Surface kinetic reaction stages

A variety of models have been derived to describe the kinetics of semiconductor photocatalysis, but the most commonly used model is the Langmuir-Hinshel-wood (LH) model [77-79]. The LH model relates the rate of surface-catalyzed reactions to the surface covered by the substrate. The simplest representation of the LH model [Eq. (7)] assumes no competition with reaction by-products and is normally applied to the initial stages of photocatalysis under air- or oxygen-saturated conditions. Assuming that the surface coverage is related to initial concentration of the substrate and to the adsorption equilibrium constant, K, tire initial... 

The deactivation of bulk iron oxide during methane combustion has been studied. The observed deactivation behaviour has been explained as the result of two simultaneous deactivation mechanisms. In the initial phase of reaction both are in operation and the activity drops rapidly as a consequence of both catalyst sintering and of the depletion of lattice oxygen in the outer layers, due to a partial reduction of the catalytic surface. In later stages, catalyst deactivation is almost exclusively due to sintering imder reaction conditions. A kinetic model of deactivation is presented, together with the physicochemical characterization of fresh and partially deactivated catalysts. 

Results of kinetic studies suggest that the formation reactions of the rare-earth and actinide hydrides are similar multi-stage processess occurring with formation of adherent product layers on the metal surfaces. The reaction rate, r, is dependent on the surface area of the reacting metal, the hydrogen pressure F, and the temperature T. The value of r may be influenced by a variety of secondary parameters, including surface conditions, the process history of the metal, gas purity and the sample geometry. 

To understand the details of such surface rearrangement following displacement reactions, it is first necessary to understand as fully as possible the kinetic behavior (on a second time scale) of molecules which are undergoing these surface desorption reactions in the first adsorption layer. Information from SERS experiments allows the temporal course of the displacement reaction and additional information about structures in the adsorbed state. Therefore, to examine the question of reorientation and desorption of PNP by CPC molecules, surface Raman spectra were collected in real time at different stages of adsorption. 

The overall reaction kinetics conesponding to these stages of surface adsorption followed by reaction can be represented by die equation... 

Integrating equations (2.37) and (2.39) under assumption that in case of direct reaction of surface complex formation (Me C ) the reaction of interaction of oxygen with surface metal atoms is the limiting stage rather than formation of physadsorbed oxygen (i.e. assuming that [02( )J = const and it does not change in time) we arrive to the respective expression for kinetics of direct and inverse reactions ... 

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