Oxygen adsorbed, reactivity

These effects are most striking on silver since it is, itself, a very unreactive surface. There is every reason to expect, however, that oxygen will behave similarly on other metals. More complex reaction behavior will, of course, be observed as the intrinsic reactivity of the metal increases. Oxygen adsorbed on platinum should show similar properties. In fact the formation of surface OH groups from HjO and 0(a) was recently reported 145). The ability of platinum itself to break C-H and C-C bonds complicates oxidation mechanisms, but future work should provide a greater understanding of the relative role of surface oxygen in oxidation catalysis. 

Yoshida et al. [356] show the presence of O" and OJ on V2Os supported by Si02. With strong reduction, it is mainly O. It was proved that reaction of 02 with propene gives rise to aldehydes (propionaldehyde, acrolein and formaldehyde) at temperatures below 150°C. Yoshida et al. [357] confirm this and find that oxygen at room temperature is mainly adsorbed as molecular oxygen, only 10% is the sum of O and 02. O" is the oxygen species reactive towards carbon monoxide, 02 is not. 

The increase of the catalytic activity in the room-temperature oxidation of carbon monoxide, which results from the increase of the temperature of preparation of NiO from 200° to 250°C., is related to the difference in the reactivity of oxygen adsorbed on both surfaces. The interaction between adsorbed oxygen and carbon monoxide has roughly the same velocity on both oxides. But on NiO (200) this interaction yields only C02(ads)> whereas on NiO(250) the same interaction produces C03"(ads) on the most active sites (anionic vacancies) and C02(g) on the less... 

Apart from kinetic measurements, the studies of oxygen adsorption on silver (63, 64), electron work function variations accompanying oxygen adsorption (65-67), heat effects of adsorption (65), reactivity of oxygen adsorbed on silver (67), and oxygen isotopic exchange on silver (56-55) were used for the elucidation of the mechanism of the reaction. The papers cited contain references to the works of other authors that were used for the formulation of the reaction mechanism on a level with our results. Here we shall mention, first of all, the work by Twigg (69), who has ascertained... 

Since the oxygen adsorbed on an oxide surface is more reactive than the lattice oxygen of an n-type oxide, p-type oxides are generally less selective in their reactions than are the n-type species. Oxidation of hydrocarbons over p-type... 

Oxygen dissolved in the Ir can be identified it is unreactive towards CO or H2 even at 1100 K. Oxygen adsorbed on Ir is highly reactive to CO. Warming a surface which had NO adsorbed upon it at 170 K to 323 and 373 K resulted in loss of NO signal presumably due to NO dissociation. Adsorbed oxygen can block sites which would otherwise catalyse NO decomposition. 

Muzykantov, V.S., Popovsky, V.V., Boreskov, G.K. (1969) Reactivity of oxygen adsorbed on oxide surface 2. Isotopic exchange of oxygen in Fe-Sb-O catalysts. Kinet. Catal, 10, 1270-1277 (in Russian). 

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