Carbon monoxide interaction with preadsorbed oxygen

The same sequence of adsorptions (O2-CO) was also studied on the surface of NiO(250°) [41). As in the case of NiO(200°), adsorption of carbon monoxide on the sample containing preadsorbed oxygen (1.90 cm /gm) (Table II) changes the color of the sample from black to green and decreases its electrical conductivity (1.8 x 10- ohm-i cm- ) to the low initial value. However, this time, carbon dioxide is found in the cold trap placed near the sample. Calorimetric results reported in Table II indicate also that carbon monoxide interacts with preadsorbed oxygen since the heats of adsorption of carbon monoxide are higher on the black sample (Table II) than on the pure surface of NiO(250°) (Fig. 12). 

A. Interaction of Carbon Monoxide with Preadsorbed Oxygen... 197... 

ThermochemiccU Cydea Testing the Formation of Adsorbed Cycle 1) or Gaseous Cycle 2) Carbon Dioxide by the Interaction of Carbon Monoxide with Preadsorbed Oxygen... 

On the other hand, the mechanism of the interaction of carbon monoxide with preadsorbed oxygen appears to be closely related to the strength of the bond between the oxygen ion and the surface site. When... 

Fig. 26. Differential heats of interaction of carbon monoxide at 30°C with a sample of gallium-doped nickel oxide, containing a limited amount (0.4 cm3 02 gm l) of preadsorbed oxygen.

Fig. 29. Differential heats of interaction of carbon monoxide, at 200°C, with samples of nickel oxide containing excess oxygen, preadsorbed rapidly (A) or slowly (B).

B. Interaction of Oxygen with Preadsorbed Carbon Monoxide... 202... 

The reverse interaction, between preadsorbed carbon dioxide and oxygen from the gas phase, was also studied (66). A small quantity of oxygen can be adsorbed (1.08 cra /gm) and the electrical conductivity of the sample increases. The initial heat of adsorption (83 kcal/mole) shows that oxygen reacts with adsorbed carbon dioxide. A subsequent adsorption of carbon monoxide is again possible (1.05 cm /gm) which produces a decrease of the electrical conductivity of the sample. These results were explained, from the calorimetric data, by the formation of a small number of C03"(ads) ions by the interaction of oxygen with preadsorbed carbon dioxide. These complex ions are then converted by carbon monoxide into carbon dioxide which remains adsorbed on the oxide surface. From these experiments it was concluded (66) that, although a small quantity of preadsorbed carbon dioxide may react with oxygen, this interaction is not a possible step of the reaction mechanism and that, consequently, adsorbed carbon dioxide is an inhibitor of the catalytic process. 

Fio. 36. Differential heata of interaction of carbon monoxide at 200° with NiO(200°) containing preadsorbed oxygen. 

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