Adsorption-desorption phenomena

Aggregated systems (solids, liquids, and gases) have two energy types  

Kinetic energy, Eq, or thermal energy-inducing particles (atoms or ions) with different possibilities of motions such as translation, rotation, and vibration. 

Interaction energy between particles, E such as van der Waals and electrostatic forces. 

The order of magnitude of these energies defines the system. 

Systems (b) and (c) are called condensed matter state, since the volumes are defined and less sensible to pressure variation. For condensed systems, the molecules on the surface or at the interface of another system present different situations  

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F. Ricca, Suppl. Nuovo Cimento 1, 5, 339 F. Ricca, C. Pisani and E. Garrone, Adsorption-Desorption Phenomena, Proc. 2nd. Intern. Conf. 1971, p. Ill, Academic Press, London and New York (1972) C, Pisani, F. Ricca and C. Roetti, J. Phys. Chem. 77, 657 (1973). 

Other Interaction Processes. The selectivity of flotation reagents in a pulp and their functions depend on their interactions with the mineral phases to be separated, but other physicochemical and hydrodynamic processes also play roles. AH adsorption—desorption phenomena occur at the sohd—hquid interfacial region. Surface processes that influence such adsorptions include activation and depression. Activators and depressants are auxiUary reagents. 

Haas, W.T. Grant, J.T. Dooley, D.J. Proc. 2nd Intern. Symp. on Adsorption/Desorption Phenomena Ricca, F. Ed. Academic Press London, 1973. 

When the applied electric field reaches a few volts per angstrom range, atoms on a surface, irrespective of whether they are lattice atoms or adsorbed atoms and of whether the surface temperature is high or low, may start to emit out of the surface in the form of ions. This high electric field produced evaporation phenomenon is usually called field evaporation if the surface atoms are lattice atoms, and is called field desorption if they are adsorbed atoms. From a theoretical point of view there are no fundamental differences. We will use the term field desorption for general purposes, especially for theoretical discussions, since desorption is the term used in many other adsorption-desorption phenomena. When we specifically mean removal of lattice atoms by electric field the term field evaporation will be used. Sometimes field evaporation is used where it may mean both field evaporation and field desorption. 

At present we have evidence for the complexity of higher temperature adsorption/desorption phenomena while, in general, the kinetic characteristics observed for many catalytic reactions are perhaps deceptively simple. The estimations of the concentrations of the participating surface intermediates are, in contrast, experimentally very difficult. Mechanistic investigations of many heterogeneous catalytic processes yield insufficient information to allow clear distinctions to be drawn between alternative reaction modelsf 125). 

A lattice theory of solutions has been proposed (.k) to describe the adsorption-desorption phenomena in zeolites. There are several reasons for this choice (a) forming a solid solution by two substances is analogous to the forming of an adsorbed phase in the cavities of a zeolite, (b) the theory of solutions is well understood and its mathematical techniques powerful, and (c) since the state-of-the-art in description of adsorption phenomena in... 

Electric field pulse methods have only recently been used to study adsorption-desorption phenomena on heterogeneous systems such as soils and soil constituents. This ingenious application is discussed in a later section. 

Ravikovitch P, Haller G and Neimark A V (1998) In Advances in Colloid and Interface Science, vols 76 and 77 (A V Neimark, ed) Elsevier, Amsterdam, p 203 Ricca, F, Pisani, C and Garrone, E (1971) In Adsorption-Desorption Phenomena, Academic Press, London, p 111... 

For all of these reasons, a thorough understanding of the NH3 adsorption-desorption phenomena on the catalyst surface is a prerequisite In fact, typical SCR catalysts can store large amounts of ammonia, whose surface evolution becomes the rate-controlling factor of the reactor dynamics. Also, mathematical modeling appears to be even more useful for the analysis and development of unsteady SCR processes than in the case of steady-state operation. 

The third class involves electroactive adsorbed species, yet it also encompasses the case in which, although originally inactive, the species is activated or modified in the adsorption process to give rise to the formation of electroactive adsorbed molecules. Obviously, all these effects discussed for the two previous classes are observed for this class, but additional effects are observed for the adsorbed species itself. Indeed, adsorption modifies (1) the concentration of the species at the electrode surface vis-a-vis that predicted from its bulk concentration, and (2) the energetics of the electron transfer reaction. The latter point arises because of additional thermodynamic contributions to be considered in the Rq/Ro or Po/P equilibria in Scheme 5 and also from changes in the reorganization energies. The former point leads to a variety of behaviors, since it is obviously a function of the kinetics of adsorption-desorption phenomena. A third additional effect of electroactive adsorbed species arises from their possible ability to act as electron transfer med-... 

The use of gas flow techniques are now widely recognized as important for the study of adsorption/desorption - phenomena at solid interfaces. Such studies are particularly important for the characterization of catalytically active sites on the surfaces of solids. One particular example is a study of the adsorption of ammonia onto activated carbon. It can be shown that adsorption of ammonia consists of reversible and irreversible steps and that these steps can be attributed to physisorp-tion for the former and adsorption on particular chemical groups for the latter. The heats of adsorption for various sites can be measured and the data can be used to reveal the existence of a wide distribution of acid sites that are accessible to ammonia to varying degrees. 

G. Rovida, E. Ferroni, M. Maglietta, and F. Pratesi in Adsorption-Desorption Phenomena , ed. F. Ricca, Academic Press, London, 1972, 417. 

Since the adsorption of reactants and desorption of products are unavoidable and fundamental steps of heterogeneous catalysis, there is a need of understanding the kinetics of adsorption-desorption phenomena on heterogeneous surfaces. In practically all situations the reaction involves two or more reactants, so that chemically interesting kinetics are multicomponent. This is immediately understood either considering the Rideal mechanism ... 

G. Ertl. and J. Koch, in Adsorption-Desorption Phenomena, Ed. F. Rica (Academic Press, New York, (1972), p.345. 

A number of soil chemical phenomena are characterized by rapid reaction rates that occur on millisecond and microsecond time scales. Batch and flow techniques cannot be used to measure such reaction rates. Moreover, kinetic studies that are conducted using these methods yield apparent rate coefficients and apparent rate laws since mass transfer and transport processes usually predominate. Relaxation methods enable one to measure reaction rates on millisecond and microsecond time scales and 10 determine mechanistic rate laws. In this chapter, theoretical aspects of chemical relaxation are presented. Transient relaxation methods such as temperature-jump, pressure-jump, concentration-jump, and electric field pulse techniques will be discussed and their application to the study of cation and anion adsorption/desorption phenomena, ion-exchange processes, and hydrolysis and complexation reactions will he covered. 

Chemical relaxation theory was presented in this chapter, and a number of transient relaxation techniques including t-jump, p-jump, c-jump, and electric-field pulse were discussed. The application of these methods to important soil chemical processes was also covered including anion and cation adsorption/desorption phenomena, hydrolysis of soil minerals, ion-e.xchangc processes, and complexation reactions. Relaxation methods have... 

Calvet, R. (1980) Adsorption-desorption phenomena. In Interactions between Herbicides and the Soil, ed. R.J. Hance, pp. 1-29. London Academic Press. 

L. A. Peterman, in F. Ricca (Ed.), Adsorption—Desorption Phenomena, Academic Press, New York, 1972, p. 277. 

For Ba2CoW06, the TPR showed a little CO consumption at 655 K and can be related to adsorption-desorption phenomena. 

Flow adsorption calorimetry is recognized as an important method to study adsorption/desorption phenomena at solid-fluid interfaces. According to a review by Groszek [37], flow adsorption microcalorimetiy is now developed to a point where it provides accurate and reliable adsorption and desorption data for events occurring at the solid-liquid or gas-solid interface over a wide range of temperatures, pressures and solution concentrations. 

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