Model Nanocluster Catalysts: The Role of Size, Shape and Composition on the Catalytic Activity of Small Metal Oxide and Bimetallic Clusters on Oxide Surfaces

化学催化计划支持加州大学圣巴巴拉分校(UCSB)的Steven Buratto、Michael Bowers和Horia Metiu教授制备、表征和测试两种新型纳米结构催化剂，它们的共同特征是非常小、孤立、定义明确的催化活性中心。研究人员设计和建造了一种独特的、高度通用的设备，可以通过将气相中质量选择的纳米团簇沉积到单晶氧化物载体上来生产模型催化剂(包括金属和金属氧化物)。利用常规的表面科学方法和超高真空与扫描探针显微镜(UHV-STM)相结合的方法对这些纳米团簇催化剂进行了表征，考察了反应前后纳米团簇的大小和形状。在超高压下使用程序升温脱附(TPD)和程序升温反应(TPR)监测这种模型催化剂的化学，并使用连接到表面科学室的高压间歇反应器在高压下监测这种模型催化剂的化学。具体地说，研究人员将制备并研究负载在单晶二氧化钛(110)表面的非常小的VxOy质量选择簇合物在甲醇氧化脱氢为甲醛中的催化活性。他们将探索催化活性与x和y的函数关系，以建立反应机理的模型。他们还将制备和研究负载在单晶二氧化钛(110)表面上的各种组成的极小质量选择的二元簇合物(如钯/金和铂/锡合金)在合成乙酸乙烯酯和烯烃选择加氢中的催化活性随组成的变化，并开发反应机理的模型。大量工业过程使用负载在氧化物表面的纳米团簇(金属和金属氧化物)来执行不会发生的反应，或者如果在块状材料上进行将不会在商业上成功进行的反应。在这笔拨款支持的研究中，研究人员将利用最先进的实验和理论方法，非常详细地探索定义明确的纳米簇催化剂的催化活性，并在原子水平上发展对催化化学的基本理解。通过这项研究开发的概念将有助于优化使用这些纳米级催化剂的重要工业过程，并为发现新的纳米级催化材料提供有价值的见解。这笔赠款支持的研究人员还将积极接触圣巴巴拉地区的K-12学校。他们计划开发一个关于多相催化原子论观点的教程演示文稿，该演示文稿将被包括在UCSB目前活跃的部门推广计划中。此外，参与该项目的研究人员将每年访问圣巴巴拉县和文图拉县的高中三次，讨论他们的研究及其影响，并促进科学教育。

The Chemical Catalysis Program supports Professors Steven Buratto, Michael Bowers, and Horia Metiu from the University of California at Santa Barbara (UCSB) to prepare, characterize, and test two new types of nanostructured catalysts, having the common feature of being very small, isolated, well-defined catalytically-active sites. The investigators have designed and constructed a unique, highly versatile apparatus which allows production of model catalysts (both metals and metal oxides) by deposition of mass-selected nanoclusters from the gas phase onto single crystal oxide supports. These well-defined nanocluster catalysts are characterized using a normal array of surface science methods and, in addition, utilization of ultrahigh vacuum combined with scanning-tip microscopy (UHV-STM) methods to probe the size and shape of the nanoclusters before and after reaction. The chemistry of such model catalysts is monitored in UHV using temperature-programmed desorption (TPD) and temperature-programmed reaction (TPR) and at elevated pressures using a high pressure batch reactor attached to the surface science chamber. Specifically, the investigators will prepare and study the catalytic activity of very small VxOy mass-selected clusters supported on single crystal titanium dioxide (110) surfaces in the oxidative dehydrogenation of methanol to formaldehyde. They will probe the catalytic activity as a function of both x and y to develop a model for the reaction mechanism. They will also prepare and study the catalytic activity of very small mass-selected, binary clusters such as palladium/gold and platinum/tin alloys of various compositions supported on single crystal titanium dioxide (110) surfaces in the synthesis of vinyl acetate and the selective hydrogenation of alkenes as a function of composition as well as develop a model for the reaction mechanism.A large number of industrial processes use nanometer-size clusters (both metal and metal oxide) supported on oxide surfaces to perform reactions that would not take place, or would be commercially unsuccessful if performed on the bulk material. In research supported by this grant the investigators will utilize state-of-the-art experimental and theoretical methods to probe the catalytic activity of well-defined nanocluster catalysts in great detail and develop a fundamental understanding of the catalytic chemistry at the atomic level. The concepts developed through this research will help optimize important industrial processes using these nanoscale catalysts and provide valuable insight into the discovery of new nanoscale catalytic materials. Researchers supported by this grant will also be active in outreach to K-12 schools in the Santa Barbara area. They plan to develop a tutorial presentation on an atomistic view of heterogeneous catalysis that will be included in the currently active outreach program in the department at UCSB. In addition, researchers working on this project will visit high schools in the Santa Barbara and Ventura Counties three times per year to discuss their research and its impact as well as to promote science education.