Desorption phenomena

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. 

Menzel, D. (1975) Desorption phenomena In Interactions on Metal Surfaces (R. Gomer, ed.), Springer-Verlag, New York, pp. 102-43. 

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. 

An additional difficulty in studies of slow chemisorption is evidenced by the Taylor-Liang technique of measuring adsorption isobars at successively higher temperatures without pumping between runs, a technique that has been reviewed in an earlier volume of this series (8). The ad-sorption-desorption phenomena observed between room temperature and about 150°C. clearly show in this temperature range the existence on the surface of zinc oxide of two types of hydrogen chemisorption (9). 

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. 

Many investigators have found that in soil-pesticide studies sorption-desorption phenomena may be nonsingular or even irreversible (Farmer... 

The film phenomena influence the process variables along the column. The partial pressures of SO2 and CO2 are shown in Fig. 9.24. It can be seen that CO2 is absorbed in the fresh alkaline solution at the column top. Then, as the pH decreases from the top to the bottom due to SO2 absorption, the CO2 concentration increases, and the direction of the CO2 flux at the interface changes (see Fig. 9.25). CO2 desorption also occurs when the concentration in the reaction plane is higher than that at the interface, even if in the bulk it may be lower [70], The co-existence of absorption and desorption phenomena shown in Figures 9.24 and 9.25 is similar to the phenomena discussed elsewhere [104]. Further sensitivity studies regarding the effect of the buffer concentration and SO2 gas concentration can also be found [70]. 

Thus, in this review we present the desorption phenomena focused on the rotational and translational motions of desorbed molecules. That is, we describe the DIET process stimulated by ultraviolet (UV) and visible nanosecond pulsed lasers for adsorbed diatomic molecules of NO and CO from surfaces. Non-thermal laser-induced desorption of NO and CO from metal surfaces occurs via two schemes of DIET and DIMET (desorption induced by multiple electronic transitions). DIET is induced by nanosecond-pulsed lasers and has been observed in the following systems NO from Pt(0 0 1) [4, 5],... 

As the quantities of elements applied in nuclear chemistry are often small, down to one-atom-at-a-time, deposition and volatilization are predominately related to adsorption and desorption phenomena, respectively. Practically, pure condensed phases do not occur. The volatilization and the gas phase transport through a chromatography column depend on... 

Desorption Phenomena, Academic Press, New York, 1972, p. 215 and subsequent papers. See also Thorpe, B. J. Surf. Sri. 33, 306 (1972). 

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... 

The molar volume change AV° is small for most reactions in solution, which requires large pressure changes (>50 atm) for a measurable perturbation of an equilibrium [30], This technique has not found much use in electron-transfer reactions, but various absorption-desorption phenomena, association-dissociation equilibria, and structural relaxations have been studied successfully. Pressure jump is also quite useful in biological studies of folding and unfolding of proteins and DNA owing to the pressure sensitivity of these processes [31],... 

Muramatsu Y., Uchida S., Sriyotha P., and Sriyotha K. (1990) Some considerations on the sorption and desorption phenomena of iodide and iodate on soil. Water Air Soil Pollul 49, 125-138. 

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. 

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