Adsorption-desorption processes

XVIII-11 (the paradox of desorption heat exceeding adsorption heat is explainable in terms of a partial irreversibility of the adsorption-desorption process). 

For adsorbed hydrocarbons, the adsorption—desorption process can be thought of as a reaction and the adsorption isotherm as a description of the reaction at equihbtium. For the Langmuir isotherm,... 

The above stm study also discovered a facile transport of surface gold atoms in the presence of the Hquid phase, suggesting that the two-step mechanism does not provide a complete picture of the surface reactions, and that adsorption/desorption processes may have an important role in the formation of the final equiHbrium stmcture of the monolayer. Support for the importance of a desorption process comes from atomic absorption studies showing the existence of gold in the alkanethiol solution. The stm studies suggest that this gold comes from terraces, where single-a tomic deep pits are formed (281—283). 

The quantitative solution of the problem, i.e. simultaneous determination of both the sequence of surface chemical steps and the ratios of the rate constants of adsorption-desorption processes to the rate constants of surface reactions from experimental kinetic data, is extraordinarily difficult. The attempt made by Smith and Prater 82) in a study of cyclohexane-cyclohexene-benzene interconversion, using elegant mathematic procedures based on the previous theoretical treatment 28), has met with only partial success. Nevertheless, their work is an example of how a sophisticated approach to the quantitative solution of a coupled heterogeneous catalytic system should be employed if the system is studied as a whole. 

In general, the flow rate F(t) consists of the following additive components the controlled flow rate Fd of the entering gas, the flow rate Fi which is due to parasitic leaks and/or diffusion, and the flow rate Fw resulting from possible adsorption-desorption processes on the system walls (in Section I, references are given to papers dealing with the elimination or control of the wall effects in the flash filament technique). In each of these flow rate components a particular ratio of the investigated adsorbate and of the inert gas exists and all these components contribute to the over-all mean values Fh(t) and F (t). 

Figure 30. Adsorption-desorption process of ions on the nickel surface in NaCl solution at the critical state, which was concluded from the experimental results shown in Figs. 26 to 29.

The concept of H2 chemisorbing on Rh as a molecular species may appear at first to be contradictory to other studies e.g.. Isotope exchange and TPD but It Is not, given the existence of klnetlcally distinct sites. An adsorption/desorption process can occur on a specific site via ... 

Exchangeable ions (EXC), sometimes including ions nonspecifically adsorbed and specifically absorbed on the surface of various soil components, such as carbonate, organic matter, Fe, Mn, Si, and Al oxides, and clay minerals. This part is controlled by adsorption-desorption processes. 

It is interesting to note that, although the intrinsic rate of desorption is slower than that of adsorption, both rates were found to be sufficiently fast under our experimental conditions so that the adsorption-desorption process on the Pt surface can be assumed to rapidly equilibrate at all times that is, even a ten-fold increase in both the adsorption and desorption rate constants (while keeping their ratio constant) did not significantly change the predicted step responses. With the assumption of chemisorption equilibrium, Equations (1) and (4) can be combined into the form (35)... 

Adsorption of acetic acid on Pt(lll) surface was studied the surface concentration data were correlated with voltammetric profiles of the Pt(lll) electrode in perchloric acid electrolyte containing 0.5 mM of CHoCOOH. It is concluded that acetic acid adsorption is associative and occurs without a significant charge transfer across the interface. Instead, the recorded currents are due to adsorption/desorption processes of hydrogen, processes which are much better resolved on Pt(lll) than on polycrystalline platinum. A classification of adsorption processes on catalytic electrodes and atmospheric methods of preparation of single crystal electrodes are discussed. 

Figure 12.6 shows a scheme of the laboratory equipment used to test this set-up. Figure 12.7 is an example of the iodate concentration versus bed volume (BV) plot during one cycle of the adsorption-desorption process. Figure 12.8 shows the influence of the resin size on the extent of iodate removal. The particle size of the resin greatly influences the removal. The fluidised bed volume increases as the diameter of the resin reduces. 

Valenti LE, Fiorito PA, Garcia CD, Giacomelli CE (2007) The adsorption-desorption process of bovine serum albumin on carbon nanotubes. J. Colloid Interface Sci. 307 349-356. 

To interpret the kinetics experimental data of an organic pollutant(s) or leachate from complex organic mixtures, it is necessary to determine the adsorption/ desorption process steps in a given experimental system which govern the overall adsorption/desorption rate. For instance, the adsorption process of an organic compound by a porous adsorbent can be categorized as three consecutive steps ... 

H2PO4, are suggested to undergo a redox adsorption/desorption process in which ions are always involved. 

Buffered mobile phases are inherently used to adjust and control the adsorption-desorption process. These CSPs are especially useful for the separation of very polar charged analytes, such as sulphonic acids. Chiral anion-exchangers are the most successful CSPs and among them the cinchona alkaloids, quinine and quinidine (Figure... 

Here, we do not discuss P transformation resulting from chemical equilibrium and adsorption-desorption processes the reader is directed to the comprehensive... 

Liu C, Zachara JM, Smith SC, McKinley JP, Ainsworth CC (2003) Desorption kinetics of radiocesium from subsurface sediments at Hanford Site USA. Geochim Cosmochim Acta 67 2893-2912 Loffredo E, Senesi N (2006) Eate of anthropogenic organic pollutants in soils with emphasis on adsorption/desorption processes of endocrine disruptor compounds. Pure App Chem 78 947-961... 

Undabeytia T, Morillo E, Ramos AB, Maqueda C (2002) Mutual influence of Cu and a cationic herbicide on their adsorption-desorption processes on two selected soils. Water, Air Soil Poll 137 81-94B... 

Paulis, M Gandia, LM Gil, A Sambeth, J Odriozola, JA Montes, M. Influence of the surface adsorption-desorption processes on the ignition curves of volatile organic compounds (VOCs) complete oxidation over supported catalysts, Appl. Catal, B Environmental, 2000, Volume 26, Issue 1, 37-46. 

For singular adsorption-desorption processes where N = 1, R becomes... 

The adsorption-desorption process is of interest in many systems (such as with cement). The water vapor may condense in the pores after adsorption under certain conditions. This may be studied by analyzing the adsorption-desorption data... 

On any solid surface, there are a certain number of possible adsorption sites per gram (Nm), where any adsorbate can freely adsorb. There will be a fraction 0 of sites which are filled by one adsorbing solute. There will also exist an adsorption-desorption process at the surface. The rate of adsorption will be given as... 

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