Oxygen on nickel

This apparatus has been used in a number of investigations, and others are in progress. All of these are basically quite simple. In fact, they have been purposely designed to be as simple as possible. 

It has seemed to us that the first set of investigations must necessarily be concerned with a clean crystal surface, and the second set with atoms or molecules of a single gas upon a clean surface. Only after these have proved successful can one hope to study two gases on a surface. It is possible that the most important applications of this new technique will be in the field of catalysis and will involve gases of two sorts. We have the intention of carrying out such more complex studies, but have not yet got around to them. The purpose of this paper is to bring the possibilities of the experi- 

A typical diffraction pattern from the clean crystal is reproduced in Fig. 3. The fourfold symmetry of this pattern, corresponding to the symmetry of the surface nickel atoms as shown in Fig. 4, is evident in the photograph. I he azimuth of the diffraction spots of Fig. 3 is designated A. 

As the voltage of the primary electron beam is varied continuously from 0 to 500, diffraction beams appear alternately in the two principal azimuths, A and B in Fig. 4. Each beam reaches a maximum intensity at a particular voltage and these voltages represent electron wavelengths appropriate to Laue diffraction beams from the crystal. All of the diffraction beams correspond, within the experimental errors of the measurements, to a crystal 

To study the adsorption of oxygen, the gas is admitted through a Granville-Phillips valve to give a low controlled pressure. The total exposure to oxygen is appropriately measured by the product of the gas pressure and the exposure time. A convenient unit of exposure is 10 mm. Hg sec. which would be about the exposure required to cover the crystal surface with a monolayer if every molecule which collided with the surface were to stick to it. 

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Fig. X. Hydrogen adsorption at 78° and 300°K as a function of preadsorbed amount 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)-... 

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

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.

I. Panas, P. Siegbahn and U. Wahlgren (1987), Model Studies of the Chemisorption of Hydrogen and Oxygen on Nickel Surfaces. I. The Design of a One Electron Effective Core Potential Which Includes 3d Relaxation Effects , Chem.Phys. 112, 325... 

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... 

HONever, experiments have shown no significant influence of the HjO/Hj ratio. This result may appear surprising in view of the high heat of chemisorption of oxygen on nickel (ca.430 kJ/mol 0-]. But this value is less than the heat of chemisorption for sulfur, (ca. 520 kJ/mol Sj, Table 1). These values... 

Consider the temperature. It is certainly known widely that heating in the presence of a corrosive gas produces bulk compounds on a surface, yet the critical temperature of surface compound formation is poorly known. Experiments of Mitchell and Allen (363) demonstrated that an oxide film 25 A thick forms by exposure of an evaporated copper film to oxygen at room temperature. When the temperature was lowered to — 183°C, however, only a monolayer was obtained. Evidently an oxidation temperature lies between these extremes. The experiments of Brennan and Graham (359) gave similar results for oxygen on nickel, and Koberts and Wells (364) have recently shown that oxygen penetrates aluminum films at — 195°C. 

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... 

The mean-square displacement of surface atoms should be sensitive to changes in the number and type of neighboring atoms. The adsorption on the clean surface of gases that chemically interact with the surface atoms (e.g., oxygen on nickel or tungsten) strongly affects the vibrational amplitude of surface atoms. 

Panas I, Siegbahn P, Wahlgren U (1987) Model studies of the chemisorption of hydrogen and oxygen on nickel surfaces. I. The design of a one-electron effective core potential which includes 3d relaxation effects. Chem Phys 112 325-337... 

King WJ, Tseung ACC. The reduction of oxygen on nickel-cobalt oxides H correlation between crystal structure and activity of Co2NiO and related oxides. Electrochim Acta 1974 19 493-8. 

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. 

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