Desorption of oxygen

Sherwood and Holloway [61] also studied the desorption of oxygen from water. 

S. Neophytides, D. Tsiplakides, and C.G. Vayenas, Temperature-Programmed Desorption of Oxygen from Pt-films Interfaced with Y203-Doped Zr02> /. Catal. 178, 414-428 (1998). 

Campbell CT, Ertl G, Kuipers H, Segner J. 1981. A molecular beam study of the adsorption and desorption of oxygen from a Pt(lll) surface. Surf Sci 107 220-236. 

The slow desorption of oxygen will also suggest that the desorption of oxygen from the catalyst could be the slowest step during the steady state reaction. 

It will, therefore, be plausible to conclude that the decomposition of nitrous oxide on CuO is taking place predominantly through the reaction step (1) with the desorption of oxygen as the slowest step. 

The desorption of oxygen which was suggested as the slowest step on CuO catalyst is the rupture of a M-0 bond in its nature and the adsorption of nitrous oxide through oxygen end which was suggested as the slowest step on MgO catalyst is the formation of a M-0 bond. Therefore, the results we have obtained in the present study appears to be consistent to the conclusion proposed by Vijh. 

As seen in reaction (6.5.3) photogenerated holes are consumed, making electron-hole separation more effective as needed for efficient water splitting. The evolution of CO2 and O2 from reaction (6.5.6) can promote desorption of oxygen from the photocatalyst surface, inhibiting the formation of H2O through the backward reaction of H2 and O2. The desorbed CO2 dissolves in aqueous suspension, and is then converted to HCOs to complete a cycle. The mechanism is still not fully understood, with the addition of the same amount of different carbonates, see Table 6.2, showing very different results [99]. Moreover, the amount of metal deposited in the host semiconductor is also a critical factor that determines the catalytic efficiency, see Fig. 6.7. 

The presence of fine solid particles or a finely dispersed second liquid phase in the continuous absorbent phase can have a very strong effect on the mass transfer rate between the gas and the continuous phases. The mass transport into the solid particles or liquid drops can essentially alter the concentration gradient and, consequently, the absorption rate [27-36]. The qualitative explanation of this phenomenon is that the particle absorbs oxygen in the oxygen-rich hydro-dynamic mass transfer film, after which, desorption of oxygen takes place in the oxygen-poor bulk of the liquid. 

The oxygenated complex desorbed molecular oxygen on heating under reduced oxygen pressure. Desorption of oxygen, i.e. regeneration of the ferroheme complex,... 

Fritzsche (45) used a technique similar to that of Stockmann, but held the sample in a vacuum while taking measurements. His ZnO samples were prepared by evaporation in an oxygen atmosphere at about 300°C. Again, the conductivity was found to be reversible below 300°C. In these experiments, as the temperature was raised, the conductance increased monotonicly. Due to the vacuum, only a desorption of oxygen was possible in these experiments. When the temperature was lowered, still in a vacuum after reaching 460°C, the conductivity remained high, as little readsorption occurred, due to the low pressure. A time dependent rise in conductance was observed if the temperature was kept at 46O C, as observed before by Bevan and Anderson (31), and attributed to the desorption of oxygen. 

Fig. 31. Variation of the activation energy with coverage for the thermal desorption of oxygen from Ir(l 10) (124).

Equation (1) represents the physical adsorption/desorption of oxygen which has been established by direct experiment (32) to occur very rapidly at low temperatures and is not a rate-limiting process at exchange reaction temperatures. 

Adsorption-desorption of oxygen. As a rule, oxygen adsorption over Pt metals is dissociative with practically zero activation energy [12-14, 41-50, 64-76],... 

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