Adsorption of Oxygen and Oxidation Catalysis on Nickel Oxide

Adsorption of Oxygen and Oxidation Catalysis ON Nickel Oxide 

As before, however, this oxidation process need not stop at this surface stage. Indeed, nickel oxide, as can many other oxides of transition metals, can accommodate a stoichiometric excess of oxygen in the bulk crystal (33). While the amount of this excess is not particularly large as compared 

1 X 10 g. at. of oxygen/g. of oxide can be readily obtained. By this method Krauss measured the rate of oxygen uptake by nickel oxide (35) and a number of other oxides (36) at 300°C., as well as the amount of oxygen taken up at that temperature after 2 hr., when apparent saturation is reached. For the rate he found a parabolic law  

however, the melting point of nickel oxide is about 2600°K., its Tammann temperature should lie around 1000°C., and it is hard to believe that ionic motion could be so rapid at 300°C. as to reach equilibrium throughout the crystal in so short a time. A more recent investigation by Engell and Hauffe (37) confirms this impression. 

After this fast process there follows a smaller slow uptake increasing with temperature and insensitive to pressure. Thus the amount taken 

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

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