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

化学催化计划支持来自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，其共同特征是非常小，孤立，明确的催化活性位点。研究人员设计并构建了一种独特的，高度通用的设备，该设备允许通过将质量选择的纳米团簇从气相沉积到单晶氧化物载体上来生产模型催化剂（金属和金属氧化物）。这些定义明确的纳米簇催化剂的特点是使用一个正常的阵列的表面科学方法，此外，利用超真空结合扫描尖端显微镜（UHV-STM）的方法来探测反应前后的纳米簇的大小和形状。在UHV中使用程序升温脱附（TPD）和程序升温反应（TPR）以及在升高的压力下使用附接到表面科学室的高压间歇反应器来监测这种模型催化剂的化学性质。具体来说，研究人员将准备和研究在甲醇氧化脱氢为甲醛的过程中，负载在单晶二氧化钛（110）表面上的非常小的质量选择性簇合物的催化活性。他们将探测催化活性作为x和y的函数，以开发反应机制的模型。他们还将准备和研究催化活性的非常小的质量选择，在合成乙酸乙烯酯和烯烃的选择性氢化中，负载在单晶二氧化钛（110）表面上的各种组成的二元簇如钯/金和铂/锡合金作为组成的函数，并开发了反应机理的模型。使负载在氧化物表面上的团簇（金属和金属氧化物）尺寸化，以进行不会发生的反应，或者如果在块体材料上进行则在商业上不成功。在这项资助支持的研究中，研究人员将利用最先进的实验和理论方法来详细探索定义明确的纳米簇催化剂的催化活性，并在原子水平上对催化化学进行基本了解。通过这项研究开发的概念将有助于优化使用这些纳米催化剂的重要工业过程，并为发现新的纳米催化材料提供有价值的见解。 由这笔赠款支持的研究人员也将积极推广到圣巴巴拉地区的K-12学校。他们计划开发一个关于多相催化的原子论观点的教程演示，该演示将包括在UCSB部门目前活跃的外展计划中。此外，从事该项目的研究人员将每年三次访问圣巴巴拉和文图拉县的高中，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.