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?Vibrational frequencies of CO adsorbed on silica-supported Mo atoms from density functional calculations?: a re-interpretation of results reported by N. L�pez, F. Illas, G. Pacchioni

“…Thus, we maintain our conclusion [2] that the blue shifted 2170 cm −1 band is diagnostic of the presence of Mo(II) surface sites in the catalyst, as we shall discuss below.…”

“…No peaks due to adsorption of CO on states C and D were detected by FTIR; in the case of B, the band at 2170 cm −1 was observed. Note that this peak disappeared completely and readily upon evacuation at room temperature of the gas adsorption cell and was fully restored after re-admission of CO [2]. After 24 h of exposure to CO under either natural or artificial light illumination, a peak at 1990 cm −1 and several other minor ones between 2125 and 2035 cm −1 developed at the expense of the initial 2170 cm −1 signal.…”

“…After 24 h of exposure to CO under either natural or artificial light illumination, a peak at 1990 cm −1 and several other minor ones between 2125 and 2035 cm −1 developed at the expense of the initial 2170 cm −1 signal. The peak at 2170 cm −1 was assigned [2] to CO adsorbed on the dominant (>90%) Mo(II) species measured by XPS in state B [3]. It was further suggested, on account of the positive shift in ν(CO), that bonding to the surface sites should be of a character and rather weak, with no reinforcement by back donation ( bonding).…”

“…On the other hand, in our previous work [2,3] the notation Mo n+ designated the +n O-S of a real species (as probed by XPS). It was assumed that such species are of the type described by López et al as neutral, because they should be more stable than the charged ones.…”

“…FTIR was employed to measure the vibrational frequencies of CO adsorbed on catalysts in the states represented by B, C, and D [2], with the aim of finding correlations between the O-S of well defined surface species and the vibrational frequency of CO adsorbed on such species. No peaks due to adsorption of CO on states C and D were detected by FTIR; in the case of B, the band at 2170 cm −1 was observed.…”