Bridge-adsorption

Numerous adsorption complexes of CO and AN in Na-A and in Na-FER were investigated only some of these adsorption complexes (giving an example of each type) are summarized in Table 1. First we discuss the effect from the top due to the interaction with the secondary cation(s). The CO molecule adsorbs on the primary cation (via C end) and when the secondary extra-framework cation is at a suitable distance from the primary cation CO forms a bridged adsorption complex between the... 

On-top geometry (t) ) and a mixture of on-top and bent-bridged adsorption modes ... 

Figure 1.9. The local aligned-bridge adsorption sites of the formate (HCOO-) species on Cu(110) and Cu(100). Also shown is the cross-bridge site on Cu(100) originally proposed as a new type of surface bond but subsequently shown to be incorrect.

In a considerable number of cases both sets of modes have been observed in on-specular VEEL spectra, and the deduction has been made that the symmetry of the surface complex is Cs (or less) (145,146,151,152,160,162). The question remains whether this implies a twofold bridged adsorption site or a neighbor-induced asymmetry within an essentially C3 site, as already described. However, there are examples of species on Pt(lll) (150), Ni(ll 1) (117), and Cu(lll) (161) surfaces for which MSSR as applied to VEEL spectra clearly indicates C3v symmetry of the surface complex, without significant differences in the other frequencies as observed off-specular. These favorable cases may arise from particularly regular arrays of adsorbed species, the presence of which could very profitably be confirmed by LEED. We deduce that the CH3 adsorption sites are intrinsically C3v as far as the bare surface is concerned, i.e., on-top or threefold hollow in nature with the threefold axis of the CH3 group perpendicular to the surface. 

Table 1 summarizes the main types of structures that are formed upon adsorption of C2H2 on some of the most extensively studied transition metal surfaces. As Table 1 shows the adsorption mode of acetylene depends on the electronic structure of the surface. For example on (111) surfaces, the p-bridging adsorption mode (II on Fig. 

Scheme 6. Reaction pathways for the ORR in acid medium for three different adsorption modes, the Griffith adsorption model (pathway 1), the Pauling adsorption model (pathway 2) and a bridged adsorption model (pathway 3).

The adsorption of carboxylic acids (CAs) on the Zn-ZnO(OOOl) surface was studied by DFT calculations including dispersion forces (DFT + D) [80]. Carboxylic acids of formula CH3(CH2) -2C00H (where n = 1-10 is the total number of C atoms in the CA) were considered. Comparing different possible adsorption modes, it was concluded that the most likely mechanism for CA adsorption on the Zn-ZnO(OOOl) surface is dissociative bridging adsorption with the carboxylate group attached to 2 Zn atoms and the proton transferred to the neighboring Zn atom, forming a Zn-H bond. 

On Ir, Rh, and Co the depletion of the d valence-electron band enhances the local density of states of the d electrons at the Fermi level, and it appears that the interaction with the doubly occupied a orbitals may become attractive. Whereas on the Ni surface backdonation into the In orbitals is favored over a donation and, as a consequence, bridge adsorption is favored, on Co the increased interaction with the d valence electrons enhances the In backdonation in the atop position with respect to the bridge position, changing the balance to the atop position. The same happens on Rh compared to Pd. 

CO oxidation to CO2 involves 2 electrons. If one CO molecule occupies one Pt atom in a linear adsorption configuration (Pt-COad), the ECSA would be calculated by dividing the integrated CO oxidation charge area by 0.42 mC cm Pt. If one CO molecules occupies two Pt atoms in a bridge adsorption configuration (2Pt-COad),... 

The formation of dimetal face-to-face macrocycles can effectively promote a 4-electron transfer pathway from oxygen to water. For example, such catalysts include dicobalt face-to-face porphyrins [15], and pillared dicobalt cofacial porphyrins [16], as well as other binuclear and polynuclear Co phthalocyanines [17]. In this catalyst, two Co centers can provide two adsorption sites for O2 to form a bridge adsorption, facilitating a 4-electron transfer process, as suggested by Anson et al. [18, 19] ... 

Figure 9.6. Interactions platinum-oxygen in the case of Griffith and Bridge adsorption models.

Fig. 30 Optimized adsorbed structures of black dye cm the Ti02 anatase (101) surface. Protonated adsorptiMis with one and two protonated anchors are labeled as plx and p2x, respectively (x = a,b), while dlx and d2x (x = a,b) indicate the structures with deprotonated one and two anchors, respeaively. blx (x = a,b) indicates the bidentate bridging adsorptions with one anchor. Reprinted with permissitm of [114]. Copyright (2012) American chemical Society...

However, a bridge adsorption configuration (2Pt-COad) may happen if one CO molecule occupies two Ft atoms. In that case, a charge required to oxidize a monolayer CO adsorbed on Ft is equal to 210 xC/cm. Those two CO adsorption configurations are strongly influenced by the applied potential. A linear adsorption may dominate if the CO adsorption occurs at a potential close to OV, as shown in a recent study [163]. 

Zitha, P.L.J. 2001. In-Depth Filtration of Macromolecules Induced by Bridging Adsorption in Porous Media. Paper SPE 68980 presented at the SPE European Formation Damage Conference, The Hague, 21-22 May. DPI 10.2118/68980-MS. 

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