Chemisorption


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chemisorption

[′kem·i‚sȯrp·shən]
(physical chemistry)
A chemical adsorption process in which weak chemical bonds are formed between gas or liquid molecules and a solid surface.

Chemisorption

 

the adsorption of substances from the surrounding medium by a liquid or solid, accompanied by the formation of chemical compounds. In a narrower sense, chemisorption is regarded as the chemical binding of a substance by the surface of a solid, or chemical adsorption.

Considerable heat is released in chemisorption: the heat of chemisorption is usually 84–126 kilojoules per mole (kJ/mole), or 20–30 kcal/mole; in some cases—for example, the chemisorption of oxygen on metals—it may exceed 420 kJ/mole (100 kcal/mole). Like chemical reactions, chemisorption usually requires considerable activation energy. Thus, chemisorption is accelerated when the temperature is increased (activated adsorption). Chemisorption is selective—that is, it depends on the chemical affinity of the adsorbed substance for the solid surface.

Physical methods, such as spectroscopy, electron paramagnetic resonance, nuclear magnetic resonance, electron and ion field-emission microscopy, and slow-electron diffraction, are used to study chemisorption. The process plays an important role in heterogeneous catalysis, gas purification, and vacuum technology.

REFERENCES

See references under ADSORPTION.

M. U. KISLIUK

References in periodicals archive ?
The Isotherm profiles obtained from copper ions adsorption are similar to those reported from the [Cu.sup.+2] adsorption on goethite and [gamma]-[Al.sub.2][O.sub.3], and Ti[O.sub.2] surfaces, confirming specific adsorption or chemisorption between [Cu.sup.+2] ions and oxide surface [20, 21].
The regioselective chemisorption of Au (III) complex ions, which were present on the surface of TiO2 enabled Au and Pt nanoparticles to be deposited separately.
and Otto, K., "Chemisorption of Alkenes on Copper-Exchanged ZSM-5 Zeolite," Catal.
Here, n was an indicator of the degree of nonlinearity between water concentration and sorption (n = 1 denotes linear adsorption, n < 1 a chemisorption, and n > 1 physisorption [76]).
For this model, the sorption process is controlled by chemisorption, and the sorption capacity is controlled by the number of the active sorption sites.
Change in standard adsorption enthalpy ([DELTA][H.sup.0.sub.ads] = -168 kJ[mol.sup.-1]) is negative, showing an exothermic adsorption process, and its absolute value is higher than 100 kJ[mol.sup.-1], which is according to the literature [38] not a typical chemisorption when referring to the values of [DELTA][G.sup.0.sub.ads].
Deisl et al., "H on Pt(110): An atypical chemisorption site at low coverages," Physical Review B: Condensed Matter and Materials Physics, vol.
This leads to the increase of inhibition efficiency and suggests that the inhibitor molecules act by adsorption on the steel surface in the acid medium which is a characteristic of chemisorption [4].
The kinetic curves show that both dissociative chemisorption and physisorption, which are responsible for the atomic and molecular hydrogen accumulation, take place during the hydrogen adsorption.
Hydrogen consumption and metal dispersion is determined by chemisorption at 30[grados]C using an atomic ratio H/M = 1 (M = Pt or Pd).
The value of activation energy was found to be 75.29 kJ mol-1.On the basis of kinetic parameters determined at different temperatures and value of activation energy, chemisorption can be assumed as rate controlling mechanism for aqueous Cu (II) adsorption onto turmeric surface.
Because of this greater affinity, there will be more interactions between [Cd.sup.2+] and the charcoal surface, justifying the chemisorption and the results found.