Chemisorption studies of oxygen-containing molecules on Au(211), Pt(111) and Sn-modified Pt(111) surfaces.

摘要

Modern analytical techniques in surface science to advance and allow for the investigation and elucidation of the science of catalysis. Metal-based heterogeneous catalysts play a central role industrially, yet a fundamental understanding of what controls selectivity of these catalysts is still forthcoming. Surface science techniques have been used in this thesis to study the adsorption of oxygen-containing molecules on several metal surfaces.; Adsorption of O₂, O₃ and CO were investigated on the stepped Au(211) surface. No oxygen adatoms were found on the surface by adsorbing O₂ under UHV and high pressure condition. However, O ₃ created oxygen adatoms on the surface at step and terrace sites with different desorption energies. CO adsorbed weakly, molecularly on Au(211) at 85 K. CO also revealed two different kind of adsorption sites. IRAS identified CO adsorption at atop sites. CO oxidation on the O-precovered Au(211) was performed at 85–400 K with an apparent activation, E_app = −1.0 kcal/mol, similar to Au(111).; EtO adsorption was investigated on Pt(111) and two, ordered surface alloys, p(2 x 2) and (√3 x √3)R30° Sn/Pt(111). EtO didn't decompose on the Pt(111) and Sn/Pt(111) surface alloys except minor decomposition due to defect sites. HREELS indicated that EtO existed as a molecular form even at small coverage. UPS spectra confirmed that EtO adsorbed on the surface via oxygen atom. Additionally, EtO adsorption was studied on the stepped Au(211) surfaces. TPD spectra revealed two different adsorption sites. IRAS showed that EtO existed as a molecular form at low coverage and axis of EtO was parallel to the surface normal.; Tin-oxide films have been studied for developing toxic gas sensors and fuel cell. Tin-oxide films were grown on Pt(111) substrates by oxidation of Sn/Pt surface alloys using NO₂ exposures or by deposition of Sn in an NO₂ ambient gas. XPS confirmed the existence of three Sn, metallic, oxidic Sn, and “quasimetallic” which results from oxidized Sn that is still alloyed within the Pt surface layer. UPS identified a SnO ₂ stoichiometry for multilayer films. HREELS was used to identify characteristic vibrational modes for the different monolayer films. SnO₂ crystallites, although only a few monolayers high and tens of nanometers in width, remarkably exhibit bulk-like vibrational and electronic properties.