INFRARED REFLECTION ABSORPTION-SPECTROSCOPY OF ADSORBATES ON A PT(100) SURFACE DURING CO OXIDATION

The infrared spectra of adsorbates and partial pressures of CO, O2, and CO2 taken in situ during CO oxidation on a Pt(100) surface are reported. At 400 and 430 K three bands are observed in the infrared spectrum. The first band at approximately 1630 cm-1 is assigned to a complex involving adsorbed CO and adsorbed oxygen. This complex is a precursor to CO2 formation. The second and third bands at approximately 2087 and 1880 cm-1 are assigned to CO adsorbed on top and bridge sites ordered in a (square-root 2X square-root 2)R45-degrees adlayer. At 460 K the [CO-O] complex band is not seen in the infrared spectrum because the rate of reaction of the complex is much faster than the rate of complex formation. Small islands of adsorbed CO (approximately 10 angstrom on an edge) are inferred from the infrared spectrum in the reaction rate region of high CO2 production. The variation of the [CO-O] complex band with temperature and CO island size is presented. The [CO-O] complex band sharpens with decreasing temperature and increasing CO island size.