Unimolecular reactions surface-catalyzed

Consider a surface-catalyzed unimolecular reaction A, — Bg with A and B gases with partial pressures Pas and Pbs above the catalytic surface and coverages 6a and 6b on the surface. The elementary steps and their rates for a simple unimolecular reaction might be... 

The chemical reaction step is normally composed of various steps, and a broad diversity of rate laws and reaction mechanisms are relevant for surface-catalyzed reactions. However, if the simple assumption that the chemical reaction consists of a sole unimolecular or bimolecular elementary reaction or a rate determining simple reaction followed by one or more fast steps, is made, then the reaction kinetics can be mathematically treated [92],... 

In (5.60a) adsorbate undergoes a unimolecular transformation an example is the formation of atomic H at the walls of a high-temperature reaction vessel containing H2. In (5.60b) adsorbate reacts with a gas molecule as is found in some surface-catalyzed combinations of atoms and free radicals.In (5.60c) adsorbed molecules on neighboring sites interact, as seems to be the case in the exchange reaction between Dg and Corresponding to the mechanisms are the rate equations... 

A spherical non-porous particle of radius R is considered, on the external surface of which a unimolecular first order irreversible chemical reaction is taking place catalyzed by the surface of the pellet. The solid particle has a finite thermal conductivity and is immersed in an infinite medium. 

Kinetic treatments are relatively simple for spontaneous reactions, both unimolecular and bimolecular water-catalyzed reactions, because only the transfer equilibrium of the substrate between solvent and the association colloid has to be considered, Eq. (3). For example, the rate of decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion (3) is a useful indicator of medium polarity, and reaction is inhibited by solvents that hydrogen bond to the carboxylate moiety [96]. The reaction is accelerated by a variety of colloidal species that incorporate 3. including ionic and zwitterionic micelles [97,98] and O/W microemulsions [99]. Reactions are slightly slower in microemulsions derived from cetyltrimethylammonium bromide (CTABr) than in the corresponding aqueous micelles, but changes in the alcohol cosurfactant or the hydrocarbon, or in their relative concentrations, do not have major rate effects, and it appears that these microemulsion droplets are similar to aqueous micelles as submicroscopic reaction media. These observations are consistent with estimates of surface polarities [99-101] determined with bound fluorescent probes [102]. 

---