Carbon Monoxide Activation on Small Iron Magnetic Cluster Surfaces, FeCO, n = 1-20. A Theoretical Approach

The chemical activation of the carbon monoxide (CO) molecule on the surface of iron clusters Fe (n = 1-20) is studied in this work. By means of density functional theory (DFT) all-electron calculations, we have found that the adsorption of CO over the bare magnetic Fe (n = 1-20) clusters is thermochemically favorable. The Fe-CO interaction increases the C-O bond length, from 1.128 ± 0.014 Å, for isolated CO, up to 1.251 Å, for Fe₉CO. Also, the calculated wavenumbers associated with the stretching modes ν_CO are decreased, or red-shifted, as another indicator of the CO bond weakening, passing from 2099 ± 4 to 1438 cm^-1. Markedly, wavenumbers of vibrational modes ν_CO agree admirably well in comparison with experimental results reported for FeCO (n = 1, 18-20), getting small errors below 2.6%. The C-O bond is enlarged on the FeCO (n = 1-20) composed systems, as the CO molecule increases its bonding, charge transference, and coordination with the iron cluster. Therefore, small bare iron particles Fe (n = 1-20) can be proposed to promote the CO dissociation, especially Fe₉CO, which has been proven to obtain the most prominent activation of the strong C-O bond by means of the charge transference from the metal core.