Transient Fourier transform infrared spectroscopy (FTIR) spectroscopy and mass spectroscopy were used in tandem to study CO adsorption and kinetic rate oscillations in the oxidation of CO at intermediate pressure (1-10 Torr) on a series of silica gel-supported platinum catalysts of varying dispersion and preparation. FTIR shows that the stretching frequency of linearly bonded CO decreases as the dispersion of the platinum particles increases (2076 cm(-1) for D = 25% to 2058 cm(-1) for D = 99%), but CO bonded to electron-deficient platinum (CO-Ptdelta+) results in a frequency of similar to 2080 cm(-1) for all particle sizes. Isotope-mixing experiments and dipole coupling simulations were performed in order to determine the dipole and chemical components of the coverage-dependent IR peak shift on supported platinum. The results compare favorably to single-crystal studies and show a chemical shift of 10 cm(-1) and a dipole shift of 25 cm(-1) that are independent of particle dispersion. Reaction studies at T = 180-300 degreesC and O-2:CO = 0.5-4.0 suggest that the oxidation/reduction model and the carbon deposition model cited in the literature are both inadequate to explain the observed oscillations over these catalysts. A mechanism is suggested in which densely packed islands of CO block a portion of the active sites during the reaction. Differences in catalyst precursor (chloroplatinic acid or tetraammine platinum(II) nitrate) affect the amplitude of the oscillations observed in this study. The feedback mechanism driving the oscillations remains unclear but is most likely related to the Pt(100) or Pt(110) surface-phase transition or chlorine impurities supporting the formation of islands through electrostatic interaction.