Gallium oxygen adsorbed

Thermochemical Cycles Testing the Formation of Gaseous (Cycle 1) or Adsorbed (Cycle 2) Carbon Dioxide by the Interaction of Carbon Monoxide with Oxygen Preadsorbed on Gallium-Doped Nickel Oxide ... 

Removal of lattice oxygen from the surface of nickel oxide in vcumo at 250° or incorporation of gallium ions at the same temperature [Eq. (14)] causes the reduction of surface nickel ions into metal atoms. Nucleation of nickel crystallites leaves cationic vacancies in the surface layer of the oxide lattice. The existence of these metal crystallites was demonstrated by magnetic susceptibility measurements (33). Cationic vacancies should thus exist on the surface of all samples prepared in vacuo at 250°. However, since incorporation of lithium ions at 250° creates anionic vacancies, the probability of formation of vacancy pairs (anion and cation) increases and consequently, the number of free cationic vacancies should be low on the surface of lithiated nickel oxides. Carbon monoxide is liable to be adsorbed at room temperature on cationic vacancies and the differences in the chemisorption of this gas are related to the different number of isolated cationic vacancies on the surface of the different samples. 

Chemisorption of carbon dioxide on doped oxides prepared at 250° was also studied calorimetrically. Initial heats of adsorption on NiO(10 Li)(250°) (27 kcal/mole) and on Ni0(10 Ga)(250°) (28 kcal/mole) are similar. The gallium-doped oxide chemisorbs at room temperature the same quantity of carbon dioxide (9.3 cm /gm) as NiO(250°) (9.7 cm3/gm), whereas the quantity of gas adsorbed on Ni0(10 Li)(250°) is larger (13.0 cm /gm). Lithia chemisorbs carbon dioxide at room temperature. However, the difference between the quantities of gas adsorbed on pure and lithiated oxides is not explained by the presence of lithia, as a separate phase, in the doped sample. It seems, therefore, that carbon dioxide, as oxygen, is chemisorbed at room temperature on anionic vacancies whose concentration is particularly large on lithiated oxides. 

Adsorption of carbon monoxide on a gallium-doped sample [NiO(10 Ga)(250°)] precovered by oxygen decreases the electrical conductivity of the solid, whose color changes from black to green. Carbon dioxide is therefore formed. It appears from cycles 1 and 2 (Table XIII) that the interaction product remains adsorbed on the most active surface sites (6 = 0) and is desorbed from less active sites (6 = J0m)-Carbon dioxide is indeed found in the cold trap (1 cm /gm). Since cycle 3 (Table XIV) is balanced neither for 0 = 0 nor for 0 = 0m, the intermediate formation of C03-(ads) is precluded. 

The calorimetric study of interactions on the surface of gallium-doped nickel oxide therefore yields results which are similar to those obtained on pure Ni0(250°), although the incorporation of trivalent ions changes somewhat the surface affinity toward oxygen. In both cases, two reaction mechanisms for the production of gaseous carbon dioxide are probable. In mechanism II, a reaction intermediate, C03-(ads) is formed whereas, in mechanism I, gaseous carbon dioxide is produced directly by the interaction of carbon monoxide with adsorbed... 

---