Surface Composition and Chemical Behavior of Supported Single-Atom Alloy (SAA) Nanoparticles under Catalytic Conditions

在化学系化学催化项目的支持下，滨江加州大学的弗朗西斯科扎埃拉教授正在研究所谓的单原子合金（SAA）催化剂的化学行为。 催化在工业中广泛用于制造化学品，并且过渡金属在许多情况下是所使用的催化剂的关键组分。 为了调节金属催化剂的性质以优化催化性能，有时使用两种或更多种金属的合金。 近年来，人们对使用特定版本的金属合金SAA作为催化剂产生了很大的兴趣，其中少量的一种金属，例如Zaera实验室中的铂（Pt），分散在第二种（Cu）的纳米颗粒（NP）上以添加特定的新功能。 在碳氢化合物氢化的情况下，一系列重要的催化过程，其中氢原子（H）被添加到碳-碳或碳-氧多重键上，使用模型系统的研究表明，需要Pt原子来解离H2以提供所需的H原子。 然而，在实际催化条件下的初步研究表明，单个原子的行为可能更加微妙。 该项目的重点是表征催化条件下SAA催化剂表面的性质，以更好地了解少数（Pt）和多数（Cu）金属的行为及其对加氢催化的贡献，以提高催化性能。 从这项工作中获得的知识旨在帮助调整精细化学品工业生产过程的选择性。从这项工作中获得的知识也将有助于教育目的，通过提供数据来说明动力学，催化和NP合成的基本原理，在本科生和研究生班。与拉丁美洲研究团体的合作正在形成，学生参与研究的人数不足的团体也在努力。在这些研究中，滨江的加州大学的弗朗西斯科扎埃拉教授正在研究催化条件下负载型SAA纳米颗粒（NPs）的表面组成和化学行为。 该项目的主要目标是在原位或操作条件下（在进行催化过程时）表征SAA催化剂，以弥合压力和材料差距，并更好地了解其工作表面化学。 两个假设支持这一提议：（1）少数金属（Pt）可能在反应条件下扩散到本体中，并以远程方式影响催化（压力间隙的直接后果）;以及（2）这种环境诱导的金属扩散可能在不同条件下发生在负载型NP中与本体材料中（材料间隙的直接表现）。 三个平行的实验方法被遵循，以测试的关键假设。 首先，催化条件下的动力学测量正在进行模型系统，通过使用所谓的“高压电池”和补充和相关的结果，从原位表征的表面使用反射吸收红外光谱（RAIRS）。 第二，正在开发合成方法以制造充分混合的稀释合金和核-壳型纳米颗粒，以研究反应条件下金属的可能扩散和混合。第三，催化剂在催化条件下原位和在操作条件下通过X射线吸收光谱（XAS）来表征，以评估少数原子周围配位层的变化，这是确定它们在表面与本体内部的存在的一种方法，并且通过红外吸收光谱（IR）来表征，以提取关于反应物的吸附模式的信息并滴定在催化条件下在表面处可用的少数原子。 该提案将研究与模型系统、新的催化剂合成方法、催化剂的原位光谱研究和量子力学计算相结合，以回答一个关键问题;即压力和材料间隙对SAA性能的影响，宽-该奖项反映了NSF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。

With the support of the Chemical Catalysis program in the Division of Chemistry, Professor Francisco Zaera of the University of California, Riverside is studying the chemical behavior of so-called single atom alloy (SAA) catalysts. Catalysis is used extensively in industry to manufacture chemicals, and transition metals are in many instances the key components of the catalysts used. To tune the properties of metal catalysts to optimize catalytic performance, alloys of two or more metals are sometimes used. In recent years, much interest has developed in using a particular version of metal alloys, SAAs, as catalysts where a small amount of one metal, e.g. platinum (Pt) in the Zaera lab, is dispersed on nanoparticles (NPs) of a second (Cu) to add specific new functionality. In the case of hydrocarbon hydrogenations, a family of important catalytic processes where hydrogen atoms (H) are added to carbon-carbon or carbon-oxygen multiple bonds, research using model systems has suggested that the Pt atoms are needed to dissociate H2 to provide the required H atoms. However, preliminary studies under realistic catalytic conditions have indicated that the behavior of the single atoms may be more nuanced. This project focuses on characterizing the nature of the surfaces of SAA catalysts under catalytic conditions to better understand the behavior of the minority (Pt) and majority (Cu) metals and their contributions to hydrogenation catalysis to improve catalytic performance. The knowledge derived from this work is aimed to help tune the selectivity of processes for the industrial production of fine chemicals. The knowledge derivied from this work will also be useful for educational purposes, by providing data to illustrate basic principles in kinetics, catalysis, and NP synthesis in undergraduate and graduate classes. Collaborations with Latin American research groups are being forged, and student participation from groups underrepresented in research is being pursued.In these studies, Professor Francisco Zaera of the University of California, Riverside is studying the surface composition and chemical behavior of supported SAA nanoparticles (NPs) under catalytic conditions. The main objective of this project is to characterize SAA catalysts in situ or under operando conditions (while carrying out catalytic processes) to bridge the pressure and materials gaps and better understand their working surface chemistry. Two hypotheses underpin this proposal: (1) that the minority metal (Pt) may diffuse into the bulk under reaction conditions and influence catalysis in a remote way (a direct consequence of the pressure gap); and (2) that such environment-induced metal diffusion may occur under different conditions in supported NPs vs. in bulk materials (a direct manifestation of the materials gap). Three parallel experimental approaches are being followed to test the key hypotheses. First, kinetic measurements under catalytic conditions are being performed on model systems by using a so-called "high-pressure cell" and complemented and correlated with results from in situ characterization of the surface using reflection-absorption infrared spectroscopy (RAIRS). Second, synthetic methods are being developed to make well mixed diluted alloys and core-shell bimetallic NPs to investigate the possible diffusion and intermixing of the metals under reaction conditions. Third, catalysts are being characterized under catalytic conditions in situ and under operando conditions by X-ray absorption spectroscopy (XAS) to evaluate changes in the coordination sphere around the minority atoms, one way to determine their presence on the surface vs. inside the bulk, and by infrared absorption spectroscopy (IR), to extract information about the adsorption mode of the reactants and to titrate the minority atoms available at the surface under catalytic conditions. The proposal combines studies with model systems, new catalyst synthesis methodology, in situ spectroscopic studies of catalysts, and quantum mechanics calculations to answer a critical question; namely, the effect of the pressure and materials gaps on SAA performance, with wide-ranging implications to the field of catalysis.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.