Adsorption complexes

It must be remembered that, in general, the constants a and b of the van der Waals equation depend on volume and on temperature. Thus a number of variants are possible, and some of these and the corresponding adsorption isotherms are given in Table XVII-2. All of them lead to rather complex adsorption equations, but the general appearance of the family of isotherms from any one of them is as illustrated in Fig. XVII-11. The dotted line in the figure represents the presumed actual course of that particular isotherm and corresponds to a two-dimensional condensation from gas to liquid. Notice the general similarity to the plots of the Langmuir plus the lateral interaction equation shown in Fig. XVII-4. 

The Mechanism of Dehydration of Alcohols over Alumina Catalysts Herman Pines and Joost Manassen Complex Adsorption in Hydrogen Exchange on Group VIII Transition Metal Catalysts... 

In spite of these limitations, three examples of (salen)-metal complex adsorption have been described. In the first one, Jacobsen s complex (la-MnCl) was adsorbed on Al-MCM-41 [27] by impregnation with a solution of the complex in dichloromethane, an approach that prevents the possible cationic exchange. The results in the epoxidation of 1,2-dihydronaphthalene with aqueous NaOCl were comparable to those obtained in solution, with only a slight reduction in enantioselectivity (55% ee instead of 60% ee). However, recycling of this catalyst was not described. 

Of special interest in liquid dispersions are the surface-active agents that tend to accumulate at air/ liquid, liquid/liquid, and/or solid/liquid interfaces. Surfactants can arrange themselves to form a coherent film surrounding the dispersed droplets (in emulsions) or suspended particles (in suspensions). This process is an oriented physical adsorption. Adsorption at the interface tends to increase with increasing thermodynamic activity of the surfactant in solution until a complete monolayer is formed at the interface or until the active sites are saturated with surfactant molecules. Also, a multilayer of adsorbed surfactant molecules may occur, resulting in more complex adsorption isotherms. 

Limestone Methanol Complexation Adsorption Bacterial sulfate and iron reduction Methane production... 

An evaluation of the fate of trace metals in surface and sub-surface waters requires more detailed consideration of complexation, adsorption, coagulation, oxidation-reduction, and biological interactions. These processes can affect metals, solubility, toxicity, availability, physical transport, and corrosion potential. As a result of a need to describe the complex interactions involved in these situations, various models have been developed to address a number of specific situations. These are called equilibrium or speciation models because the user is provided (model output) with the distribution of various species. 

Iron Conversion to bathophenanthroline complex adsorption om anion exchange resin (Amberlite A27) Densitometric scanning of resin at 550 nm [350]... 

For any relationship between Z>L and Dml, assuming no complex adsorption, the steady-state complex concentration at the microorganism surface needed in equation (65) is based on the equality (except for sign) of the fluxes of L and ML, leading to ... 

As seen above (equation (5)), the basis of the simple bioaccumulation models is that the metal forms a complex with a carrier or channel protein at the surface of the biological membrane prior to internalisation. In the case of trace metals, it is extremely difficult to determine thermodynamic stability or kinetic rate constants for the adsorption, since for living cells it is nearly impossible to experimentally isolate adsorption to the membrane internalisation sites (equation (3)) from the other processes occurring simultaneously (e.g. mass transport complexation adsorption to other nonspecific sites, Seen, (equation (31)) internalisation). 

Here again, a number of models exist in the colloid science literature, ranging from very simple to very complex. Adsorption models employed for catalyst impregnation typically contain a chemical component (see [13,14,25] and references therein) for example, the proposed uptake of CPA by alumina shown in Figure 6.16. 

Adsorption and Precipitation vs heterogeneous Nucleation and Surface Precipitation. There is not only a continuum between surface complexation (adsorption) and precipitation, but there is also obiously a continuum from heterogeneous nucleation to surface precipitation. The two models are two limiting cases for the initiation of precipitation. In the heterogeneous nucleation model, the interface is fixed and no mixing of ions occurs across the interface. As a consequence precipi-... 

Competitive reactions, 24 37-43 It Complex adsorption in hydrogen exchange, 16 95 Complexes... 

If the anodic anion transfer (anionic adsorption, Eqn. 9-13a) to form an adsorbed metallic ion complex is the rate-determining step, the Tafel constant, a = 1 - p, win be obtained from Eqn. 9-14. If the anodic transfer of the adsorbed metallic ion complex (desorption of complexes, Eqn. 9-13b) is the rate-determining step, the Tafel constant, a = 2 - p, will be obtained from Eqns. 9-16 and 9-17. Similarly, if the cathodic anion transfer (anionic desorption, Eqn. 9-13a) is determining the rate, the Tafel constant in the cathodic reaction, a = 1 p, will be obtained from Eqns. 9-15 and 9-16 and if the cathodic transfer of a metallic ion complex (adsorption of complexes, Eqn. 9-13b) is determining the rate, the Tafel constant, a-sp, will be obtained from Eqn. 9-18. In this discussion we have assumed Pi = Ps P then, Eqns. 9-19 and 9-20 follow ... 

T Complex Adsorption in Hydrogen Exchange on Group VIII Transition Metal Catalysts... 

IV. Experimental Evidence for it Complex Adsorption and Reaction Mechanisms. 106... 

The present article is a review of tt complex adsorption which has recently been proposed in catalytic reaction mechanisms (2-11). The main evidence for this intermediate has been obtained from isotopic hydrogen exchange reactions with aromatic compounds where an interpretation according to classical theories has met with increasing difficulties. The limitations of the classical associative and dissociative exchange mechanisms originally proposed by Horiuti and Polanyi (12) and Farkas and Farkas (13-15) re discussed. This is followed by a... 

The decrease in activation energy for the chemisorption process as a result of 77 complex adsorption is readily explained by Lennard-Jones general theory of catalysis (19). Curve I in Fig. 1 represents the van der... 

Fig. 1. Decrease of activation energy in dissociative chemisorption by van der Waals adsorption (Bj), tr complex adsorption (E ), and resonance effects (Ei) Ej is activation energy of homogeneous reaction.

Waals interaction of a molecule with the catalyst surface. If a chemical bond can be formed with the surface, then a curve of type II exists. The point of intersection of curves I and II corresponds to the activation energy (Fj) of the reaction. The intersection of curves IV and II represents the activation energy of a homogeneous reaction. For 77 complex adsorption the situation is represented by curve III. Since 77 complex adsorption is stronger than van der Waals adsorption curve III will... 

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