Adsorption of oxygen on nickel

Fig. 19. Differential heats of adsorption of oxygen on nickel oxide, NiO (200), at 30°C. Reprinted from (19) with permission. 

It is, of course, not necessary to use a heat-flow microcalorimeter in order to determine the heat released by rapid adsorption phenomena. Dell and Stone (74), for instance, using an isoperibol calorimeter of the Garner-Veal type, found an initial heat of 54 4 kcal mole-1 for the adsorption of oxygen on nickel oxide at 20°C. The agreement with the value (60 2 kcal mole-1) in Fig. 19 is remarkably good, particularly if it is considered that very different methods were used for the preparation of the nickel-oxide samples (19, 74)-... 

G. Parravano University of Notre Dame) It is interesting to note that the results on the adsorption of oxygen on nickel obtained by electron diffraction are consistent with the conclusions reached in a thermodynamic study of the same process ). In this study it was found that even at low... 

Fig. X. Hydrogen adsorption at 78° and 300°K as a function of preadsorbed amount of oxygen on nickel.

In conclusion, we would like to point out the possibility that an effect similar to that described above, a correlation between the adsorption of gases and surface imperfections present, may occur on other materials. For example, Schuit and de Boer (52) have found that slow adsorption of hydrogen on nickel is found only if there is oxygen on the surface. 

Adsorption of Oxygen on Pure and Doped Nickel Oxides at 30"... 

The adsorption of CO2 on metallic nickel films has been studied in both the presence and absence of oxygen. An i.r. spectroscopic study of the simultaneous adsorption of COg and O2 on nickel has shown the formation of carbonate-carboxylate structures on the nickel surface. The adsorption of CO2 on nickel in the temperature range —196 to 0 °C has been found to be irreversible, the molecules being adsorbed at two surface sites within the limits of the monolayer. Above 100 °C, dissociative adsorption of CO2 takes place with the formation of CO. ... 

Tarasevich MR, Vilinskaya VS, Khutomoi AM, Burshtein RKh, Makordei FV, Tkach YuA. Adsorption and electroreduction of molecular oxygen on oxide catalysts H mechanism of cathodic reduction of oxygen on nickel cobaltate (NiCo204). Elekfrokhimiya 1976 12 504-7. 

Adsorption of benzene on sulfur- and oxygen-contaminated (110) faces of nickel revealed that the ordered layers formed differed from those obtained at the clean Ni(110) surface (23, 29). 

Fig. 2. Typical curves of the relative changes of the electrical resistance of nickel films as a function of time (a) adsorption of one dose of hydrogen on the surface, partially covered by preadsorbed oxygen (b) adsorption of one dose of oxygen on the surface, covered by preadsorbed hydrogen (both at 300°K).

Calvet microcalorimeters are particularly convenient for such studies. Figure 19 show s, for instance, the evolution of the differential heat of adsorption of oxygen, measured at 30°C with a Calvet calorimeter, as a function of the total amount of oxygen adsorbed on the surface of a sample (100 mg) of nickel oxide, NiO(200) (19, 73). The volume of the first... 

Fig. 22. Differential heats of adsorption of oxygen at 30°C on four different samples of pure and doped nickel oxide, (a) NiO (200), (b) NiO(Li) (250), (c) NiO (250), (d) NiO(Ga) (250). Reprinted from (8) with permission. Copyright 1969 by Academic Press, Inc. New York.

Carbon monoxide oxidation is a relatively simple reaction, and generally its structurally insensitive nature makes it an ideal model of heterogeneous catalytic reactions. Each of the important mechanistic steps of this reaction, such as reactant adsorption and desorption, surface reaction, and desorption of products, has been studied extensively using modem surface-science techniques.17 The structure insensitivity of this reaction is illustrated in Figure 10.4. Here, carbon dioxide turnover frequencies over Rh(l 11) and Rh(100) surfaces are compared with supported Rh catalysts.3 As with CO hydrogenation on nickel, it is readily apparent that, not only does the choice of surface plane matters, but also the size of the active species.18-21 Studies of this system also indicated that, under the reaction conditions of Figure 10.4, the rhodium surface was covered with CO. This means that the reaction is limited by the desorption of carbon monoxide and the adsorption of oxygen. 

However, there is another consideration which has worried this author as early as 1937 when he and his coworkers measured the adsorption isotherm of nitrogen on nickel and iron at liquid oxygen temperature and found that the isotherm was essentially flat between 10-4 and 10 l mm. Hg pressure. It was about this time that the Emmet-Brunauer method was first made public, and off hand the two results appeared to be irreconcilable. This uncertainty was aggravated by the fact that the nitrogen adsorption isotherm as published by the author and his Coworkers could at that time not be extended to pressures higher than... 

Iron films behave in every way similar to nickel films except that upon admitting oxygen, about seven oxygen atoms are sorbed instantaneously for every crystallographic site, forming an iron oxide film seven atom layers deep, and except that the heat of adsorption of hydrogen on such an oxide covered film is almost identical with that on the clean iron surface even immediately after the oxidation has taken place. 

Hi. Zeolites exchanged with transition metal ions. In the first row, scandium-, titanium-, cobalt-, and nickel-exchanged zeolites have been the most studied. Cobalt-exchanged zeolites are discussed in Section IV,E since they lead to oxygen adducts on adsorption of oxygen. There are several cases where copper and particularly iron ions are found as impurity cations which affect the oxygen adsorption properties of the zeolite. 

IV. Adsorption of Oxygen and Oxidation Catalysis on Nickel Oxide. 60... 

To sum up, the available data relative to oxygen adsorption or catalysis on nickel oxide show the existence of two types of chemisorbed oxygen, one of them being related to the ability of this oxide to accommodate excess oxygen. The evidence concerning this latter property will now be reviewed with emphasis on the defect structure of bulk nickel oxide. 

The active sites for the oxygen adsorption, which are found on the surface of NiO (250) but not of NiO (200), are to be identified with anionic vacancies because this high heat of adsorption is not caused by the sorption of oxygen on the nickel phase (13). The decrease in the capacity for adsorption of oxygen at 30°C. when the temperature of oxide preparation is increased from 200° to 250°C. is explained by the reduction of surface nickel ions, sites for the adsorption only of oxygen, and the formation of nickel crystallites whose surface atoms may be active towards the adsorption of oxygen at 30°C. Recession of nickel ions below the surface for NiO (250) may also contribute to this decrease. 

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