Transition adsorption energy

In the case of Gaussian and uniform distributions of the adsorption energy, the smearing of the phase transition region in the the first as well as higher layers was observed. Thus, insead of vertical jumps, the adsorption isotherms exhibited only finite slope even at quite low temperatures. This result is consistent with the predictions of Dash and Puff [32]. 

Fig. 5(a) contains the oxygen and hydrogen density profiles it demonstrates clearly the major differences between the water structure next to a metal surface and near a free or nonpolar surface (compare to Fig. 3). Due to the significant adsorption energy of water on transition metal surfaces (typically of the order of 20-50kJmoP see, e.g., [136]), strong density oscillations are observed next to the metal. Between three and four water layers have also been identified in most simulations near uncharged metal surfaces, depending on the model and on statistical accuracy. Beyond about...

In this figure, the activation energies of N2 dissociation are compared for the different reaction centers the (111) surface structure ofan fee crystal and a stepped surface. Activation energies with respect to the energy of the gas-phase molecule are related to the adsorption energies of the N atoms. As often found for bond activating surface reactions, a value of a close to 1 is obtained. It implies that the electronic interactions between the surface and the reactant in the transition state and product state are similar. The bond strength of the chemical bond... 

Describe the trend in adsorption energy for atoms such as N and O when going from left to right through the transition metals in the periodic table. Do the same for going vertically through the transition metals. 

Abild-Pedersen F, Greeley J, Studt F, Moses PG, Rossmeisl J, Munter T, Bligaard T, Ndrskov JK. 2007. Scaling properties of adsorption energies for hydrogen-containing molecules on transition-metal surfaces. Phys Rev Lett 99 016105. 

The Adsorption Energies (eV) of Atomic Carbon Adsorption (a) on Different Transition Metals and Their Alloys and (b) on Different Adsorption Sites of the Ni Surfaces... 

Figure 2.16. Calculated dissociative nitrogen ( ), carbon monoxide ( ), and oxygen ( ) chemisorption energies over different 3d transition metals plotted as a function of the center of the transition metal rf-bands. A more negative adsorption energy indicates a stronger adsorbate-metal bond. Reproduced from [32].

Trends in adsorption energies on transition metal surfaces... 

As an introduction to the problem of understanding trends in adsorption energies on metal surfaces, consider the adsorption of atomic oxygen on a range of late transition metal surfaces. Figure 4.1 shows calculated energies as a function of the... 

Figure 4.1. Calculated adsorption energy for atomic oxygen as a function of distance of the atom above the surface for a range of close-packed transition metal surfaces (ordered according to their position in the periodic table). In the box showing results for Ru, the energy per atom in 02 is shown for comparison. Only metals where the minimum in the adsorption energy function is below this value will be able to dissociate 02 exothermally. Adapted from Ref. [4].

Since all transition metals have a half filled, broad s band, we will assume, in the spirit of the preceding section, that this part is independent of the metal in question. We therefore write the adsorption energy as [4,8,10] ... 

Figure 4.6. Variations in the adsorption energy along the 4d transition metal series. The results of full DFT calculations are compared to those from the simple d band model and to experiments. Below the same data are plotted as a function of the d band center. Adapted from Ref. [4].

Figure 4.11. Calculated changes in the adsorption energy of atomic H and on a series of Pt(lll) surfaces, where the second layer has been replaced by a layer of 3d transition metals. To the right the variations in the d-projected density of states for the Pt surface atoms are shown. Adapted from Ref. [33].

Figure 4.42. The turnover frequencies for the low-temperature WGS reaction as a function of adsorption energies of oxygen and carbon monoxide. The positions of the step sites on noble and late transition metals are shown. As observed experimentally only copper appears to be a suitable pure metal catalyst for the process. Adapted from [139].

The effect of alkene structure on relative reactivity indicates that a much greater structural change in the alkenic moiety occurs on adsorption than in the change from adsorbed alkene to the transition state of the rate controlling surface reaction. Moreover, where measures indicate appreciable differences in adsorption energy, the more strongly adsorbed compound often exhibits the smaller zero order rate. 

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