Extinction coefficients and integrated intensities for linear- and bridged-bonded CO on platinum

Abstract

For the first time, infrared integrated absorption intensities and extinction coefficients have been determined for both the linearly adsorbed (high frequency-HF) and the bridged-bonded (low frequency-LF) forms of CO on Pt. Platinum dispersed on η-Al2O3, SiO2, SiO2–Al2O3, and TiO2 was characterized by both hydrogen and CO chemisorption which allowed the determination of individual surface coverages of the two CO species. The integrated intensities A for the HF species were 9–19×107 cm mol−1 for typical Pt catalysts (using SiO2, Al2O3, and SiO2–Al2O3) while A values over 30×107 cm mol−1 were measured for the TiO2-supported catalysts. Integrated intensities for the LF form were always lower on a given catalyst and ranged from 2 to 25×107 cm mol−1. Similarly, extinction coefficients ε at the HF band maxima were always higher than those for the LF species. Values for εHF fell between 0.6 and 2.1×106 cm2 mol−1 while εLF values ranged from 0.1 to 0.5×106 cm2 mol−1 for the typical catalysts. The higher values for the titania-supported catalysts may be a consequence of SMSI (strong metal-support interaction) behavior which alters the electronic state of the Pt and, as a consequence, the CO surface coverage.