Chemisorption single-adsorption

The interaction energy, AIT, is the contribution (positive or negative) to AE, due to the (indirect) interaction between the two adatoms. In other words, AIT is the difference between the chemisorption energy AE for the doubleadsorption system and the sum of the chemisorption energies A (A = a or b) for the two individual single-adsorption systems, i.e.,... 

The results on the group Ib elements appear to indicate a weak initial chemisorption process producing an electropositive layer. Only on copper surfaces, where the bonding is the strongest, is there any evidence of more than a single adsorption phase. Silver is found to be far less active towards CO chemisorption than either copper or gold. 

Chemisorption Chemical adsorption occurs when a chemical bond or a partial chemical bond is formed between the surface (adsorbent) and the adsorbate, leading to the specificity of the process. In gen- eral, but not always, the formation of a bond limits the coverage to at most one chemisorbed adsorbate for every surface atom. This limit of a single layer or monolayer is exploited later to derive a statement of conservation of sites. The upper limit need not have a one-to-one adsorbate to surface atom stoichiometry for example, saturation can occur after one-third of all sites are occupied. 

Fig. XVIII-13. Activation energies of adsorption and desorption and heat of chemisorption for nitrogen on a single promoted, intensively reduced iron catalyst Q is calculated from Q = Edes - ads- (From Ref. 130.)...

Yan C, Jensen J A and Kummel A 1994 Large island formation versus single site adsorption for CI2 chemisorption onto Si(111 )-7 X 7 surfaces Phys. Rev. Lett. 72 4017-20... 

There is a very rich literature and a comprehensive book6 on the role of promoters in heterogeneous catalysis. The vast majority of studies refers to the adsorption of promoters and to the effect of promoters on the chemisorptive state of coadsorbed species on well characterized single crystal surfaces. A... 

In case of the charged form of chemisorption a free lattice electron and chemisorbed particles get bound by exchange interaction resulting in localization of a free electron (or a hole) on the surface energy layer of adparticles which results in creation of a strong bond. Therefore, in case of adsorption of single valence atom the strong bond is formed by two electrons the valence electron of the atom and the free lattice electron. 

There is a wealth of information available on CO chemisorption over single-crystal and polycrystalline platinum surfaces under ultrahigh-vacuum conditions research efforts in this area have gained a significant momentum with the advent of various surface analysis techniques (e.g., 2-8). In contrast, CO chemisorption on supported platinum catalysts (e.g., 9, 10, 11) is less well understood, due primarily to the inapplicability of most surface-sensitive techniques and to the difficulties involved in characterizing supported metal surfaces. In particular, the effects of transport resistances on the rates of adsorption and desorption over supported catalysts have rarely been studied. 

The chemisorption of species occurs at specific sites on the electrode, for example on top of certain atoms, or in the bridge position between two atoms. Therefore, most adsorption studies are performed on well-defined surfaces, which means either on the surface of a liquid electrode or on a particular surface plane of a single crystal. Only fairly recently have electrochemists learned to prepare clean single crystal electrode surfaces, and much of the older work was done on mercury or on amalgams. 

Here, the first factor in square brackets represents the adsorption of a single atom at site m. The second factor represents the adsorption of a second atom at site —n. Substituting (8.52) into (8.43), and invoking the chemisorption functions (4.68), (4.69), (8.16), (8.17), along with (8.46), results in... 

The subscripts 1 and 2 on the chemisorption functions refer to single- and double-adsorption, respectively. Note, however, that eaa and ha are given by (8.2), where the indicated occupancies are both for the double-chemisorption... 

The use of CO as a chemical probe of the nature of the molecular interactions with the surface sites of metallic catalysts [6] was the first clear experimental example of the transposition to surface science and in particular to chemisorption of the concepts of coordination chemistry [1, 2, 5], In fact the Chatt-Duncanson model [7] of coordination of CO, olefins, etc. to transition metals appeared to be valid also for the interactions of such probes on metal surfaces. It could not fit with the physical approach to the surface states based on solid state band gap theory [8], which was popular at the end of 1950, but at least it was a simple model for the evidence of a localized process of chemical adsorption of molecules such as olefins, CO, H, olefins, dienes, aromatics, and so on to single metal atoms on the surfaces of metals or metal oxides [5]. 

Because chemisorption involves a chemical bond between the adsorbate and adsorbent, only a single layer of chemisorption can occur. Physical adsorption on top of the chemisorbed layer and diffusion of the chemisorbed layer beneath the surface can obscure the fact that chemisorbed material can be only one layer in depth. 

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