Adsorption oxidative

Wu M-C, Estrada C A, Corneille J S and Goodman D W 1996 Model surface studies of metal oxides adsorption of water and methanol on ultrathin MgO films on Mo(IOO) J. Chem. Phys. 96 3892... 

Citrate process Copper oxide adsorption Caustic scrubbing... 

S.W. Jorgensen, N.D.S. Canning, and R.J. Madix, A HREELS, TPD study of nitric oxide adsorption, desorption and reaction on clean and sulfur covered palladium (100), Surf. Sci. 179, 322-350 (1987). 

In most cases, the adatom deposition is reductive, as sketched in (7.1), because the adatom precursor in the solution is in an oxidized state. However, oxidative adsorption... 

Besides the experimental data mentioned above, the kinetic dependencies of oxide adsorption of various metals are also of great interest. These dependencies have been evaluated on the basis of the variation of sensitive element (film of zinc oxide) conductivity using tiie sensor method. The deduced dependencies and their experimental verification proved that for small occupation of the film surface by metal atoms the Boltzman statistics can be used to perform calculations concerning conductivity electrons of semiconductors, disregarding the surface charge effect as well as the effect of aggregation of adsorbed atoms in theoretical description of adsorption and ionization of adsorbed metal atoms. Considering the equilibrium vapour method, the study [32] shows that... 

Based on the collation of the theoretical and experimental results, two distinct NO activation pathways can then be proposed. The oxidative adsorption, giving rise to the bound NO8 species, defines a nitroside pathway of activation, while the reductive adsorption leading to NOs+ species is tantamount with a nitrosonium pathway of activation (Figure 2.17). 

In contrast, for the NO8- species the N—O bond is elongated, only slightly polarized, and the stretching frequency, vNO, decreases below 1850 cm-1. Such changes indicate that the activation consists in redistribution of the electron and spin densities within the M—NO unit, which accumulates on the nitrogen atom. Among the first series TMI, the oxidative adsorption is less common and includes only the tj1 CuNO] 11 and 171 3CrNO 6 adducts. The mechanistic implications of the electronic structures for both type of the nitrosyl complexes are discussed in the next section. 

Thirunavukkarasu, K., Thirumoorthy, K., Libuda, J. et al. (2005) Isothermal kinetic study of nitric oxide adsorption and decomposition on Pd(lll) surfaces Molecular beam experiments , J. Phys. Chem. B, 109, 13283. 

While thick oxide formation on Ru occurs together with Oz evolution at a potential of 1.15 Vsce, the initial steps of oxide formation are expected to occur at more cathodic potentials of roughly 0.3 0.8 V [72]. Structures in the cyclic voltammogram in this potential region were attributed by Vucovik et al. [73] to hydroxide or oxide adsorption. These oxides are reversibly reduced at a potential of 0.1 V. The presence of a thin oxide layer on Ru at potentials cathodic of 1.15 V was demonstrated by... 

The energy of nitrous oxide adsorption is defined as the energy difference between (a) and (b)... 

This model was fitted to the data of all three temperature levels, 375, 400, and 425°C, simultaneously using nonlinear least squares. The parameters were required to be exponentially dependent upon temperature. Part of the results of this analysis (K6) are reported in Fig. 6. Note the positive temperature coefficient of this nitric oxide adsorption constant, indicating an endothermic adsorption. Such behavior appears physically unrealistic if NO is not dissociated and if the confidence interval on this slope is relatively small. Ayen and Peters rejected this model also. 

Figure 5.11 Desorption of a SAM of dodecanethiolate from a rotating Cu-disk electrode, (a) Current measured at the Cu electrode, (b) Current measured at a Au-ring electrode indicating oxidative adsorption of a thiol. Electrolyte 0.1 NaOH + H2O (5%) in methanol. Reproduced with permission from Ref [165].

Silica from zeolite migrates less readily. In the magnesia-alumina system, spinel, as identified by X-ray diffraction, is inactive for SO2 removal. The effect of temperature on steam stability, oxidative adsorption and reductive desorption of SO2 are described. Five commercial catalyst types are ranked for SOx removal. 

The oxidative adsorption of SO, as shown in Equation 2, can be enhanced by using an oxidation promotor. If metal sulfide, MS, instead of metal oxide forms from the reduction of the sulfate, the sulfide must hydrolyze to MO by the action of steam in the stripper section of the ECC unit ... 

Platinum. Other materials are effective promotors for the oxidative adsorption of SO2. Figure 6, for instance, demonstrates the effect of platinum which is the best promotor and the earliest one used for the UltraCat process (31). The figure, which compares SO2 removal curves for alumina alone and with 2 and 100 ppm Pt at 1200, 1300 and 1400 F, indicates that alumina promoted with platinum at both levels is more efficient for removing SO2 than pure alumina. The catalytic effect of platinum, not unexpectedly, becomes less pronounced as the temperature is increased as can be seen by inspecting the curves and also by comparing the percentage of SO2 removed after 100 minutes as shown on Table IV. 

Without platinum, alumina becomes more effective for removing SO2 as the temperature is increased. In this unpromoted case, the rate of oxidative adsorption of SO2 controls the amount of SO2 removed. Increasing the temperature increases that rate. 

In contrast, with platinum, SO2 removal, while always greater than the unpromoted case, tends to decrease with increasing temperature. The presence of platinum increases the rate of oxidative adsorption of SO2 to the point that the capacity of alumina becomes the limiting factor rather than the rate. The capacity, limited by thermodynamics, decreases with increasing temperature because of the stability of surface sulfate species... 

Oxidative Adsorption of Sp2 Oxidative adsorption of SO2 is also a strong function of temperature as shown on Figure 15. Plotted is the amount of SO2 removed after 92 minutes from room temperature to 1500 F. The material used for these experiments was a rare earth stabilized Rhone-Poulenc alumina which was tested without dilution with cracking catalyst. A fresh charge of alumina was used at each temperature. 

Rare earths have also been included as desirable SOx catalyst components in early patents but the catalytic behavior of cerium, in particular, had not been clarified. This paper has presented evidence that cerium catalyzes the oxidative adsorption of SO2 on high alumina cracking catalyst, alumina, and magnesia. We also have shown the catalytic character of platinum. The details of the catalysis especially by cerium, however, remain unexplained. 

The measurement of the charge involved in the reductive desorption of layers prepared under various conditions provides very important information about the surface coverage and the nature of the oxidative adsorption. The influence of time and thiol concentration on both the potential and the charge of the reductive desorption has been investigated for decanethiol adsorbed on Au(lll) [125] (see Fig. 8). 

Fig. 7. Energy-minimized structures of acetone and mesityl oxide adsorption complexes on a cluster model of HZSM-5 using DFT calculation. Note that in the case of the acetone complex, the proton remains bonded to the bridging oxygen, while in the case of the mesityl oxide complex, the proton is more fully transferred to the ketone. (Reprinted with permission from Haw et al. (7). Copyright 1996 American Chemical Society.)...

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