| AVS 60th International Symposium and Exhibition | |
| Applied Surface Science | Thursday Sessions |
| Session AS+BI+EM+NL+NS+SS-ThA |
| Session: | Nanoparticle Surface Chemistry II |
| Presenter: | T.E. James, University of Washington |
| Authors: | T.E. James, University of Washington S.L. Hemmingson, University of Washington C.T. Campbell, University of Washington |
| Correspondent: | Click to Email |
The increasing demand for energy has accelerated the need to develop new and improved catalysts for existing and alternative technologies. Heterogeneous catalysts consisting of transition metal nanoparticles dispersed across oxide supports are found in solar cells, fuel cells, industrial chemical production and environmental cleanup. Fundamental understanding of these supported catalysts, such as the bond energies between the metal clusters and their supports, which is crucial to understand the sintering behavior and catalytic reactivity, is still largely missing. This work uses Cu clusters and a single-crystal ceria support as a well-defined model system to study the bond energies between metal clusters and the oxide support as a function of particle size. The adsorption energies and growth morphologies of Cu on CeO2-x(111) (where x= 0.05, 0.1 or 0.2) at 100 and 300 K were investigated using single crystal adsorption microcalorimetry together with x-ray photoelectron spectroscopy (XPS), ion scattering spectroscopy (ISS), Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and sticking probability measurements. Ceria thin films (~4nm) were grown on Pt(111) single crystal. The initial heat of Cu adsorption decreased with the extent of reduction of the ceria surface. The measured heat of adsorption increases with additional Cu deposition until it reaches the Cu bulk heat of sublimation (ΔHsub = 337 kJ/mol) at > 4 monolayers coverage. Interestingly, the Cu coverage required to reach ΔHsub decreases as the ceria surface is reduced. These results indicate that Cu adsorbs more strongly to ceria terraces than to oxygen vacancy sites, since the primary defect for reduced ceria surfaces is oxygen vacancies, but weakens the Cu-Cu bond for particles nucleated at terraces. The growth modes of Cu on CeO2-x(111) was also studied by XPS, ISS and AES. It was found that Cu grows as three dimensional particles on ceria. At 100 K the Cu particle density increased compared to 300K with a similar initial heat of adsorption, but took longer to reach the Cu heat of sublimation. The sticking probability was near unity for Cu adsorption on all these surfaces.