The oscillatory behavior of the CO oxidation reaction at atmospheric pressure over platinum single crystals: surface analysis and pressure dependent mechanisms

The oscillatory behavior of the catalyzed oxidation of carbon monoxide has been studied over platinum single crystals of (111), (100), and (13,1,1) orientation. Surface properties were examined in ultra high vacuum, before and after the reaction, using Auger Electron Spectroscopy (AES), Low Energy Electron Diffraction (LEED), and a Kelvin probe for work function measurements. The oxidation of carbon monoxide was carried out at both low pressure (10 −4 Torr) and atmospheric pressure. The mechanism for the oscillations was different at high and low pressures. A model is presented for the oscillations appearing in the high pressure reaction. This model invokes the formation of platinum oxide, the presence of which was determined experimentally. At atmospheric pressure, silicon was always present on the platinum surfaces and was necessary to detect oscillatory behavior.