Chemistry Graduate Seminar by Professor Barry Cheung
Title: Nanostructured catalyst design using reducible oxides and metal clusters
Abstract:
Engineering metal clusters on reducible oxide supports has been an emerging topic in new heterogeneous catalyst designs. The strong interactions of the metal clusters on different reducible oxide supports were found to greatly enhance and alter the catalytic activity of the metal clusters. Oxygen vacancy defects (OVDs) have been suggested to strongly influence the oxidative catalytic activity in ceria (CeO2) and its interaction with metal clusters. In this talk, we will report our study of the defect engineering of cerium oxide nanorods (nanoceria, CeO2-x, 0 ≤ x ≤ 0.5) and its applications to generate highly active metal (gold and palladium) clusters decorated ceria catalysts. We will illustrate the application of low pressure thermal annealing to increase the density of OVDs in ceria nanorods and enhance their oxidative catalytic activity. The high density of OVDs in these nanorods is revealed by high resolution transmission electron microscopy and also indirectly suggested by the decrease in the average bond length of Ce-O and the coordination number of the first Ce-O shell in our extended x-ray absorption fine structure study. Significantly, these low pressure activated ceria nanords are found to have larger Ce3+/Ce4+ ratios in their chemical composition and higher oxidative catalytic activity towards carbon monoxide oxidation than those of the atmospheric pressure activated ones and the bulk samples. Low contents of gold and palladium clusters decorated on the highly defective ceria nanorods are found to stabilize and increase the OVD density and the oxidative catalytic activities in these nanorods. Hypothesized first principle models for possible explanations for roles of metal clusters and atoms in the stabilization of OVDs in these nanoceria and the enhanced oxidative catalytic activity of these decorated nanostructured ceria will be presented. Lastly, we will discuss the bifunctional activity of nanoceria enabled by the coordinatively unsaturated Ce sites exposed by the oxygen vacancy defects and the adjacent active surface oxygen atoms for the cyanosilylation of aldehydes with trimethylsilyl cyanide.
About the speaker:
Professor Barry Cheung got his BS degree from University of Wisconsin, Madison, and PdD degree from Harvard University. Currently he is an assistant professor in the department of chemistry, University of Nebraska-Lincoln.
The research in Professor Cheung’s group involves the design and synthesis of inorganic/bio-organic nanostructured components that can self-assemble into 3-dimensional hierarchical structures with novel physical and chemical properties. The strategy is to abstract the efficient designs from nature to guide the synthesis of self-assembled components of materials systems
