Center for Functional Nanomaterials Seminar

It is essential to understand the growth, composition, and activity of catalysts on a fundamental atomic level in order to guide the development of future catalysts with higher product yield and selectivity. TiO2 supported bimetallic Pt-Au and Ni-Au clusters were studied as model catalysts for low temperature oxidation and epoxidation reactions. The properties of these model catalysts were investigated with scanning tunneling microscopy (STM), low energy ion scattering (LEIS), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption (TPD). The importance of the Au-titania interface for low temperature oxidation was illustrated by a series of TPD and STM experiments that show a direct correlation between the number of Au-titania interfacial sites and the activity on the surface. Bimetallic clusters were grown by first depositing Ni or Pt onto the surface in order to seed the more mobile Au at existing Ni or Pt clusters. The surfaces of the bimetallic clusters are significantly enriched in Au and are almost entirely pure Au for clusters with > 50% bulk Au composition. TPD of methanol and CO on bimetallic clusters that are highly enriched in Au at the surface still show significant activity characteristic of Ni or Pt at the surface, suggesting that methanol and CO are able to induce the diffusion of Ni and Pt to the surface of the clusters. The study of these model systems has provided valuable insight into the mechanism of oxidation reactions on several catalytic surfaces.