Adsorbate-adsorbent bond

Quantum-chemical calculations make it possible to specify these types of adsorbent-adsorbate bonds more precisely. For instance, on the faces (100) and (111) of single crystals, three types of bonds are singled out that differ in the arrangement of an adsorbed particle (1) a particle over an atom of the solid (2) a particle over the bond between adjacent atoms and (3) a particle over an interstice of atoms of the solid. The coexistence of adsorbent-adsorbate bonds is considered by a transition to an auxiliary inhomogeneous lattice whose constant is smaller than that of the lattice of the solid s atoms and to the distribution thereon of larger particles. 

The activity of a catalyst depends on the nature, the number, the strength and the spatial arrangement of the chemical bonds that are transiently created between the reactants and the surface. The objective of the chemical characterization of the surface is a detailed description of the adsorbate-adsorbent bonds that a given catalyst will develop when contacted with a given reaction mixture. Therefore, chemical characterization should be done in situ in the course of the reaction itself. However, because of experimental limitations, this is seldom possible and catalyst surfaces are usually characterized by means of separate experiments. It is important to characterize the catalyst surface both before and after its use in a reaction. 

The analysis of multilayer adsorption follows that of Langmuir for monomoleeular adsorption. Adsorbate-adsorbent bonding is involved in the first layer while adsorbate-adsorbate bonding is involved in forming all subsequent layers. The heat of adsorption for the first layer, Eads, is very different from that for subsequent layers where the heat of adsorption is assumed to be the same as the heat of liquefaction, Enq (only approximately true). The mathematieal derivation of the... 

The zeta potential decreases as increases. The values of Ceq. which corresponds to C = 0, highest plateau of the isotherm curves (Figures 7 and 8). Beyond this plateau ( is negative. If one considers that the normal adsorbate-adsorbent bond is mainly of electrostatic type, the Ceq. values corresponding to () = 0 coincide with the monolayer. In this case it is possible to normalize the isotherm curves by dividing Q by Qo which is the value of Qa corresponding to the monolayer ... 

Another point in interpreting infrared spectra of adsorbed layers is the coupling interaction between adsorbates. This primarily depends on the nature of the adsorbate-adsorbent bond. For CO this bond is mainly covalent-dative, while for NO it is mostly... 

The preexponential factors for each of the reaction steps can, in principle, be estimated using either gas kinetics or transition state theory. Desorption occurs when the adsorbate-adsorbent bond acquires the required activation energy for desorption in the form of vibrational energy. To a first approximation the vibrational frequency can be assumed to be approximately 10 s for the temperature at which desorption proceeds at a significant rate. The frequency of bond rupture is given by... 

The consequence of the localization of the charge is that the strength of the adsorbate-adsorbent bond will only be significantly modified if adsorption occurs... 

Another problem eonneeted with the frustrated modes at the surfaee is their influenee on the intramoleeular vibrations of the adsorbed moleeule. Nitzan and Persson [30] suppose that the high-frequeney intramoleeular vibrations of adsorbed moleeules interaet with the phonons of the solid via low-frequeney oseillations of the adsorbent—adsorbate bond, the latter being regarded as frustrated translational and rotational degrees of freedom of the adsorbed moleeule. In the quantum ease the Hamiltonian of the system ean be expressed as... 

Information on the binding energy, deduced from calorimetric data, is needed to achieve a theoretical description of the adsorbate-adsorbent bond. It has been shown, for instance, that, in the case of the adsorption of hydrogen on nickel-copper alloys, a correlation between heats of adsorption and surface magnetic properties can be found. The correlation indicates that the energy of the bond between adsorbed hydrogen and nickel atoms is regulated by the electron density of states, near the Fermi level, for the metal surface [6-8]. 

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