Adsorption reaction conceptual model

The nature of the problem in establishing a mechanistic model of the oxide-electrolyte interface, in which chemical and electrostatic energies are described explicitly, can be appreciated by consideration of the adsorption reaction depicted in Figure 2. The adsorption of a hydrogen ion from the bulk of a monovalent electrolyte is considered. The oxide-solution interface is divided conceptually into four regions the bulk oxide (not shown in the figure), the oxide surface at which the adsorption reaction takes place, the solution part of the double layer containing the counterions, and the bulk of solution. 

A conceptual model depicting the sequences of steps in this platinum-catalyzed reaction is shown in Figure 10-10. Figure lO-lOis only a schematic representation of the adsorption of cumene a more realistic model is the formation of a complex of the -it orbitals of benzene with the catalytic surface, as shown in Figure 10-11. 

Two general types of models have been developed to desaibe adsorption/desorption reactions at mineral surfaces (1) empirical models that are based on the partioning relationships of a solute between the aqueous and solid phase, and (2) conceptual models for surface... 

Consider the situation of a different metal ion, say Zn ", dissolved in a solution containing FeOOH. Just as in the cases described earlier, the zinc ion may appear as a free aquo ion, as a hydroxo- or other complex, or in the present case as a complex with the surface oxide site. The empirical evidence is that in many cases the most stable arrangement is for the Zn or other dissolved metal ion to replace hydrogen ions at the surface and hence be preferentially adsorbed (Fig. 15-4b). As would be expected, since the reaction is effectively a competition between the metal and hydrogen ions to bind to the oxide, metal ion adsorption is enhanced at high pH and diminished at low pH (Fig. 15-5a). This conceptual model for adsorption is also consistent with the observation that the adsorptive bond strength of... 

Several different approaches can be used to model the interaction of solutes with reactive mineral surfaces. The conceptual approaches differ in the degree to which they account for observed or postulated solution and surface reactions. Whatever the approach, the description of interactions at the particle/solution interface must inevitably take into account the effect of pH on solute adsorption. 

A simple tool is described, which provides a conceptual framework for analyzing microkinetic models of heterogeneous reactions. We refer to this tool as the Sabatier Analysis . The Sabatier Analysis of the microkinetic models developed in this section suggests that the clustering of good catalysts can be explained by the combination of the universal BEP-relation and activated re-adsorption of synthesis products onto the catalyst. 

IS mucn more theoretical and conceptual as it is based on physico-chemical properties and models necessary to understand the host-guest interactions which occur within a zeolite framework, i.e., the way reactions occur inside the zeolite. This involves the description of the zeolite (host) and chemical compounds (guests), as well as the characterization of the intraframework phenomena diffusion process, adsorption at specific sites, reaction mechanisms, and desorption. The aim of the consideration of the complementary theoretical knowledge is i) to interpret observations done from the retrieval and analysis of the data from the empirical knowledge base ii) to endow to the system with a detailed description of zeolite catalysis at a conceptual level, to allow the system to propose predictions and solutions for particular catalytic problem by combination of these theoretical notions. 

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