Unconventional Noble Metal Nanoparticles with Enhanced Catalytic Properties: A Combined Experimental and Theoretical Study

在化学系大分子、超分子和纳米化学项目的支持下，该项目的目标是制备用于能源和环境应用的新型金属纳米颗粒催化剂。许多大规模催化过程负责燃料、聚合物和纺织品、药物和食品添加剂的形成，并用于毒素和环境污染物的修复，其中许多需要贵金属催化剂。贵金属既稀缺又昂贵。因此，找到制备需要较少贵金属的催化剂的方法，同时保持催化性能并减少形成的废物副产物的数量，是至关重要的。金属纳米颗粒是由几百到几千个原子组成的离散实体。它们可能看起来是小碎片，或者是从大块金属上“切下来”的碎片。然而，已知它们具有优于大块金属的特性，包括增强的催化行为。对于发生在金属表面的重要化学反应，贵金属纳米颗粒非常有吸引力，因为它们的表面积与其体积相比非常大，从而提高了效率。在这个项目中，德克萨斯大学奥斯汀分校的西蒙·汉弗莱博士和格雷姆·亨克尔曼博士的研究小组正在结合他们的专业知识，制备具有以前未研究过的结构的贵金属纳米颗粒，并解释这种结构是如何提高催化性能的。这项研究活动的一个主要目标是制备基于金属（合金）混合物的纳米粒子，这种金属可以用更便宜、更容易获得的金属来稀释非常昂贵的金属，同时也可以提高催化性能。另一个目标是使用微波加热作为一种更便宜、更快速的制备纳米颗粒的方法。该项目还包含了重要的教育目标，旨在激励本科生积极参与研究的各个方面。德克萨斯大学奥斯汀分校正在引入一个新的微波材料合成新生研究计划（FRI）流，使本科生能够从事基于实验室的研究，并促进对科学研究的更深层次的欣赏。这是德克萨斯大学奥斯汀分校材料合成和催化小组（Simon Humphrey）和理论建模小组（Graeme Henkelman）之间的合作项目。本研究活动的主要目标是合成具有特定成分的金属纳米颗粒（MNPs），在与工业相关的大规模化学转化相关的模型催化反应中测试MNPs，并使用详细和最先进的理论方法来深入了解表面反应性与MNP结构之间的关系。实验和理论相结合，阐明了反应性作为组成的直接函数的一般趋势；这最终提供了重要的信息，可以应用于指导合成其他具有期望反应性的新MNPs。该项目的特点是利用创新和技术相关的微波辅助方法制备各种新型金属纳米颗粒（MNPs）。与经典方法相比，微波辅助合成允许更快的反应时间，更容易扩大规模，并且还可以获得其他方法无法获得的产品。微波加热技术在有机化学和生物科学领域日益普及，但在材料和无机化学领域尚未得到充分利用。在这个项目中，微波合成被用来获得具有确定尺寸和表面结构的MNPs，以及不寻常的杂化核壳和合金成分。这些以前未研究过的MNPs的表面化学通过模型反应研究进行了探索，包括蒸汽和液相反应，包括碳氢化合物氢化，羰基化和NOx还原。该项目的另一个目标是发展新的理论方法，可以提供比目前可用的更准确的表面反应性描述。该项目还包含了重要的教育目标，旨在激励本科生积极参与研究的各个方面。德克萨斯大学奥斯汀分校正在引入一个新的微波材料合成新生研究计划（FRI）流，使本科生能够从事基于实验室的研究，并促进对科学研究的更深层次的欣赏。

With support from the Macromolecular, Supramolecular and Nanochemistry program in the Division of Chemistry, the goal of this project is to prepare new metal nanoparticle catalysts for energy and environmental applications. Many large-scale catalytic processes are responsible for the formation of fuels, polymers and textiles, drugs and food additives, and are used in the remediation of toxins and environmental pollutants, and many of these require precious metal catalysts. Precious metals are both scarce and expensive. It is, therefore, of critical importance to find ways to prepare catalysts that require less precious metal, whilst maintaining the catalytic performance and also reducing the amount of waste by-products that are formed. Metal nanoparticles are discrete entities consisting of just a few hundred to a few thousand atoms. They might appear to be small fragments or as pieces "cut-away" from bulk metals. However, they are known to have properties that are superior to bulk metal, including enhanced catalytic behavior. For important chemical reactions that occur on metal surfaces, precious metal nanoparticles are very attractive because they have very large surface areas compared to their volumes, resulting in improved efficiency. In this project, the research groups of Dr. Simon Humphrey and Dr. Graeme Henkelman at the University of Texas at Austin are combining their expertise to prepare precious metal nanoparticles with previously unstudied structures, and to explain how the structures result in improved catalytic properties. A major goal of this research activity is to prepare nanoparticles based on mixtures of metals (alloys) that permits the dilution of very expensive metals with cheaper and more available metals, while also achieving improved catalytic properties. Another goal is to use microwave heating as a cheaper and faster way to prepare the nanoparticles. This project also incorporates important educational goals that are aimed at inspiring undergraduate students to actively participate in aspects of the research. A new microwave materials synthesis Freshman Research Initiative (FRI) stream is being introduced at the University of Texas - Austin, which enables undergraduates to engage in laboratory-based research, and promotes a deeper appreciation for scientific research. This is a collaborative project between a materials synthesis and catalysis group (Simon Humphrey) and a theoretical modeling group (Graeme Henkelman) at the University of Texas at Austin. The major objectives of this research activity are to synthesize metal nanoparticles (MNPs) with defined compositions, to test the MNPs in model catalytic reactions relating to industrially-relevant large-scale chemical transformations, and to use detailed and state-of-the-art theoretical approaches to gain a deep understanding of the relationships between surface reactivity and MNP structure. Experiment and theory are combined to elucidate general trends in reactivity as a direct function of composition; this ultimately provides important information that can be applied to direct the synthesis of other new MNPs with desired reactivity. The project features the preparation of a variety of novel metal nanoparticles (MNPs) using an innovative and technologically-relevant microwave-assisted method. Compared to classical methods, microwave-assisted synthesis allows for faster reaction times, easier scale-up, and can also allow access to products that cannot otherwise be obtained. Microwave heating is becoming popular in organic chemistry and the biosciences, but it has still yet to be fully exploited in materials and inorganic chemistry. In this project, microwave synthesis is exploited to gain access to MNPs with defined size and surface structure, and with unusual hybrid core-shell and alloy compositions. The surface chemistry of these previously unstudied MNPs are explored through model reaction studies including vapor- and liquid-phase reactions including hydrocarbon hydrogenation, carbonylation, and NOx reduction. Another goal of this project is the development of new theoretical approaches that can provide a more accurate description of surface reactivity than is presently available. This project also incorporates important educational goals that are aimed at inspiring undergraduate students to actively participate in aspects of the research. A new microwave materials synthesis Freshman Research Initiative (FRI) stream is being introduced at the University of Texas - Austin, which enables undergraduates to engage in laboratory-based research, and promotes a deeper appreciation for scientific research.