Rutile, adsorption energies

Figure 5.12 Adsorption energy and surface coverage, (a) Physical adsorption of nitrogen on rutile at 85 K71. (b) Chemisorption of hydrogen on tungsten169, (c) Physical adsorption of krypton on graphitised carbon black166. (See Figure 5.6) (By courtesy of (a) Science Progress, (b) Discussions of the Faraday Society and (c) The Canadian Journal of Chemistry)...

A further analysis of the various contributions toward the adsorption energies (135) has revealed that the adsorption energy of alcohol on rutile consists mainly of the contribution of the attraction of the dipole the nonpolar van der Waals forces contribute less than 40% of this part and electrostatic polarization less than 10%. The adsorption energies of hydrocarbons on rutile are mostly due to the van der Waals forces, and half the amount of the van der Waals contribution (one third of the total) originates from the electrostatic polarization. 

Values of A, 4 for nitrogen adsorption at 0 = 0.1 are recorded in Table 10.13, which also contains the corresponding adsorption energy data for silica-coated rutile. It was independently confirmed that the surface properties of the latter sample, which had a coating of 2.6% dense silica, were very similar to those of pure silica (Furlong etal., 1980). 

An adsorption of silver dimer on a rutile (110) surface has been studied using a DFT model within both cluster and periodic approaches. The calculations show that the interaction of silver dimers can occur both with bridging chain of oxygen atoms or with atoms located in the hollows between chains. The bonding of Ag2 in the hollow is characterized by the positive adsorption energy according to the periodic model. On the other hand, the geometry optimization of similar structures within the cluster model leads to desorption or dissociation of silver dimer. The periodic model is shown more appropriate for this system. 

Fig. 3-2. Correlation of adsorption energy on rutile with adsorbate dipole moment. Reprinted by permission of the National Research Council of (Canada, from the Canadian Journal of Chemistry (23).

Figure 12 Adsorption energy distribution for argon on rutile from the data of Drain and Morrison...

Table 11.10. MSINDO adsorption energies (kJ/mol) for water adsorption on rutile (110) (relaxed cluster calculations), [770]...

The adsorption energies calculated with these small cluster models are presented in Table 11.10. The geometries of the clnsters were optimized within the symmetry of the rutile structure. In model B, there are one or two more degrees of freedom for oxygen atoms in nonlattice positions. 

Energy minimizations of the corresponding slabs led to similar adsorption energies for both structures, which were lower than the corresponding associative values for 1/2 monolayer coverage by 3-5 kcal/mol. Thus, these results are in accordance with previous DFT simulations for half-monolayer coverage that predict H2O dissociation on the rutile (110) surface. 

Fig. 23 Electron injection times vs adsorption energy for different anchoring groups (a—o) for anatase (101) and rutile (110). Reprinted with permission of [290]. Copyright (2012) American Chemical Society...

Table 5 Adsorption configurations of N3 on the rutile (110) slab, their adsorption energies and injection times...

Munuera and Stone (142) successfully applied the model of a (110) plane to their adsorption studies of water, isopropanol, and acetone. The dry (110) face exposes 5.1 five-coordinate Ti4+ ions. Half of these were able to chemisorb water dissociatively, leading to the formation of two types of surface OH groups. The activation energy for desorption of this water was 107 kJ mole-1. At this state of hydroxylation the rutile surface consists of isolated five-coordinated Ti4+ ions, which on further addition of water coordinate water molecu-larly, of isolated O2- ions, and of pairs of OH groups, one being monodentate and the other bidentate with respect to the cations. 

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