Oxygen adsorption, application

An interesting application of adsorption microcalorimetry was used by these researchers to examine changes in adsorption behavior of graphite-supported iron/rhodium bimetallic catalysts as a function of oxidation and reduction treatments. The differential heat of oxygen adsorption on the bimetallic catalysts after various treatments was compared to the values obtained for the monometallic materials to determine the relative contributions to the total adsorption. Reduction at 673 K produced an alloy whose... 

The Pd-O bond also varies with the extent of oxidation of Pd. During the methane combustion reaction, the catalyst surface is a non-equilibrium, kineti-cally controlled structure. The oxygen concentration profile in the particle results from a combination of particle reconstruction, oxygen adsorption, bulk diffusion, and oxygen removal. This concentration profile varies as a function of time, and as the oxygen content increases, the Pd-O bond strength decreases. This increase is accompanied by an increase in the specific activity. The most widely accepted reaction pathway is the Mars and van Krevelen redox mechanism, which involves lattice oxygen and uneoordinated Pd centers as active species. Inhibition by products (H2O and CO2) and impurities (SO2) is a major drawback for low temperature combustion. The effect of sulfur is particularly important for catalytic converters for NGV applications because it drastically reduces the methane combustion activity. 

Mathias, P.M., et al.. Correlation of multicomponent gas adsorption by the dual-site Langmuir model Application to nitrogen/oxygen adsorption on 5A-zeolite, Ind. Eng. Chem. Res., 35(7), 2477-2483 (1996). 

The oxygen reduction reaction at the cathode (Eq. 4) can be broken down into several steps gas-phase diffusion, oxygen adsorption and dissociation at the cathode surface, surface or bulk diffusion of oxygen atoms, and incorporation into the electrolyte [4,5]. Any of these steps can limit the rate of cathodic reaction. The reaction site distributes three dimensionally aroimd the triple-phase boimdary (TPB) of electrode, electrolyte, and gas phase, as illustrated in Figme 2. In practical applications, LSM is often used as a composite with YSZ particles to increase the electrochemical reaction site. As YSZ can make a separate ionic path, the reaction site is made three dimensionally inside the electrode layer [6]. 

According to experimental data,208,209 the SNIFTIR technique can be used to probe the electrical properties of the electrical double layer even in more concentrated solutions where cyclic voltammetry (cv), impedance, chronocoulometry, and other techniques are not applicable. Iwasita and Xia210 have used FTIR reflection-adsorption spectra to identify the potential at which the orientation of water molecules changes from hydrogen down to oxygen down. 

Figure 5.22 reveals the ability of solid state electrochemistry to create new types of adsorption on metal catalyst electrodes. Here oxygen has been supplied not from the gas phase but electrochemically, as 02 via current application for a time, denoted tj, of 1=15 pA at 673 K, i.e. at the same temperature used for gaseous O2 adsorption (Fig. 5.21). Figure 5.23 shows the effect of mixed gaseous-electrochemical adsorption. The Pt surface has been initially exposed to po2 =4x1 O 6 Torr for 1800 s (7.2 kL) followed by electrochemical O2 supply (1=15 pA) for various time periods ti shown on the figure, in order to simulate NEMCA conditions. 

Successful applications of the oxygen-modified CNFs are reported on immobilization of metal complexes ]95], incorporation of small Rh particles [96], supported Pt and Ru CNFs by adsorption and homogeneous deposition precipitation ]97, 98], Co CNFs for Fischer-Tropsch synthesis ]99], and Pt CNFs for PEM fuel cells [100]. 

Note that expressions (2.24 ) and (2.36) are applicable for equilibrium adsorption of molecular gases. Moreover, this dependence becomes valid during adsorption of oxygen too when the latter is diluted in polar liquids such as H2O, CH3OH, C4H9OH, CgHi2 etc. [59]. The results of these studies related to evaluation of possibility to detect the traces of oxygen in liquid media as well as plausible mechanisms of phenomena will be considered in detail in Chapter 4. 

Our comments on adsorption of oxygen and nitrogen atoms lead to conclusion that practically under all conditions the initial rate of variation of conductivity of zinc oxide film due to adsorption of acceptor particles discussed in this section is proportional to the concentration of particles in the space adjacent to the surface of oxide film. This is similar to the case of donor particles. This means that the following equation is applicable ... 

Most states require the capture and treatment of air stripper off-gas. Typical off-gas treatment technologies that are applicable to MTBE and other oxygenates are adsorption, thermal treatment, and biotreatment. 

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