Estimation of CO heats of adsorption on metal surfaces from vibrational spectra
- Pennsylvania State Univ., University Park, PA (United States)
The study of CO chemisorption on metal surfaces is, in general, of extreme fundamental importance for understanding of bonding mechanisms and of practical importance because of the use of CO in NO{sub x} reduction catalysts and Fischer-Tropsch synthesis reactions. An empirical relationship between the bond dissociation energy at 0 K, D{sub 0}, and the force constant, k, was obtained for a series of heteronuclear carbon-containing and homonuclear metal diatomic species, suggesting that the potential wells for these species have similar curvature. This D{sub 0}-k relationship was then used as part of a simple mathematical formalism to calculate the metal-carbon and carbon-oxygen bond strengths of Co adsorbed on metal surfaces directly from experimental values of A{sub 1} vibrational modes. By assuming a rigid metal lattice, whose bonds remain unperturbed as a result of Co adsorption, it was thus possible to directly calculate the heat of adsorption of CO, Q{sub ad}, from the calculated bond strengths. Although calculated values of Q{sub ad} for CO on 3d and 4d transition metals were in reasonable agreement with experimental values reported in the literature, agreement was not satisfactory for the 5d transition metals. Further analysis indicates that the discrepancy is likely due to the assumption of a rigid metal lattice and that Co adsorption on some metal surfaces, particularly those of platinum and iridium, induces some bond relaxation on the metal surface. It is thus suggested that metal surfaces which have both a large curvature of the cohesive function and adsorb CO primarily via 5{sigma} donation to the surface, i.e., little metal back-bonding, are strongly susceptible to bond relaxation and possible reconstruction.
- OSTI ID:
- 376247
- Journal Information:
- Industrial and Engineering Chemistry Research, Vol. 35, Issue 9; Other Information: PBD: Sep 1996
- Country of Publication:
- United States
- Language:
- English
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