Chemisorption double-adsorption

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... 

As defined in Chap. 4, the chemisorption energy is the difference between the initial and final energies of the system. Although we could use the expression (4.85) for AE, it is more convenient to work with that of App. L, with a slight modification to account for double adsorption. Specifically, we have... 

The fact of a transfer of an electron from an absorbed particle to adsorbent [25] is widely considered as a criterion to differentiate between various forms of adsorption. Yet, as it has been already mentioned in previous section, there is a neutral form of chemisorption, i.e. weak binding formed without changing the surface charge state which only affects the dipole component of the work function. On the other hand, in several cases the physical adsorption can result in electron transitions in solids. Indeed, apart from formation of a double layer, changing the work function of adsorbent [26] the formation of surface dipoles accompanying physical adsorption can bring free charge carriers to substan-... 

What was evident in 1950 was that very few surface-sensitive experimental methods had been brought to bear on the question of chemisorption and catalysis at metal surfaces. However, at this meeting, Mignolet reported data for changes in work function, also referred to as surface potential, during gas adsorption with a distinction made between Van der Waals (physical) adsorption and chemisorption. In the former the work function decreased (a positive surface potential) whereas in the latter it increased (a negative surface potential), thus providing direct evidence for the electric double layer associated with the adsorbate. 

Chemisorption of anions at the electrode interface involves dehydration of hydrated anions followed by adsorption of dehydrated anions which, then, penetrate into the compact double layer to contact the interface directly, this result is called the contact adsorption or specific adsorption. The plane of the contact adsorption of dehydrated anions is occasionally called the inner Helmholtz plane... 

Finally, the dissociation of the molecule upon adsorption may also proceed in such a manner that both dissociation products will form not strong but weak chemisorption bonds. Take, for example, the Os molecule, in which the double valence bond between the oxygen atoms may... 

We observe that the sign of A

additional potential jump on the surface of the semiconductor due to the electric double layer, which arises on the surface in adsorption and figures as one of the terms in the experimentally measured work fimction. Such an electric double layer may be the result of the polarization of the chemisorbed particles (when the dipole moments of the chemisorbed particles are directed normally to the surface). This can be the case, for example, in weak chemisorption (when the total charge of the surface remains unchanged). 

The heat curves, themselves, are informative. The kaolin-based pellet catalyst has a few more active sites then attapulgite, but its site activity decreases rapidly and to values only about 3 kcal./mole above the heat of liquefaction of the liquid at maximum coverage. Obviously, a distinction cannot be made between physical adsorption and chemisorption for some of the amine adsorbed at full coverage on the cracking catalyst. On the other hand, attapulgite has a much narrower distribution of adsorption energies, and the lowest heats are about double the heat of liquefaction of butyl amine. Therefore, it appears safe to conclude that the amount remaining after evacuation at 25° is chemisorbed. 

The equations for multistep electron transfer according to the quasiequilibrium treatment can be derived on the basis of Parsons general and rigorous treatment [47]. For simplicity, mass transport limitations, double layer effects, ohmic overpotential, and specific adsorption or chemisorption are neglected in the present formalism. 

Accessible metal fractions were determined by hydrogen chemisorption. The volumetric adsorption experiments were performed at room temperature in a conventional vacuum apparatus. Hydrogen uptake was determined using the double isotherm method, as previously reported (3). The platinum dispersion (D ) was calculated by assuming a... 

In view of the difference of a factor of 10 or more in peak delay between butene and thiophene at similar temperatures, butene adsorption was checked to see that chemisorption was in fact occurring below 200° C. Using the 50-foot propylene carbonate column, it was found that some butane was formed in spite of the H2S present down to 150° C. (without H2S butene was almost completely hydrogenated at this temperature) and both cis-trans and double bond isomerization of the butenes went to completion at temperatures below 100° C., indicating that chemisorption of butene must have occurred. It is therefore felt that extrapolation of the butene sorption results obtained to the temperature range of the desulfurization reaction (above 200° C.) should be valid. 

These methods suggested in the present form by Caunt83) rely on inhibition (retardation) effects of strong catalyst poisons on polymerization. Typical poisons potentially usable for this purpose are carbon oxides, carbonyl sulfide, carbon disulfide, acetylenes and dienes. All these substances exhibit a strong unsaturation they have either two double bonds or one triple bond. Most of the works devoted to application of the poisons to determination of active centers 10,63 83 102 1O7) confirm a complicated nature of their interaction with the catalytic systems. To determine the active centers correctly, it is necessary to recognize and — as much as practicable — suppress side processes, such as physical adsorption and chemisorption on non-propagative species, interaction with a cocatalyst, oligomerization and homopolymerization of the poison and its copolymerization with the main chain monomer. 

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