| AVS 62nd International Symposium & Exhibition | |
| Surface Science | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Poster Session |
| Presenter: | Randima Galhenage, University of South Carolina |
| Authors: | R.P. Galhenage, University of South Carolina K. Xie, University of South Carolina H. Yan, Brookhaven National Laboratory G. Seuser, University of South Carolina D.A. Chen, University of South Carolina |
| Correspondent: | Click to Email |
The study of metal clusters on single-crystal oxide supports as model systems has garnered much attention for fundamental investigations of catalytically active surfaces that can guide the rational design of new catalysts. For instance, Pt-based catalysts have been recently proposed for the aqueous phase reforming of alcohols but suffer from a lack of stability due to poisoning by CO and other carbonaceous species. The addition of a second metal, such as Re, to Pt has been shown to increase the stability and the activity of the catalyst, but the exact reason behind this enhanced activity is not well understood. To better understand this bimetallic system, we have prepared model catalysts consisting of bimetallic Pt-Re clusters on TiO2 to investigate the growth of metals, metal-metal interactions, metal-support interactions and activity using Scanning Tunneling Microscopy (STM), X-ray Photoelectron Spectroscopy (XPS), Low Energy Ion Scattering Spectroscopy (LEIS) and Temperature Programmed Desorption (TPD). Re shows strong metal support interactions (SMSI) even at room temperature, resulting in highly dispersed 2D clusters. Encapsulation of Re by TiOx was observed due to SMSI effects. Pt-Re bimetallic clusters were prepared by depositing the less mobile Re first followed by deposition of Pt for submonolayer coverages. The surface composition of the bimetallic clusters was Pt-rich due to the lower surface free energy of Pt and the oxophillic nature of Re. CO adsorption behavior of the bimetallic clusters resembled the activity of pure Pt. At higher coverages (3.7 ML total metal coverage) bimetallic clusters were formed by both orders of deposition, Re on Pt and Pt on Re. When Re was deposited first, it resulted in a higher nucleation density for the bimetallic clusters with 100% Pt at the surface, and the activity resembled that of pure Pt. When Pt was deposited first, the initial seed cluster density was low, resulting in a lower density of bimetallic clusters, which led to a smaller number of active sites. In this order of deposition, the surface composition was a mixture of Pt and Re, and the activity studies suggest that both Pt and Re are active sites for the adsorption of CO. Pt-Re interactions were observed when Pt was deposited on titania followed by the deposition of Re.