Copper surface coverage

Fig. 22 Top CV for Cu UPD on a R(ni) disk electrode in solution containing Br . Bottom ring-electrode currents recorded with the ring being potentiostated at —0.275 V. Insert copper surface coverages assessed from the disk electrode 0 ) and the ring electrode (9 ) during the positive-going sweep.

Figure 8.18. Surface coverages ofthe various intermediates on a copper surface during the water-gas shift reaction at 200 °C in a gas mixture of33% HjO, 52% Hj, 13%C02, and 1 % CO. Note the high coverage of formate at...

Analogous studies of the chemisorption of 14C-labeled benzene on copper powder and on platinum powder showed no chemisorption on the former, and the establishment of a low surface coverage over a range of temperature on the latter (Fig. 1). Again the surface coverage of hydrogen on platinum appeared to be about three times that achieved by benzene. 

We recall that the coverage dependent frequency shifts on copper surfaces are small. In the light of the preceding discussion possible explanations for this difference from the behaviour of CO on platinum and palladium include ... 

The g-factor for the surface trapped electrons was found to be g = 1.924, the same as in the unmodified Ti02 colloids. These trapping sites are not significantly affected by adsorption of alanine, probably because of the low surface coverage of alanine. However, in the presence of copper, heating of the sample to room temperature resulted in the disappearance of the signal for trapped electrons. Under die same conditions, the reduction of copper ions to a metallic state was confirmed using X-ray absorption spectroscopies (XAS) [27]. 

The two phase model describes all the principle features of the desorption kinetics, suggesting that recombinative desorption under conditions where the coverage is less than saturation occurs by the recombination of N atoms from a dilute phase on the Cu(l 11) surface. This behaviour is the same as that observed for H recombinative desorption on many surfaces [63]. Desorption from the dilute phase is preferred over direct decomposition of the nitride islands because this leaves the copper surface in its equilibrium (111) orientation, rather than as an unstable Cu(l 00) overlayer [99]. As a result we expect that detailed balance can be used to relate measurements of recombination from the N covered Cu(l 1 1) surface with nitrogen dissociation on bare Cu(l 1 1) terraces. In contrast, if desorption occurred via decomposition of reconstructed copper nitride islands then detailed balance arguments would not reveal anything about the energetics or dynamics of N2 dissociation on a Cu(l 1 1) surface. 

The isosteric heats of adsorption for nitrogen on the (110), (100), and (111) single crystal faces of copper and on polycrystalline copper surfaces calculated from the adsorption isotherms by the author at 78.1-83.5, 78.1-89.2, and 83.5-89.2°K. are plotted as a function of surface coverage in Fig. 31. The horizontal and vertical lines indicate the maximum experimental uncertainties in the values of (II) and (0), respectively. The average of the corrected xm values from Table IV was used for each temperature pair to calculate values of (0). The values for xj are the values for xm corrected for the variation of the density of the adsorbate with temperature below the critical temperature. Representative curves were drawn through a very large number of points. The latter... 

The heats of adsorption of nitrogen on evaporated metal films of nickel and iron have been reported to decrease from 10 to 5 kcal./mole as the surface coverage increased from about 0.1 to 1.0 monolayer. Beeck (150) states that nitrogen is unsuitable for the evaluation of surface areas of evaporated iron and nickel films by the Brunauer-Emmett-Teller method because of its high heat of adsorption at 78°K., which would yield a value for monolayer adsorption too high by 50%. The author feels that this objection does not apply to the nitrogen adsorption on reduced electropolished planar copper plates for the following reasons. 

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