| Abstract
| - Experiments were performed to understand the process of ignition during platinum catalyzed CO oxidationusing sum frequency generation (SFG) vibrational spectroscopy, Auger electron spectroscopy (AES), gaschromatography (GC), and temperature programmed desorption (TPD). Both CO dissociation and CO oxidationignition studies on the (100), stepped (557), and (111) surfaces of platinum are presented. Rapid CO dissociationon the Pt(100), Pt(557), and Pt(111) occurred in narrow temperature ranges (±10 K) at 500, 548, and 673 K,respectively. The CO ignition temperature at a pressure of 40 Torr of CO and 100 Torr of O2 is lower onPt(100) than on Pt(111) and Pt(557). Thus, both CO dissociation and the ignition of CO oxidation are structuresensitive. An in depth study of CO oxidation on Pt(557) was performed on both initially clean and initiallycarbon covered platinum surfaces to investigate the role of carbon obtained from CO dissociation in COoxidation. Under excess O2 and excess CO conditions, a clean platinum surface will remain carbon freebelow and above ignition. However, a carbon oxide species was formed on initially carbon covered platinumsurfaces once oxygen was added at a high temperature (548 K). This carbon oxide species results in a largeSFG background signal, allowing us to measure the formation and reactivity of this species during oxidationreactions. The carbon oxide species also formed on initially clean platinum below the ignition temperaturewhen the Pt crystal was exposed to equal partial pressures of CO and O2. The turnover rates on the carbonoxide covered platinum surfaces were higher than on the initially clean surfaces below ignition. The ignitiontemperature on the carbon covered surface (648 K) was lower than on the clean platinum (700 K) surface atequal pressures of CO and O2. All of this evidence indicates the surface carbon oxide species is better atoxidizing CO than platinum under certain pressure and temperature conditions. CO dissociation is an importantstep during the onset of ignition, when surface carbon oxidation provides a new exothermic reaction channelin addition to the Pt surface catalyzed oxidation of molecular CO.
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