| AVS 62nd International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS+AS+EN-WeA |
| Session: | Metals, Alloys & Oxides: Reactivity and Catalysis |
| Presenter: | Donna Chen, University of South Carolina |
| Authors: | D.A. Chen, University of South Carolina R.P. Galhenage, University of South Carolina K. Xie, University of South Carolina A.S. Duke, University of South Carolina H. Yan, Brookhaven National Laboratory |
| Correspondent: | Click to Email |
The nucleation, growth and chemical activity of bimetallic Pt-Re clusters on titania have been investigated as model systems for understanding Pt-Re catalysts for oxidation reactions. Scanning tunneling microscopy studies demonstrate that exclusively bimetallic clusters can be grown from the sequential deposition of Pt on Re or Re on Pt, provided that the deposition of the first metal creates a high enough cluster density for the nucleation of the second metal. Low energy ion scattering experiments indicate that the bimetallic clusters are Pt-rich regardless of the order of deposition. However, X-ray photoelectron spectroscopy (XPS) suggest that a Pt-Re alloy is formed from deposition of Re on Pt but not from Pt on Re. Furthermore, Re interacts more strongly with the titania support than Pt, resulting in reduction of titania. Temperature programmed desorption studies for CO desorption and methanol reaction confirm that the Re clusters have lower activity than Pt despite their higher surface area, and this behavior is attributed to oxidation of Re by the titania support. The alloyed clusters exhibit new activity for CO and H2 evolution that is not observed for the pure or unalloyed clusters. Methanol oxidation activity of these model surfaces are studied in a microreactor attached to an ultrahigh vacuum chamber so that the surfaces can be characterized by XPS before and after reaction. Specifically, changes in the oxidation states of Re in the bimetallic and pure Re clusters are investigated.