Nickel oxide adsorption isotherm

Fig. 8. Adsorption isotherms of CO2 on reduced nickel (T = 200°C., Ae = 22 kcal./mole), copper ferrite (T = 300°C., Ae = 31 kcal./mole), and ferric oxide (T = 300°C., Ae = 29.5 kcal./mole).

In this work, nickel oxides are prepared by dehydration under vacuum (10 torr) at moderate temperatures (200-300 ) of a pure nickel hydroxide. The hydroxide itself is prepared by the steam distillation of a solution of reagent grade Ni(NOs)2 in an excess of aqueous ammonia (22). As has been shown (22), this method yields Ni(OH)2 containing less than 0.08% of NHs and N2O6. When dried at about 60°, the product has the composition NiO, 1.05 H2O and its BET surface area amounts to 34 m /gm. The external aspect is that of a fine crystalline powder and not of a gel. There are no small-diameter pores in the hydroxide particles since the adsorption-desorption isotherm of nitrogen at —195° does not present an hysteresis loop. The X-ray diagram is that of a well-crystalized nickel hydroxide. 

Nickel Adsorption onto Silica and Goethite. Figure 4 contains adsorption isotherms for nickel onto -Si02 and a-FeOOH as compared with precipitation which occurs in the absence of oxide surfaces. The lines in Figure 4, as with all figures in this chapter showing sorptive behavior, are predicted using the James and Healy model in conjunction... 

On AI2O3 surfaces, a coexistence of several types of OH groups and water molecules has been found (Coustet and Jupille, 1994a Frederick et al, 1991b). On the reconstructed (100) face of Cu02, terminated with copper atoms, hydroxyl groups and water molecules are detected at 110 K, while only dissociative adsorption takes place at 300 K (Cox and Schulz, 1991). Thanks to adsorption isotherm measurements and infra-red absorption, hydroxyl groups have been identified on BeO(lOlO) (Miyazaki et al, 1985). On thin nickel oxide films, dissociation of water may occur on the polar 111 faces, but it depends upon the oxide thickness. 

Cutlip and Kenney (44) have observed isothermal limit cycles in the oxidation of CO over 0.5% Pt/Al203 in a gradientless reactor only in the presence of added 1-butene. Without butene there were no oscillations although regions of multiple steady states exist. Dwyer (22) has followed the surface CO infrared adsorption band and found that it was in phase with the gas-phase concentration. Kurtanjek et al. (45) have studied hydrogen oxidation over Ni and have also taken the logical step of following the surface concentration. Contact potential difference was used to follow the oxidation state of the nickel surface. Under some conditions, oscillations were observed on the surface when none were detected in the gas phase. Recently, Sheintuch (46) has made additional studies of CO oxidation over Pt foil. 

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