Adsorption energies, calculation

Fortuitously, the adsorption energies obtained using the VASP code (calculated according to equation (i)) are in excellent agreement with experimentally reported values for the Ag monolayer deposited on top the MgO support (see Fig. 6). But for the two noble metals studied the adsorption energies obtained with CR98 are overestimated by approx. 100% compared to adsorption energies calculated with the... 

The conclusive proof came only recently and was based on MgO single crystal experiments. A single crystal surface is expected to have a small number (almost negligible) of defects. On a UHV cleaved MgO single crystal [85,86], the CO thermal desorption spectra (TDS) showed a peak at T 57 K and a broad feature at 76 K. The adsorption energy, calculated via the Redhead equation... 

In this paper, a modified HK method is presented which accounts for spatial variations in the density profile of a fluid (argon) adsorbed within a carbon slit pore. We compare the pore width/filling pressure correlations predicted by the original HK method, the modified HK method, and methods based upon statistical thermodynamics (density functional theory and Monte Carlo molecular simulation). The inclusion of the density profile weighting in the HK adsorption energy calculation improves the agreement between the HK model and the predictions of the statistical thermodynamics methods. Although the modified Horvath-Kawazoe adsorption model lacks the quantitative accuracy of the statistical thermodynamics approaches, it is numerically convenient for ease of application, and it has a sounder molecular basis than analytic adsorption models derived from the Kelvin equation. 

The key step in the derivation by Reuter et al. of their lattice model is the use of detailed balance to determine the sticking coefficients for each species on each type of site.31 The total adsorption rate at a particular site can be expressed as Tad = SI(p, T), where S is the local sticking coefficient and I(p,T) is the impingement rate of the species of interest from a gas phase with partial pressure p and temperature T. At steady state, the total adsorption and desorption rates must satisfy the detailed balance condition TdesjTad = exp[(Fb—/j,(T, p))/kT, where Fb is the free energy of the adsorbed species and fi(T, p) is the chemical potential of the gas phase species. The adsorption free energy is well approximated by the adsorption enthalpy, which is simply the adsorption energy calculated by a DFT calculation. This approach provides a direct link between the adsorption and desorption rates and the pressure and temperature of the bulk gas phase. 

Figures 10.10 shows PDOS changes of the metal valence electron density and CO adsorbed atop and threefold calculated using periodical DFT/VASP [5] calculations. Calculated adsorption energies of CO are 190 and 180 kj mol"S respectively. Not withstanding the difference with the ADF (A.L. Yakovlev and R.A. van Santen, 2005, unpublished), calculated adsorption energies calculated for the Ru cluster of Figure 10.8 electronic features of the admolecular bond are quite similar. It illustrates the complementarity of both approaches.

Sohail and Qadeer studied the adsorption of Pb(II) ions from aqueous solutions on commercial activated carbons and determined optimum conditions for maximum adsorption in terms of the time of contact, solution concentration, and temperature. The adsorption was found to obey first-order kinetics. The magnitude of adsorption energy calculated from D-R equation was found to be 7.61 KJ/mol, which showed that the adsorption involved weak bonding between the Pb + ions and the activated carbon surface, Yang et al. used two activated carbons obtained from coal for... 

The adsorption energy calculated by this method is the maximum adsorption energy (i.e. tZ + aED-... 

The adsorption energies calculated for the adsorption of methanoic acid on the minimized hydroxylated quartz surfaces are summarized in Table 3.6. The methanoic acid adsorption energy was... 

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. 

Here, too, it is practicable to use the fraction A21of specific adsorption energy calculated per sublayer B rather than the specific sublayer energy U. By definition,... 

Table 2.1 reports average adsorption energies for each of the 10 O adsorption sites on Pt(321) in order of inereasing average adsorption energy, calculated in a 2x2 supercell with one adsorbate per supereell (Na = 1) to simulate isolated adsorbates. Atomic energies eannot be aeeurately evaluated within the... 

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