为国内生产能源载体和平台化学品（例如生物质、页岩气的增值、燃料电池和电解槽的操作）提供了高速率和高选择性的许多反应。SAA目前面临着每克贵金属所使用的活性位点数量低得令人沮丧的问题。该合作团队的目标是开发制造直径更小（2纳米）的SAA纳米颗粒的方法来解决这个问题，然后测试这些SAA的新兴和有益的催化性能是否随着纳米颗粒尺寸的减小而保持不变。在这里，该团队将结合量子化学模拟和多尺度建模的尖端方法，使用同步加速器方法对操作催化剂进行表征，以及催化剂测试和光谱学，以了解纳米颗粒如何在与催化相关的不同反应气体（例如氧气，氢气，一氧化碳）的组合中重组。随后，研究小组将评估一个试验台反应（用氢还原氧）的速率和选择性如何取决于纳米颗粒表面原子的空间组织。将开发的方法将对其他动态催化剂系统有用，并将纳入研究生水平的课程。拟议的工作包括以实验室为基础的研究生和本科生教育，并重点努力增加妇女在催化科学中的参与，特别是通过NSF REU（本科生研究经验）机会和三个合作机构的研究人员交叉培训。根据该奖项，Flaherty/Hibbitts/Karim合作团队的目标是了解双金属和SAA材料的结构、动力学和催化性能如何取决于平均粒径、组成和支持特性，以及所有影响表面原子的配位饱和度及其最近和次近邻原子的特性的因素。该团队将结合精确的合成、先进的表征技术（包括原位、operando x射线吸收光谱、微热法、红外光谱）和计算方法（利用密度泛函数理论和动力学蒙特卡罗模拟全纳米粒子）来解决SAA催化剂的复杂性和动力学问题。测试反应系统的速率和选择性被证明对这些材料（H2 + O2→H2O2）具有结构敏感性，将用于探测活性催化剂的表面结构，这是一个挑战，因为高压和复杂的溶剂通常使表征变得困难。首先，制备平均直径为1-2、~6和~10 nm的富金双金属合金纳米颗粒（即M1Aux材料，其中M = Pd、Pt、Rh），表征其合成后的结构，然后在较长时间内研究吸附和反应对其结构的影响。其次，确定吸附能、活性位基序和纳米颗粒结构之间的热力学关系。第三，将研究元素同一性、摩尔分数、活性金属配位与反应速率、选择性和形成H2O2和H2O的障碍之间的基本联系。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, David Flaherty (Georgia Institute of Technology), David HIbbitts (University of Florida), and Ayman Karim (Virginia Polytechnical Institute) will examine the connections among the structure, dynamics, and catalysis of reactions with oxygen on bimetallic nanoparticles. The team will create, characterize, simulate, and test how atoms of distinct metals move and facilitate reactions upon the surfaces of nanoparticles comprised primarily of gold with small amounts (1-5%) of a second element such as palladium or platinum. These materials are commonly described as single atom alloy (SAA) catalysts. These materials offer high rates and selectivities for numerous reactions important for domestic production of energy carriers and platform chemicals (e.g., valorization of biomass, shale gas, operation of fuel cells and electrolyzers). SAA currently suffer from a distressingly low number of active sites per gram of precious metal used. The collaborative team aims to develop methods to create SAA nanoparticles with smaller diameters ( 2 nm) to remedy this problem, and then test if the emergent and beneficial catalytic properties of these SAA are preserved as the size of the nanoparticles decreases. Here, the team will combine cutting-edge methods in quantum chemical simulations and multiscale modeling, characterization of operating catalysts using synchrotron methods, and catalyst testing and spectroscopy to learn how the nanoparticles restructure in different combinations of reactive gases relevant for catalysis (e.g., oxygen, hydrogen, carbon monoxide). Subsequently, the team will assess how rates and selectivities for a testbed reaction (reduction of oxygen with hydrogen) depend on the spatial organization of the atoms on the nanoparticle surface. Methods that will be developed will be useful for other dynamic catalyst systems and will be integrated into graduate-level courses. The proposed work involves lab-based education of graduate and undergraduate students and focused efforts to increase participation of women in catalysis science, especially with NSF REU (Research Experiences for Undergraduates) opportunities and cross-training of researchers across the three partnering institutions.Under this award, the collaborative Flaherty/Hibbitts/Karim team aims to learn how the structure, dynamics, and catalytic properties of bimetallic and SAA materials depend upon mean particle diameters, composition, and support identity, all factors that impact the coordinative saturation of surface atoms and the identity of their nearest and next-nearest neighbor atoms. The team will couple precise synthesis, advanced characterization techniques (including n situ, operando X-ray absorption spectroscopy, microcalorimetry, infrared spectroscopy), and computational methods (simulations of full nanoparticles with density functional theory and kinetic Monte Carlo) to address the complexity and dynamics of SAA catalysts. A testbed reaction system with rates and selectivities proven to be structure-sensitive with respect to these materials (H2 + O2 → H2O2) will be used to probe the surface structures of active catalysts, a challenge as the high pressures and complex solvents used often render characterization difficult. First, Au-rich bimetallic alloy nanoparticles (i.e., M1Aux materials, where M = Pd, Pt, Rh) with mean diameters of 1-2, ~6 and ~10 nm will be created, their post-synthesis structures will be characterized, and then the influence of adsorption and reactions on their structures will be examined over extended periods. Second, the thermodynamic relationships among adsorption energies, active site motifs, and nanoparticle structure will be determined. Third, the fundamental connections surrounding elemental identity, mole fraction, and coordination of the reactive metal and reaction rates, selectivities and barriers for H2O2 and H2O formation will be examined.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.