Desorption slow oxygen

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. 

The mixed-conducting membrane eliminates the cryogenic air separation plant and it forms a safety barrier between the natural gas and air. The membrane becomes more productive in a configuration like this, because the slow oxygen desorption at the permeate side is enhanced by the chemical reaction. 

As in the carbon-carbon dioxide reaction, mechanisms A and B can be treated for the cases where either the surface rearrangement or desorption of the carbon-oxygen complex is the slow step. This has no effect on the discussion except that the significance of the rate constant js in Equation (10) is altered, as previously discussed. 

In the experiment with 1 hour of oxygen pretreatment, all 0 and some Oco must have been generated. Upon introducing CO, it would at first react with 0 o to form some adsorbed carbonate species. The subsequent desorption of C02 must be faster than its formation. This would explain the rapid rise and slow decline of the CO2 response. As CO2 keeps forming, the number of Oco will decline and ultimately vanish. After that, CO would react with strongly bound 0 to create vacancies,... 

In this model, the first step is the dissociation of C02 at a carbon free active site (Cfas), releasing CO and forming an oxidized surface complex [C(O)]. In the second step, the carbon-oxygen complex subsequently produces CO and a new free active site. The reverse reaction is relatively slow compared with the forward reaction, so the second reaction can be treated as an irreversible reaction. In this model, desorption of the carbon-oxygen surface complex is the rate-limiting step. The rate for this mechanism can be described by the Lang-muir-Hinshelwood rate equation. Furthermore, the C/C02 reaction rate is dependent on the CO and C02 partial pressures and is inhibited by the presence of carbon monoxide. A widely utilized reaction rate equation based on this mechanism is... 

Menzel and Corner 147) observed desorption of gases from a tungsten field-emitter tip under slow-electron bombardment. They note that the process is in general inefficient, with a cross section about 10 of that for ionization or excitation in the gas phase. This desorption under bombardment with slow electrons was used by Zingerman and Ishchuk 148) as an analytical technique in a study of adsorption of oxygen on tungsten. Desorption by electron bombardment from copper and stainless steel was reported by Auslender and Minchenkov 148a). 

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