The isotopic exchange of CO adsorbed on Pt(111) was studied using polarization modulation IR reflection absorption spectroscopy (PM-IRRAS) and temperature programmed desorption. It was found that the rate constants for the exchange reaction are much higher than would be expected from previous investigations of CO adsorbed on Pt narroparticles. The adsorption of CO on Pt(111) under elevated pressures of CO and H-2 was also studied using PM-IRRAS. It was seen that CO pressures above 1 mbar lead to a shift in the absorption peak arising from CO adsorbed on a bridge site from 1850 to 1875 cm(-1). Exposing the CO-covered Pt(111) surface to 1000 mbar H-2 did not lead to any significant desorption of CO at room temperature, whereas at 363 K H-2 exposure did lead to a significant desorption of CO, due to the increased chemical potential of H-2. In a mixture of CO and H-2 with partial pressures of 0.01 mbar and 1000 mbar, respectively, no significant effect of H-2 on the PM-IRRAS spectrum was seen at temperatures below 423 K.