Development of advanced model catalysts: A study of catalysis over epitaxially grown titanium oxide films, palladium foils and platinum nano-particle arrays.

摘要

Titania overlayers were grown in two different ordered structures on Pt(111) as seen by Low Energy Electron Diffraction (LEED). Fully oxidized, films maintain the symmetry of top layer of the substrate and form a coincident 18.2 A unit cell. These overlayers could be grown in monolayer and multi-layer coverages. They are seen by X-Ray Photoelectron Spectroscopy (XPS) to have TiO{dollar}sb2{dollar} stoichiometry. Above 400{dollar}spcirc{dollar}C the oxide disproportionates and titanium migrates into the bulk to form an alloy. The LEED and XPS data are consistent with the model of a close-packed lattice of oxygen anions with titanium cations in the octahedral sites.; Vacuum annealing above 600{dollar}spcirc{dollar}C forms a partially reduced monolayer with the stoichiometry Ti{dollar}sb4{dollar}O{dollar}sb7.{dollar} This overlayer does not have the symmetry of the substrate. The unit cell is given by the coincidence of the substrate lattice with a rectangular cell of 3.5 A x 4.2 A. Ion Scattering Spectroscopy data suggests the structure is formed upon creating oxygen vacancies.; Ethane oxidation was performed over palladium foils under a wide range of reactant concentrations to produce CO{dollar}sb2{dollar}, H{dollar}sb2{dollar}O, CH{dollar}sb4{dollar} and C{dollar}sb2{dollar}H{dollar}sb4.{dollar} The foils required an initial activation period at high temperature ({dollar}>{dollar}400{dollar}spcirc{dollar}C) under fuel rich reaction conditions. Methane and CO{dollar}sb2{dollar} displayed similar kinetics although methane was produced with {dollar}sim{dollar}1/85{dollar}sp{lcub}rm th{rcub}{dollar} the rate. Ethylene was a reaction intermediate and eventually converted to CO{dollar}sb2.{dollar} Depending on their concentration, water and oxygen inhibited combustion. A mechanism consistent with the observed kinetics is proposed in which the rate determining step is ethyl formation on a Pd-PdO or PdO-PdO two-atom site.; Electron Beam Lithography was used to fabricate nanometer-scale arrays of platinum particles on an oxidized silicon wafer. Low energy ion bombardment was used to clean the array, which was then active for ethylene hydrogenation with rates comparable to the literature. Thermal desorption experiments demonstrated the possibility of metal-to-support spillover. With these activation procedures lithographic methods can be used to fabricate nanometer-scale, spatially controlled model catalysts.