Competitive chemisorption

When other gases are present in the gas phase in addition to 02, then I0 can be affected in two different ways First because 0o may be affected due to a catalytic reaction and/or due to competitive chemisorption. Second because these gases may react with O2 at the tpb. In general it is difficult to determine experimentally which one of these two factors is more important. 

Chemisorption Adsorbate Orientation Competitive Chemisorption Adsorbate Exchange Adsorbate Reactivity Electrocatalvsis Synthesis Mode of Coordination Ligand Substitution Ligand Exchange Ligand Reactivity Homoqeneous Catalysis... 

The ion-water interactions are very strong Coulomb forces. As the hydrated ion approaches the solution/metal interface, the ion could be adsorbed on the metal surface. This adsorption may be accompanied by a partial loss of coordination shell water molecules, or the ion could keep its coordination shell upon adsorption. The behavior will be determined by the competition between the ion-water interactions and the ion-metal interactions. In some cases, a partial eharge transfer between the ion and the metal results in a strong bond, and we term this process chemisorption, in contrast to physisorption, which is much weaker and does not result in substantial modification of the ion s electronic structure. In some cases, one of the coordination shell molecules may be an adsorbed water molecule. hi this case, the ion does not lose part of the coordination shell, but some reorganization of the coordination shell molecules may occur in order to satisfy the constraint imposed by the metal surface, especially when it is charged. 

The assumption of reactive chemisorption may be useful for the surface intermediate of C5 cyclic reactions. It may well be possible that a competition occurs between a reactive and a dissociative chemisorption the former giving C5 the latter cyclic products. There is a thermodynamic relationship between these two surface species (see Section II,A,2). Scheme XIII summarizes all the above-mentioned facts about hydrogen effects and various surface intermediates (31). 

While the rate of cleavage is given by temperature, acidity of the catalyst and concentration of i-alkyl cations, the rate of desorption is assumed to be enhanced by the steady state concentrations of n-alkenes, i. e., a high dehydrogenation activity of the catalyst favors hydroisomerization. This is the concept of competitive chemisorption which in ideal bifunctional catalysis keeps the residence times of the alkylcarbenium ions low. 

This is consistent with a most effective role of competitive chemisorption in ideal hydrocracking which minimizes the amount of secondary isomerization. 

The higher contents of branched isomers found in the fraction p = m-1 as compared to the fraction p = m-2 are best explained by the second route Secondary hydroisomerization of n-C H2 + 2 is exPected to be faster for p = m-1 due to both higher reactivity (cf. Figure 3) and competitive chemisorption. 

Fig. 13. Competition of benzene with cumene for chemisorption on active sites. The rate of cracking as a function of partial pressure of pure cumene is given by the solid curve. The rate of cracking of cumene diluted with 51 mole per cent benzene is given by the circle.

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