This CAREER award by the Analytical and Surface Chemistry Program in the Division of Chemistry supports work by Professor Uwe Burghaus at North Dakota State University Fargo to characterize the adsorption dynamics of small molecules (carbon monoxide, dioxide and oxygen) on Cu and Au model array catalysts which are pertinent for the petroleum industry and the cleaning of exhaust pollution, and to clarify with molecular beam scattering the catalytic activity and particle size, as well as support effects, in the CO oxidation reaction mechanism. This reaction is one of the most important prototypes of bimolecular surface reactions. The knowledge gained will promote catalyst improvements.
This project includes a large number of students recruited from diverse locations including graduate students from NDSU, undergraduates from tribal colleges, and students from a local non Ph.D. granting college. Some of the experiments will be conducted as part of a physical chemistry laboratory class providing an introduction about nanoscience and kinetics to the students. A related off-campus hands-on class will be taught at a Native American community college (Sunday Academy).
According to estimates at least 60% of the industrial products and 90% of chemical transformations are based on catalysts. Most large scale catalytic processes are heterogeneously catalyzed (gas-surface/solid interactions) due to easier separation of products, reactants, and catalyst. This is the area of our research. We aim towards an atomic level understanding of basic heterogeneously catalyst processes. In model studies, typically crystalline surfaces or small agglomerates (clusters) are studied. These crystalline systems consist of well-defined sites where gas phase species can adsorb, as chess pieces on a chess board. Since the early days in catalysis and surface science, it has been proposed that special sites exist on catalyst surfaces where the chemical transformations take place, termed the "active sites". Our goal was to find and characterize these actives sites on model catalysts. In order to predetermine the active sites, but still work on realistic model systems, so-called electron beam lithography (EBL) was used to nanofabriate the catalysts. With that technique simple pattern of nano-sized clusters, consisting of copper, gold, molybdenum and their oxides were nanofabricated and deposited on silica supports. Analytic surface science techniques were used to characterize these model catalysts. It turned out, for example, that CO2 molecules adsorb solely along the rim of these Cu agglomerates, i.e., the active sites were indeed identified. In contrast, CO adsorbs non-specifically on all available adsorption sites. Now, the size of these agglomerates can determine the ratio of active to non-active sites allowing for catalyst tuning via cluster size variations. Indeed, we observed cluster size dependent catalytic activity for gold clusters. The concept of active rim sites is already used in industry to fine-tune catalyst of commercial interest. Another important component of our projects is educational. For example, an on-line class about surface science, nanoscience, and materials was developed. In addition, students at all levels (from high school students to postdoctoral associates) were trained in the use of analytic surface science tools in the research lab. We worked together with the Governor's school program as well as NATURE (Nurturing American Tribal Undergraduate Research and Education) program. Students supported by this project graduated with Ph.D. degrees and all found their way into the workforce.
