| AVS 64th International Symposium & Exhibition | |
| Surface Science Division | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Poster Session |
| Presenter: | Vikram Mehar, University of Florida, Gainesville |
| Authors: | V. Mehar, University of Florida, Gainesville C. Wu, University of Florida, Gainesville M. Shipilin, Lund University, Sweden E. Lundgren, Lund University, Sweden H. Gronbeck, Chalmers University of Technology, Sweden A. Ashtagiri, The Ohio State University J.F. Weaver, University of Florida, Gainesville |
| Correspondent: | Click to Email |
Palladium has been extensively used to promote the catalytic combustion of methane and CO oxidation in automotive exhausts. It has been observed that formation of metal oxide layers can significantly alter the surface reactivity due to differences in chemical properties of oxide and metal surface. Understanding the reactivity of oxides formed under different growth conditions could facilitate the design of catalysts attuned for specific applications. In this presentation, I will discuss results of our studies of Pd(100) oxidation by atomic oxygen as well as the adsorption and oxidation of CO on single-layer and multilayer PdO structures. We find that a well-ordered PdO(101) film of about 7 ML thickness develops on Pd(100) during oxidation with O-atoms at 500 K, whereas a thicker PdO structure (~14 ML) with an apparently more rough morphology grows at temperatures above 600 K. LEED shows that the multilayer PdO(101) structure adopts the same epitaxial relationship with the Pd(100) substrate as the so-called √5 surface oxide, which has been previously shown to correspond to a single layer of PdO(101).
Although the surface structures are nominally identical, temperature-programmed reaction spectroscopy (TPRS) and reflection-absorption infrared spectroscopy (RAIRS) measurements show that the single layer and multilayer PdO(101) structures exhibit distinct reactivity toward CO. TPRS shows that the multilayer PdO(101) structure is more reactive toward CO compared with the single layer PdO(101). Also, RAIRS shows that CO binds only in an atop configuration on the coordinatively-unsaturated (cus) Pd atoms of the multilayer PdO(101) structure, whereas CO initially populates bridging Pd sites on the single PdO (101) layer before also occupying atop Pd sites at higher CO coverages. I will also present results of density functional theory calculations that clarify the origins the different chemical reactivity of the single and multiple layer PdO(101) structures toward CO.