12CO adsorption

Fig. 28. Modifications of the IR spectrum of living polymer chains on stoichiometric a-Cr203 induced by CO solid curve, before 12CO adsorption dashed curve, after 12CO adsorption (p = 2.66 kPa) (Inset) Expanded view of the

Induces the formation of L - CO. The 12co - L species produced by CO adsorption can only arise from preadsorbed 12co-Bj species. 

Detailed Investigation of this B L conversion suggests that about 2Bi + 2L occur for each L - CO adsorbed. The stoichiometric relationship Induced by L - CO adsorption causing 2 i 2L Is shown In Figure 7, where Isotoplcally labeled CO has been employed In separate experiments as or as L. After a small correction Is made for the experimentally determined difference In extinction coefficient for 3co(ads) compared to 12co(ads), It may be seen that the stoichiometry 2B + L -> 3L Is closely verified. 

For the study of mixed oxides, one should characterize the various sites. In this case, the first step is to characterize the CO adsorption at various equilibrium pressures at low temperature, followed by evacuation at increasing temperatures to obtain information about the stabilities of the various species. Although the C—O stretching frequency is the most informative parameter, the data determining the stabilities of the various species can be decisive for the assignment of the bands. Multiple carbonyls adsorbed on the same metal cation are possible, and in order to identify them isotopic mixtures should be used. Sometimes the polycarbonyls are very stable and in this case, if 12CO is adsorbed first and then 13CO introduced, mixed species may not form at ambient temperature. 

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