Oxygen on nickel oxide

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)-... 

Fig. 7a. Rate of chemisorption of oxygen on nickel oxide at 25°C and at various oxygen partial pressures, according to Engell and Hauffe. The chemisorbed volume in cubic centimeters is plotted against log (< + Zo), where (is the time of chemisorption in minutes, and to a constant.

The surface reaction of carbon monoxide and oxygen on nickel oxide 16) and on cobalt oxide 17) was also investigated by the same method of... 

Oxygen evolution occurs on nickel oxide electrodes throughout charge, on overcharge, and on standby. It is the anodic process in the self-discharge reaction of the positive electrode in nickel-cadmium cells. Early work in the field has been reviewed [9], No significant new work has been reported in recent years. 

Oxidation of organic substrates with molecular oxygen on nickel complexes is limited to a few known examples. 

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. 

Figure 3. Adsorption of carbon monoxide on nickel oxide containing preadsorbed oxygen...

An example of a different kind is afforded by the catalytic oxidation of CO on nickel oxide. Oxygen is taken up by the NiO to form a deficit semi-conductor the addition of an oxygen atom to an anion lattice site creates an adjacent vacancy in the cation lattice and draws electrons from the valence band of the lattice to produce an 0 ion. The cation vacancy traps a positive hole in its field and can move through the immediate sub-surface layers of the lattice by a vacancy mechanism. 

At room temperature, carbon monoxide is adsorbed on nickel oxide [NiO(200°)J to a larger extent than oxygen. At a maximum pressure of 30 torr, 14.08 cm of carbon monoxide is adsorbed per gram of oxide (0 = 0.24) compared to 3.67 cm of oxygen (0 = 0.12) (23). During the adsorption, there is no modification of the electrical conductivity of the... 

The spectrum of carbon monoxide adsorbed on nickel oxide prepared at 200° may be divided into two regions (Table I, la) (60). The first includes two bands at 2060 and 1960-1970 cm i, the second three bands at 1620, 1575, and 1420-1440 cm-i. Bands at 2060 and 1960-1970 cm- are typical of carbonyl structures and are found in the spectrum of carbon monoxide on metallic nickel (61). It has been suggested by some authors (62) that, in our experiments, these bands were also produced by the adsorption on the metal, the oxide being supposed oxygen-deficient. Chemical analyses (30) have shown, however, that, NiO(200°) contains an excess of oxygen and magnetic susceptibility measurements (33) have demonstrated that the quantity of metal is very small. Since the intensity of these bands is strong, we believe that they are not produced exclusively by the chemisorption of carbon monoxide on the metal but mainly by the adsorption on exposed nickel ions. 

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