Oxygen coverage

As usual, things become more complicated when studied in detail. Note that for 0/W(l 10) 0 varies with 6 the situation is shown more fully in Fig. XVIII-15. The authors speculate that variations in Dq and E have to do with a p(2 x 1) structure at low oxygen coverage, with O atoms occupying alternate rows of W atoms, the empty rows becoming occupied above 0 = 0.5. The consequence is that O—O interactions shift from being mostly attractive to being in part repulsive. 

Other applications of REELM include monitoring variations like oxidation, segregation, and hydration in the surface chemistry of polycrystalline materials. Differences of 1 /10 of a monolayer in oxygen coverage due to variations in grain... 

Increasing catalyst potential and work function leads to a pronounced increase in total oxygen coverage (which approaches unity even at elevated temperatures) and causes the appearance of new chemisorption states. At least two such states are created on Pt/YSZ (Fig. 4.43) A strongly bonded one which, as discussed in Chapter 5, acts as a sacrificial promoter during catalytic oxidations, and a weakly bonded one which is highly reactive and causes the observed dramatic increase in catalytic rate. 

Figure 4.45. Thermal desorption spectra (bottom) and corresponding catalyst potential variation (top) after electrochemical O2 supply to Ag/YSZ at 260-320°C at various initial potentials Uwr Each curve corresponds to different adsorption temperature and current, thus different values of Uwr, in order to achieve nearly constant initial oxygen coverage.31 Reprinted with permission from Academic Press.

On the fuel-lean side (kadPo2 kpc2H4) the oxygen coverage is near unity and step (8.3) is the rate limiting step (rls). Thus equation (8.1) reduces to ... 

The TPRS and EELS results are interpreted as follows. The H2 desorption yield, a measure of the extent of C2H4 dehydrogenation, decreases linearly with increasing oxygen coverage, and the EELS re-... 

Figure 3a. CO2 evolution from the reaction of a molecular beam of CO with oxygen predosed onto Rh(l 10) to a coverage of 0.7 monolayers at a crystal temperature of 540 K, showing low reactivity at high oxygen coverage.

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