Catalysts oxygen adsorption

M.V. Badani, and M.A. Vannice, Effects of cesium and chlorine on oxygen adsorption on promoted Ag/a AI203 catalysts, Appl. Catal. A 204, 129-142 (2000). 

Ruthenium/carbon catalysts have also been promoted by the addition of Fe. Bron et al. reported the addition of Fe to a preformed Ru/C catalyst via adsorption of Fe complexes, followed by heat treatment. They found an increase in oxygen reduction activity of three to five times over unmodified Ru/C. It was suggested that the surfaces of Ru particles were covered with FeN,Cy sites. As discussed previously, the Pd alloys have shown significant MeOH tolerance toward oxygen reduction and appear to have activities closest to that of Ft. 

As alluded to before, the adsorption of atoms and molecules may also induce segregation in alloys. Upon revisiting the thermodynamic behavior of the improved Cu-Ag alloy catalysts for ethylene epoxidation synthesized by Linic et al, (section 2.1) Piccinin et al. calculated that, while in the absence of oxygen Cu prefers to stay in the subsurface layers, oxygen adsorption causes it to segregate to the surface which then phase-separates into clean Ag(lll) and various Cu surface oxides under typical industrial conditions (Fig. 7). This casts doubt on the active state of the previous Cu-Ag catalysts being a well-mixed surface Ag-Cu alloy. 

Vayenas and co-workers31,32 used cyclic voltammetry to investigate oxygen adsorption and ethylene oxidation over a Pt catalyst-electrode. A cathodic... 

On metal surfaces, well-ordered structures are often formed [7, 79-82], At sufficiently high temperatures (> 300 K) and pressures (> 10 6 Torr), oxygen diffuses into the catalyst bulk [8, 61, 73 76, 83-91] in Pd, as many as 300 monolayers are dissolved [83] whereas in Ir and Pt the number of dissolved monolayers is slightly lower [78, 85 87]. The oxygen dissolved in the subsurface layer changes the reaction rate constants considerably (see Table 3 [86]). Finally, under certain conditions, oxygen adsorption can lead to surface reconstruction [7, 92]. Various types of oxygen adsorption over Pt metals have been studied in detail by Savchenko [7]. 

An ideal SC-SOFC has the same OCV and I-V output as a double-chamber cell, given a uniform oxygen partial pressure. A difference in catalytic properties of the electrodes must be sufficient to cause a substantial difference in oxygen partial pressure between the electrodes. For the ideal SC-SOFC, one electrode would be reversible toward oxygen adsorption and inert to fuel, while the other electrode would be reversible toward fuel adsorption and completely inert to oxygen [30], Advances in electrode catalyst materials are needed for SC-SOFC to have the same performance as conventional double-chamber SOFC with a significant reduction in complexity and cost. 

Ohta and Tezuka (5) studied the reaction in the pressure range 0.8 - 2.4 MN/m2 and temperatures of 423 K. They found that the oxygen adsorption rate was proportional to the partial pressure of oxygen and increased rapidly with increase in temperature. The rate of oxidation was not affected by the presence of cobalt and manganese salts, but the length of the induction period was a function of these catalysts. 

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