Oxygen chemisorption on nickel

It has been shown recently that the adsorption equilibrium function (/) can be used to obtain information on the thermodynamics of chemisorption processes as they occur during a catalytic reaction 2). Thus, the free energy, enthalpy, and entropy of oxygen chemisorption on nickel, platinum, and silver surfaces were determined while these surfaces were being used for the catalytic decomposition of water. 

The only conclusions that can be drawn from our experiments concerning the role of oxygen in these interactions are (1) oxygen chemisorption is faster than the subsequent interaction, and (2) oxygen can react with hydrogen on the surface of nickel in the adsorbed layer at room temperature. 

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 studies of Garner and his co-workers in the years 1928-1939, which had established the existence of two types of carbon monoxide and hydrogen chemisorption on oxides and which identified irreversible chemisorption with incipient reduction, were followed in the immediate postwar period by an intensive study of the properties of copper oxide (12-15). The work was later extended to nickel oxide (16) and cobalt oxide (17,18). With each of these oxides it was established that carbon monoxide was capable of reacting not only with lattice oxygen, but also with adsorbed oxygen. The concept of irreversible chemisorption involving a carbonate ion and ulti-... 

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... 

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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