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

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

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.