In-situ detection of chemisorbed CO on a polycrystalline platinum foil using infrared-visible sum-frequency generation

Optical infrared-visible sum-frequency generation (SFG) surface vibrational spectroscopy was used for in-situ detection of CO adsorbed on a polycrystalline platinum foil in the range of 300-660 K at a CO pressure of 1 mbar under flow conditions. From the SFG spectra the frequency of the CO vibrationally resonant contribution was determined as a function of temperature. At 300 K a center-frequency of 2096 +/- 4 cm(-1) was obtained which is characteristic of the stretching vibration of CO 'on top'-bound at Pt terrace sites. At 660 K, the highest temperature where adsorbed CO could be detected on the foil, the center-frequency was 2057+/- 5 cm(-1) which can be attributed to CO molecules bound to defect-site PI atoms. Results obtained for the polycrystalline foil are compared with literature data for single crystal substrates. Results are presented where the SFG technique was applied for in-situ CO detection during heterogeneous CO oxidation on platinum over a pressure range of 10(-6)-10(3) mbar. (C) 1998 Elsevier Science B.V. All rights reserved.