Carbon monoxide oxygen coverage

Before analyzing the results of these, or similar, thermochemical cycles, the assumptions which have been made must be critically examined. Since the cycles are tested for different surface coverages, it is assumed first that the Q-0 curves represent correctly, in all cases, the distribution of reactive sites—the energy spectrum—on the surface of the adsorbent. This point has been discussed in the preceding section (Section VII.A). It is assumed moreover that, for instance, the first doses of carbon monoxide (8 = 0) interact with oxygen species adsorbed on the most reactive surface sites (0 = 0). This assumption, which is certainly not acceptable in all cases, ought to be verified directly. This may be achieved in separate experiments by adsorbing limited amounts of the different reactants in the same se-... 

Fig. 27. Differential heats versus coverage for the successive adsorptions, at 30°C, of carbon monoxide (A), oxygen(B), and, again, carbon monoxide (C) on the surface of lithium-doped nickel oxide. Reprinted from (54) with permission J. Chim. Phys.

Figure 9. Plot of the CO% production rate (divided by the coverages of oxygen and carbon monoxide) as a function of time for the titration of O by CO on Ir (111).

Beyer and coworkers later extended these reactions to platinum clusters Ptn and have demonstrated that similar reaction sequences for the oxidation of carbon monoxide can occur with larger clusters [70]. In addition, they were able to demonstrate poisoning effects as a function of surface coverage and cluster size. A related sequence for Pt anions was proposed by Shi and Ervin who employed molecular oxygen rather than N2O as the oxidant [71]. Further, the group of Bohme has screened the mononuclear cations of almost the entire transition metal block for this particular kind of oxidation catalysis [72,73]. Another catalytic system has been proposed by Waters et al. in which a dimolybdate anion cluster brings about the oxidation of methanol to formaldehyde with nitromethane, however, a rather unusual terminal oxidant was employed [74]. 

It can be concluded from the calorimetric data that the interaction between adsorbed oxygen and carbon monoxide is a multiple process. For low surface coverages—i.e., on the most active sites—CO " ions... 

Coverages resulting from activation in helium at 425° are about 1.1 molecules of oxygen or carbon monoxide per 100 A. We implicitly assume here that sites are distributed over the entire surface of the micropores. The coverages by carbon monoxide after conversion of chromia to microcrystalline a-CraOs by treatment with hydrogen at 450° are somewhat over 3 (Fig. 7), but the coverage by oxygen is only about 65% of that by carbon monoxide. 

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