Adsorption strong interaction

At low adsorbate loadings, the differential heat of adsorption decreases with increasing adsorbate loadings. This is direct evidence that the adsorbent surface is energetically heterogeneous, ie, some adsorption sites interact more strongly with the adsorbate molecules. These sites are filled first so that adsorption of additional molecules involves progressively lower heats of adsorption. 

The adsorption energy of N2 is also low, but that of NO on the (100) surface is substantial. Notwithstanding the very similar activation energies for N2 and NO formation (see Tables 1.4 and 1.5), the strong interaction of NO with both surfaces implies that the selectivity of the reaction toward N2 will be high at low temperatures. The NO once formed will not desorb and can only be removed as N2O. 

H2O adsorbs strongly on both Au and Ti02. However, the influence of water on the catalyst or reaction is negligible [2]. PO is known to strongly interact with Ti02, and adsorption, desorption, and decomposition of PO are independent on the presence of gold [3]. 

Upon adsorption, there is again a strong interaction of the 5a and 2jt orbitals and the metal sp electrons, resulting, as above, in a downward shift and broadening of these two levels. Also, in this case the variation of the adsorption energy is accounted for by the interaction with the d band of the metal, which will cause the levels to split into bonding and antibonding parts. The result is shown in Fig. 6.32, which should be seen as a realistic alternative to the more qualitative representation of Fig. 6.25. 

The requirement for atomic-scale sites in the CT mechanism is thought to be due to the formation of adatom-adsorbate complexes. Such complexes require a coordination site on the adsorbate through which the strong interaction can occur, as was demonstrated by the controlled adsorption of isonicotinic acid and benzoic acid on thin island films of silver (see the work of Chen et ai, 1980). This clearly showed that SERS spectra could only be obtained from the molecules when coordinating sites were exposed to the Ag film. 

One of the simplest methods of attaching biomolecules to hydrophobic polymeric particles is the use of passive adsorption. Some of the earliest examples related to the use of particles in immunoassays include the use of non-covalently adsorbed antibody or antigen onto latex microspheres. Protein adsorption onto hydrophobic particles takes place through strong interactions... 

The physical properties of probe molecules adsorbed in the confined space of porous materials are known to vary in dependence of structural constraints on molecular motion. Detailed investigations of adsorption geometries are possible, when well-defined sites and loadings exist. This was the case for the adsorption of strongly interacting probe molecules, such as pyridine, on SiOH groups in the... 

MgO is a basic metal oxide and has the same crystal structure as NiO. As a result, the combination of MgO and NiO results in a solid-solution catalyst with a basic surface (171,172), and both characteristics are helpful in inhibiting carbon deposition (171,172,239). The basic surface increases C02 adsorption, which reduces or inhibits carbon-deposition (Section ALB). The NiO-MgO solid solution can control the nickel particle sizes in the catalyst. This control occurs because in the solid solution NiO has strong interactions with MgO and, as indicated by TPR data (26), the former oxide can no longer be easily reduced. Consequently, only a small amount of NiO is expected to be reduced, and thus small nickel particles are formed on the surface of the solid solution, smaller than the size necessary for coke formation. Indeed, the nickel particles on a reduced 16.7 wt% NiO/MgO solid-solution catalyst were too small to be observed by TEM (171). Furthermore, two additional important qualities stimulated the selection of MgO as a support its high thermal stability and low cost (250,251). 

The bottom spectrum was obtained by cycling the electrode in CO-free SnCl /HjSO solution to ensure formation of a partial Sn adlayer and then replacing the cell contents with CO-saturated solution. The v(C0) band is still observed, which shows that the Sn adatoms do not saturate the surface even in the absence of competitive CO adsorption. The intensity and frequency of the v(C0) band have both decreased, which confirms that the CO adlayer is only partially complete. There is no evidence for a change in v(C0) beyond that expected for the coverage dependence expected in acid solution. This shows that there is no strong interaction between adsorbed CO molecules and neighboring Sn adatoms, in support of the assumptions used in the adatom oxidation model discussed above. 

Since it was initially reported [21], several methods have been presented in order to attach DNA onto CNTs, including adsorption. First, transmission electron microscopy showed that the DNA molecules tended to cover the surface of the nanotubes evenly, suggesting a strong interaction with the carbon surface [24]. 

Stabihzation may also be achieved by altering reaction conditions (e.g., pH, temperature, ionic strength, etc.). In other instances, loss of activity may attend the adsorption of the enzyme to the walls of the reaction container (e.g., glass or plastic can strongly interact with proteins). Using a different container or simply including a spectator protein (e.g., albumin) may increase the degree of stability. 

As an example of strong interaction leading to localized adsorption we have the figures for the entropy of adsorption of water on different adsorbents, which are summarized in Table X. In all cases the heat of adsorption is quite large and the entropy values for the adsorbed material... 

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