Chemisorption reactions

INS Ion neutralization An inert gas hitting surface is spectroscopy [147] neutralized with the ejection of an Auger electron from a surface atom Spectroscopy of Emitted Ions or Molecules Kinetics of surface reactions chemisorption... 

MBRS Molecular beam spectroscopy [158] A modulated molecular beam hits the surface and the time lag for reaction products is measured Kinetics of surface reactions chemisorption... 

Kinds of Catalyzed Organic Reactions A fundamental classification of organic reactions is possible on the basis of the lands of bonds that are formed or destroyed and the natures of eliminations, substitutions, and additions of groups. Here a more pragmatic hst of 20 commercially important lands or classes of reactions will be discussed. In all instances of sohd-catalyzed reactions, chemisorption is a primary step. Often molecules are dissociated on chemisorption into... 

Adsorption of Reagents and Product of Reaction. Chemisorption of Oxygen. During the adsorption of the first doses of oxygen on NiO(250), the equilibrium pressure being of the order of 10"3 torr, the... 

Infrared spectroscopy was used to gain a better understanding of the mechanism of photocatalytic oxidation of TCE (Fan and Yates, 1996). IR spectroscopy also was used to determine intermediates formed from the reaction. Chemisorption of oxygen onto the TiOz surface plays an important role in the oxidation of TCE. The reaction was also temperature dependent. TCE is more easily degraded in the gas phase than in the aqueous phase. For this reason, a process that strips TCE from the groundwater and then treats the vapor containing TCE can be used. 

Henglein, A. Physicochemical properties of small metal particles in solution Microelectrode reactions, chemisorption, composite metal particles, and the atom-to-metal transition, J. Phys. Chem. 1993, 97, 5457. 

The only important exception, in which kc < ki has to be assumed, is the chemisorption of a gas component from a gas mixture in flue gas scrubbing, since here depletion of the gas to be adsorbed is involved and in addition the concentration of the gas is already zero at the interface due to the extremely fast chemical reaction (chemisorption). Since gas scrubbing is not normally carried out in stirred tanks, this exception will not be considered here. 

The above scheme shows the importance of both adsorption and desorption processes. Adsorption of at least one of the reactant molecules is required for catalysis to occur. If the accelerated rate of reaction is simply due to the concentration of molecules at the surface, catalysis may result from physisorption of the reactants. On the other hand, chemisorption can be used primarily to quantitatively evaluate the number of surface active sites, which are likely to promote (catalyze) chemical reactions. Chemisorption analyses are applied to physically characterize a catalyst material, to determine a catalyst s relative efficiency in promoting a particular reaction, to study catalyst poisoning, and in monitoring the degradation of catalytic activity over time of use. 

The above mentioned equations were used due to the fact that the first one describes well the initial stage of dyes sorption, the second equation fits well experimental data in the whole range of process time for most adsorbate/adsorbent systems. Moreover, using these equations the dyes sorption process is considered as a chemical reaction (chemisorption) [46-52]. 

Most of the above uses rely on physisorption rather than strong chemical bond formation. Chemisorption, however, is of particular importance in heterogeneous catalysis, where it is a necessary precursor to reaction. Chemisorption sites include Bronsted and Lewis acid sites as well as coordinatively unsaturated transition metal cations, either within the framework or as charge-balancing cations outside the frameworks. Their catalytic activity is discussed further in the following Chapters 8 and 9. 

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