Chemistry Department Seminar

The nucleation, growth and surface composition of Au-based bimetallic clusters (Au-X where X=Ni, Pt, Co) on titania have been investigated as model systems for understanding how surface chemistry can be controlled by bimetallic composition and interactions between the clusters and the oxide support. Scanning tunneling microscopy studies demonstrate that bimetallic clusters are formed by seeding the mobile Au atoms at existing Ni, Pt and Co clusters due to the higher mobility of Au atoms compared to the second metal. The cluster surfaces are almost pure Au at Au compositions greater than 50%; however, adsorbates such as CO and methanol induce diffusion of Ni and Pt to the cluster surface. After heating to 800 K, the Ni and Pt in the bimetallic clusters become selectively encapsulated by titania while the Au remains at the cluster surface. The resulting clusters have an extended network of Au-titania sites, which are believed to be the active sites in oxidation reactions on titania-supported Au clusters. The nature of the Au-titania interfacial sites is probed by methanol reaction since the production of formaldehyde is believed to occur at the Au-titania interface.